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  Subjects -> METEOROLOGY (Total: 78 journals)
Acta Meteorologica Sinica     Hybrid Journal   (Followers: 2)
Advances in Atmospheric Sciences     Hybrid Journal   (Followers: 4)
Advances in Meteorology     Open Access   (Followers: 4)
Aeolian Research     Hybrid Journal   (Followers: 1)
Agricultural and Forest Meteorology     Hybrid Journal   (Followers: 6)
American Journal of Climate Change     Open Access   (Followers: 5)
Asian Journal of Earth Sciences     Open Access   (Followers: 17)
Atmósfera     Open Access  
Atmosphere     Open Access   (Followers: 2)
Atmosphere-Ocean     Full-text available via subscription   (Followers: 4)
Atmospheric Chemistry and Physics (ACP)     Open Access   (Followers: 11)
Atmospheric Chemistry and Physics Discussions (ACPD)     Open Access   (Followers: 7)
Atmospheric Research     Hybrid Journal   (Followers: 15)
Atmospheric Science Letters     Hybrid Journal   (Followers: 5)
Boundary-Layer Meteorology     Hybrid Journal   (Followers: 9)
Bulletin of the American Meteorological Society     Open Access   (Followers: 12)
Carbon Balance and Management     Open Access   (Followers: 5)
Climate     Open Access   (Followers: 1)
Climate Change Economics     Hybrid Journal   (Followers: 16)
Climate Dynamics     Hybrid Journal   (Followers: 13)
Climate law     Hybrid Journal   (Followers: 1)
Climate of the Past (CP)     Open Access   (Followers: 4)
Climate of the Past Discussions (CPD)     Open Access   (Followers: 2)
Climate Policy     Hybrid Journal   (Followers: 19)
Climate Risk Management     Open Access  
Climatic Change     Hybrid Journal   (Followers: 30)
Developments in Atmospheric Science     Full-text available via subscription   (Followers: 3)
Dynamics of Atmospheres and Oceans     Hybrid Journal   (Followers: 3)
Earth Perspectives - Transdisciplinarity Enabled     Open Access  
Energy & Environment     Full-text available via subscription   (Followers: 14)
Environmental and Climate Technologies     Open Access   (Followers: 1)
Global Meteorology     Open Access  
International Journal of Atmospheric Sciences     Open Access   (Followers: 2)
International Journal of Biometeorology     Hybrid Journal   (Followers: 1)
International Journal of Climate Change Strategies and Management     Hybrid Journal   (Followers: 6)
International Journal of Climatology     Hybrid Journal   (Followers: 12)
International Journal of Image and Data Fusion     Hybrid Journal  
ISRN Meteorology     Open Access  
Journal of Applied Meteorology and Climatology     Full-text available via subscription   (Followers: 7)
Journal of Atmospheric and Oceanic Technology     Full-text available via subscription   (Followers: 10)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 14)
Journal of Atmospheric Chemistry     Hybrid Journal   (Followers: 1)
Journal of Climate     Full-text available via subscription   (Followers: 22)
Journal of Climatology     Open Access  
Journal of Hydrology and Meteorology     Open Access   (Followers: 2)
Journal of Hydrometeorology     Full-text available via subscription   (Followers: 3)
Journal of Integrative Environmental Sciences     Hybrid Journal   (Followers: 3)
Journal of Meteorology and Climate Science     Full-text available via subscription  
Journal of Space Weather and Space Climate     Open Access   (Followers: 3)
Journal of the Atmospheric Sciences     Full-text available via subscription   (Followers: 21)
Journal of Weather Modification     Full-text available via subscription  
Large Marine Ecosystems     Full-text available via subscription   (Followers: 1)
Meteorologica     Open Access  
Meteorological Applications     Hybrid Journal   (Followers: 1)
Meteorologische Zeitschrift     Full-text available via subscription   (Followers: 2)
Meteorology and Atmospheric Physics     Hybrid Journal   (Followers: 2)
Michigan Journal of Sustainability     Open Access  
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 1)
Monthly Notices of the Royal Astronomical Society Letters     Hybrid Journal   (Followers: 1)
Monthly Weather Review     Full-text available via subscription   (Followers: 10)
Nature Climate Change     Full-text available via subscription   (Followers: 30)
Nature Reports Climate Change     Full-text available via subscription   (Followers: 14)
Open Journal of Modern Hydrology     Open Access   (Followers: 1)
Revista Brasileira de Meteorologia     Open Access   (Followers: 1)
Russian Meteorology and Hydrology     Hybrid Journal   (Followers: 3)
Space Weather     Full-text available via subscription   (Followers: 3)
Studia Geophysica et Geodaetica     Hybrid Journal   (Followers: 3)
Tellus A     Open Access   (Followers: 4)
Tellus B     Open Access   (Followers: 6)
The Cryosphere (TC)     Open Access   (Followers: 1)
The Cryosphere Discussions (TCD)     Open Access   (Followers: 1)
The Quarterly Journal of the Royal Meteorological Society     Hybrid Journal   (Followers: 5)
Theoretical and Applied Climatology     Hybrid Journal   (Followers: 2)
Weather     Hybrid Journal   (Followers: 2)
Weather and Climate Extremes     Open Access   (Followers: 2)
Weather and Forecasting     Full-text available via subscription   (Followers: 1)
Weatherwise     Hybrid Journal  
气候与环境研究     Full-text available via subscription  
Journal Cover Journal of Atmospheric and Solar-Terrestrial Physics
   [16 followers]  Follow    
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
     ISSN (Print) 1364-6826
     Published by Elsevier Homepage  [2563 journals]   [SJR: 0.955]   [H-I: 56]
  • Eastward electrojet enhancements during substorm activity
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): M. D'Onofrio , N. Partamies , E. Tanskanen
      In this study, we use a semi-automatic routine to identify negative and positive bays in the IMAGE magnetometer data during seven months in 2003. The IMAGE stations have been divided into three latitude regions to monitor the time evolution and temporal relationship between the regions during substorms. In particular, we focus on the events where both positive and negative ground magnetic deflections are observed in different latitude regions. We found 101 events in total. We examine separately a subset of 32 events, for which the local electrojet index values are larger than the global ones, suggesting that the strongest activity at that time takes place within or very close to the local time sector of IMAGE. We systematically analyze the temporal difference and the intensity of the positive and negative bays. Our results show that the magnitude of the positive bay is on average about half of that of the negative bay. Two thirds of the positive bays within the IMAGE network peak earlier than the negative bays. Because the positive and negative bays occur meridionally very close together, we suggest that the enhancements of the westward current at the poleward part of the auroral oval and the eastward current within the return flow are very tightly coupled through field-aligned currents and closing horizontal currents. The substorm current system appears as a superposition on the large-scale current pattern in the vicinity of the evening sector shear flow region.


      PubDate: 2014-08-16T01:22:45Z
       
  • Large-amplitude ULF waves at high latitudes
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): T. Guido , B. Tulegenov , A.V. Streltsov
      We present results from the statistical study of ULF waves detected by the fluxgate magnetometer in Gakona, Alaska during several experimental campaigns conducted at the High Frequency Active Auroral Research Program (HAARP) facility in years 2011–2013. We analyzed frequencies of ULF waves recorded during 26 strongly disturbed geomagnetic events (substorms) and compared them with frequencies of ULF waves detected during magnetically quiet times. Our analysis demonstrates that the frequency of the waves carrying most of the power in almost all these events is less than 1mHz. We also analyzed data from the ACE satellite, measuring parameters of the solar wind in the L1 Lagrangian point between Earth and Sun, and found that in several occasions there is a strong correlation between oscillations of the magnetic field in the solar wind and oscillations detected on the ground. We also found several cases when there is no correlation between signals detected on ACE and on the ground. This finding suggests that these frequencies correspond to the fundamental eigenfrequency of the coupled magnetosphere–ionosphere system, and the amplitude of these waves can reach significant magnitude when the system is driven by the external driver (for example, the solar wind) with this particular frequency. When the frequency of the driver does not match the frequency of the system, the waves still are observed, but their amplitudes are much smaller.


      PubDate: 2014-08-11T00:53:27Z
       
  • Optical observations of meteors generating infrasound—I: Acoustic
           signal identification and phenomenology
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): Elizabeth A. Silber , Peter G. Brown
      We analyse infrasound signals from 71 bright meteors/fireballs simultaneously detected by video to investigate the phenomenology and characteristics of meteor-generated near-field infrasound (<300km) and shock production. A taxonomy for meteor generated infrasound signal classification has been developed using the time–pressure signal of the infrasound arrivals. Based on the location along the meteor trail where the infrasound signal originates, we find most signals are associated with cylindrical shocks, with about a quarter of events evidencing spherical shocks associated with fragmentation episodes and optical flares. The video data indicate that all events with ray launch angles >117° from the trajectory heading are most likely generated by a spherical shock, while infrasound produced by the meteors with ray launch angles ≤117° can be attributed to both a cylindrical line source and a spherical shock. We find that meteors preferentially produce infrasound toward the end of their trails with a smaller number showing a preference for mid-trail production. Meteors producing multiple infrasound arrivals show a strong infrasound source height skewness to the end of trails and are much more likely to be associated with optical flares. We find that about 1% of all our optically-recorded meteors have associated detected infrasound and estimate that regional meteor infrasound events should occur on the order of once per week and dominate in numbers over infrasound associated with more energetic (but rarer) bolides. While a significant fraction of our meteors generating infrasound (~1/4 of single arrivals) are produced by fragmentation events, we find no instances where acoustic radiation is detectable more than about 60° beyond the ballistic regime at our meteoroid sizes (grams to tens of kilograms) emphasizing the strong anisotropy in acoustic radiation for meteors which are dominated by cylindrical line source geometry, even in the presence of fragmentation.


      PubDate: 2014-08-11T00:53:27Z
       
  • Artificial excitation of ELF waves with frequency of Schumann resonance
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): A.V. Streltsov , T. Guido , B. Tulegenov , J. Labenski , C.-L. Chang
      We report results from the experiment aimed at the artificial excitation of extremely low-frequency (ELF) electromagnetic waves with frequencies corresponding to the frequency of Schumann resonance. Electromagnetic waves with these frequencies can form a standing pattern inside the spherical cavity formed by the surface of the Earth and the ionosphere. In the experiment the ELF waves were excited by heating the ionosphere with X-mode HF electromagnetic waves generated at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska. The experiment demonstrates that heating of the ionosphere can excite relatively large-amplitude electromagnetic waves with frequencies in the range 7.8–8.0Hz when the ionosphere has a strong F layer, the frequency of the HF radiation is in the range 3.20–4.57MHz, and the electric field greater than 5mV/m is present in the ionosphere.


      PubDate: 2014-08-11T00:53:27Z
       
  • MAARSY multiple receiver phase calibration using radio sources
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Jorge L. Chau , Toralf Renkwitz , Gunter Stober , Ralph Latteck
      The Middle Atmosphere Alomar Radar System (MAARSY) on the Norwegian island of Andøya is a 53.5MHz monostatic radar with an active phased array antenna. The total array consists of 433 3-element linearly polarized Yagi antennas and can be configured to receive with multiple antenna sections (currently up to 16 complex receiving channels). In order to exploit its multiple-receiver capability for improving the space-time ambiguities of atmospheric/ionospheric targets, the phase difference between receiving channels has to be measured with good precision. Such phases are intrinsic to the system and are due to different cable lengths, pointing positions, filters, attenuators, amplifiers, antenna impedances, etc. In this work, we have operated MAARSY in a radio passive mode to observe the strong radio signals of Cassiopeia A and Cygnus A sources and calibrate the receiving system. By using the so-called fringe-stopping method, we have been able to calibrate the 16 complex channels, including the smaller antenna module that can be used, i.e., an Hexagon consisting of 7 Yagi antennas. The measured phases have been obtained with a mean standard deviation of ∼ 5 °. We have tested the validity of such phases using meteor-head echoes with different configurations and pointing directions. Given that the procedure is easy to implement, it should be used in a routine manner either to corroborate the stability of the system or to measure new phases after upgrades or repairs.


      PubDate: 2014-07-28T00:16:49Z
       
  • On the heterogeneous nucleation of mesospheric ice on meteoric smoke
           particles: Microphysical modeling
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): Heiner Asmus , Henrike Wilms , Boris Strelnikov , Markus Rapp
      Meteor smoke particles (MSP), which are thought to be the nucleation germs for mesospheric ice, are currently discussed to consist of highly absorbing materials such as magnesiowüstite, hematite or magnesium–iron-silicates and may therefore be warmer than the ambient atmosphere. In order to quantify the temperature difference between MSP and the atmosphere we developed a model to calculate the MSP equilibrium temperature in radiational and collisional balance. The temperature difference between MSP and the surrounding atmosphere strongly depends on the composition of the MSP, especially on the relative iron content, where a higher iron content leads to warmer MSP. We then derive an expression of the nucleation rate of mesospheric ice particles which explicitly accounts for this temperature difference. We find that the nucleation rate is strongly reduced by several orders of magnitude if the germ temperature is increased by only a few Kelvin. Implementing this nucleation rate depending on the germ temperature into CARMA, the Community Aerosol and Radiation Model for Atmospheres, we find that fewer but larger ice particles are formed compared to a reference scenario with no temperature difference between MSP and ambient atmosphere. This may indicate that iron-rich MSP are not ideal ice nuclei and that either other MSP-types or other nucleation pathways (e.g. wave induced heterogeneous nucleation or even homogeneous nucleation) are responsible for ice formation at the mesopause.


      PubDate: 2014-07-28T00:16:49Z
       
  • Windprofiler optimization using digital deconvolution procedures
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): W.K. Hocking , A. Hocking , D.G. Hocking , M. Garbanzo-Salas
      Digital improvements to data acquisition procedures used for windprofiler radars have the potential for improving the height coverage at optimum resolution, and permit improved height resolution. A few newer systems already use this capability. Real-time deconvolution procedures offer even further optimization, and this has not been effectively employed in recent years. In this paper we demonstrate the advantages of combining these features, with particular emphasis on the advantages of real-time deconvolution. Using several multi-core CPUs, we have been able to achieve speeds of up to 40GHz from a standard commercial motherboard, allowing data to be digitized and processed without the need for any type of hardware except for a transmitter (and associated drivers), a receiver and a digitizer. No Digital Signal Processor chips are needed, allowing great flexibility with analysis algorithms. By using deconvolution procedures, we have then been able to not only optimize height resolution, but also have been able to make advances in dealing with spectral contaminants like ground echoes and other near-zero-Hz spectral contamination. Our results also demonstrate the ability to produce fine-resolution measurements, revealing small-scale structures within the backscattered echoes that were previously not possible to see. Resolutions of 30m are possible for VHF radars. Furthermore, our deconvolution technique allows the removal of range-aliasing effects in real time, a major bonus in many instances. Results are shown using new radars in Canada and Costa Rica.


      PubDate: 2014-07-28T00:16:49Z
       
  • Detection of meteoric smoke particles in the mesosphere by a rocket-borne
           mass spectrometer
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): Scott Robertson , Shannon Dickson , Mihaly Horányi , Zoltan Sternovsky , Martin Friedrich , Diego Janches , Linda Megner , Bifford Williams
      In October 2011, two CHAMPS (Charge And Mass of meteoric smoke ParticleS) sounding rockets were launched into the polar mesosphere, each carrying an electrostatic multichannel mass analyzer for charged meteoric smoke particles (MSPs) that operated from 60 to 100km and returned data on the number density of the charged MSPs in several ranges of mass. The payloads also carried Faraday rotation antennas and an array of plasma probes for determining electron and ion densities and the payload charging potential, thus providing a comprehensive picture of the distribution of charges over a wide range of altitudes that can be compared with models for the vertical distribution of MSPs and for the distribution of charge. The launches were from the Andøya Rocket Range, Norway, following the end of the noctilucent cloud season to avoid detection of ice. A night launch (11 October 21:50 UT) and a day launch (13 October 13:50 UT) helped to elucidate the role of solar ultraviolet in determining the charge state of the particles. The night data show a distinct change in the charge state of MSPs at the D-region ledge (~78km) below which the density of free electrons is greatly reduced. Above the ledge, negative MSPs are detected at up to 92km, have number densities reaching ~200cm−3, and positive MSPs are absent. Below the ledge, positive and negative MSPs are about equally abundant, each with densities of ~2000cm−3 at 70km and with slightly lower densities at 60km. The MSPs are seen predominantly in mass bins spanning 500–2000amu and 2000–8000amu, with more massive particles (radii above ~1.2nm assuming a smoke particle density of 2g/cm3) having number densities below the detection threshold (10cm−3) and less massive particles being indistinguishable from ions. The daytime launch data show positive MSPs present only below the ledge and their number density is reduced to below 300cm−3. The daytime data show negative MSPs both above and below the D-region ledge and their number density is also reduced, perhaps as a consequence of photodetachment. Modeling of the charge state of the MSPs shows that the total number density of MSPs, charged and uncharged, is approximately 20,000cm−3 below the ledge and the model reproduces the absence of positive MSPs above the ledge.


      PubDate: 2014-07-28T00:16:49Z
       
  • Development of a digital receiver for range imaging atmospheric radar
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Masayuki K. Yamamoto , Toshiyuki Fujita , Noor Hafizah Binti Abdul Aziz , Tong Gan , Hiroyuki Hashiguchi , Tian-You Yu , Mamoru Yamamoto
      In this paper, we describe a new digital receiver developed for a 1.3-GHz range imaging atmospheric radar. The digital receiver comprises a general-purpose software-defined radio receiver referred to as the Universal Software Radio Peripheral 2 (USRP2) and a commercial personal computer (PC). The receiver is designed to collect received signals at an intermediate frequency (IF) of 130MHz with a sample rate of 10MSs−1. The USRP2 digitizes IF received signals, produces IQ time series, and then transfers the IQ time series to the PC through Gigabit Ethernet. The PC receives the IQ time series, performs range sampling, carries out filtering in the range direction, decodes the phase-modulated received signals, integrates the received signals in time, and finally saves the processed data to the hard disk drive (HDD). Because only sequential data transfer from the USRP2 to the PC is available, the range sampling is triggered by transmitted pulses leaked to the receiver. For range imaging, the digital receiver performs real-time signal processing for each of the time series collected at different frequencies. Further, the receiver is able to decode phase-modulated oversampled signals. Because the program code for real-time signal processing is written in a popular programming language (C++) and widely used libraries, the signal processing is easy to implement, reconfigure, and reuse. From radar experiments using a 1 - μ s subpulse width and 1-MHz frequency span (i.e., 2-MHz frequency bandwidth), we demonstrate that range imaging in combination with oversampling, which was implemented for the first time by the digital receiver, is able to resolve the fine-scale structure of turbulence with a vertical scale as small as 100m or finer.


      PubDate: 2014-07-28T00:16:49Z
       
  • A combined rocket-borne and ground-based study of the sodium layer and
           charged dust in the upper mesosphere
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): John M.C. Plane , Russell W. Saunders , Jonas Hedin , Jacek Stegman , Misha Khaplanov , Jörg Gumbel , Kristina A. Lynch , Phillip J. Bracikowski , Lynette J. Gelinas , Martin Friedrich , Sandra Blindheim , Michael Gausa , Bifford P. Williams
      The Hotel Payload 2 rocket was launched on January 31st 2008 at 20.14 LT from the Andøya Rocket Range in northern Norway (69.31° N, 16.01° E). Measurements in the 75–105km region of atomic O, negatively-charged dust, positive ions and electrons with a suite of instruments on the payload were complemented by lidar measurements of atomic Na and temperature from the nearby ALOMAR observatory. The payload passed within 2.58km of the lidar at an altitude of 90km. A series of coupled models is used to explore the observations, leading to two significant conclusions. First, the atomic Na layer and the vertical profiles of negatively-charged dust (assumed to be meteoric smoke particles), electrons and positive ions, can be modelled using a self-consistent meteoric input flux. Second, electronic structure calculations and Rice–Ramsperger–Kassel–Markus theory are used to show that even small Fe–Mg–silicates are able to attach electrons rapidly and form stable negatively-charged particles, compared with electron attachment to O2 and O3. This explains the substantial electron depletion between 80 and 90km, where the presence of atomic O at concentrations in excess of 1010 cm−3 prevents the formation of stable negative ions.


      PubDate: 2014-07-28T00:16:49Z
       
  • Long-term trends and decadal variability of upper mesosphere/lower
           thermosphere gravity waves at midlatitudes
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Christoph Jacobi
      Mesosphere/lower thermosphere (MLT) winds over Germany as measured with a low-frequency spaced receiver system at Collm 1984–2007 have been analysed with respect to variations at the time scales of gravity waves. Background winds are also registered to analyse possible gravity wave-mean flow interactions at decadal and interdecadal time scales. In both winter and summer an increasing mesospheric zonal wind jet with time is registered, which is accompanied with increasing gravity wave variances. At greater altitudes in summer, the mean wind jet trend reverses, and negative trends of gravity wave variances are found. This connection between gravity waves and mean wind is also observed on a quasi-decadal scale: during solar maximum stronger mesospheric zonal wind jets as well as larger gravity wave amplitudes are observed. This results in a solar cycle modulation of gravity waves with larger amplitudes during solar maximum. The observed positive correlation between gravity wave amplitudes and the mean zonal wind may follow the theory of saturated waves in the atmosphere, such that stronger mesospheric zonal winds are connected with larger gravity wave amplitudes.


      PubDate: 2014-07-28T00:16:49Z
       
  • Diurnal tides at low latitudes: Radar, satellite, and model results
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): G. Kishore Kumar , W. Singer , J. Oberheide , N. Grieger , P.P. Batista , D.M. Riggin , H. Schmidt , B.R. Clemesha
      Mean winds and tidal signatures in the mesosphere and lower thermosphere (MLT) region are derived from meteor radar observations at three sites around 22°S acquired in 2005. The observed differences of mean winds and tides are discussed in relation to the meteorological situation in the lower atmosphere and the possible generation of non-migrating tides. The longitudinally well separated radar sites allowed the evaluation of the migrating tidal component. The seasonal variation of signatures of the diurnal tide derived from ground-based radar observations, TIDI measurements aboard TIMED satellite, and model results obtained with HAMMONIA (Hamburg Model of the Neutral and Ionized Atmosphere) are compared. The ground-based, satellite, and model results of the total diurnal tide are in good agreement. The same is true for the migrating diurnal tide obtained from the radar observations, TIDI observations and from the model studies of HAMMONIA and GSWM00 (Global Scale Wave Model).


      PubDate: 2014-07-28T00:16:49Z
       
  • In-situ detection of noctilucent cloud particles by the Colorado Dust
           Detectors onboard the PHOCUS sounding rocket
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): Z. Sternovsky , S. Robertson , S. Dickson , J. Gumbel , J. Hedin , B. Strelnikov , H. Asmus , O. Havnes
      The Particles, Hydrogen and Oxygen Chemistry in the Upper Summer mesosphere (PHOCUS) sounding rocket campaign is a payload that carried multiple in-situ instruments for the detection of charged icy particles of noctilucent clouds (NLCs). The PHOCUS payload was launched on July 21st, 2011 and carried 18 scientific instruments. Three of these instruments were dedicated to the detection of the charged aerosol particles. All three instruments detected a narrow ice layer at around 81.5km altitude. The Colorado Dust Detectors (CDDs) collected the net charge from the impact of aerosol particles on two graphite surfaces mounted flush with the payload skin. A combination of a small bias potential and permanent magnets were used to suppress the collection of plasma particles. The efficiency of the magnetic shielding improves with increasing altitude where there are fewer scattering collisions with neutrals. The data analysis shows that the net collected current can be decomposed into contributions from photoelectron emission, plasma electrons and ions, and the aerosol particles. The results show that the current corresponding to the collection of aerosol particles is positive, which is due to secondary charging effects.


      PubDate: 2014-07-28T00:16:49Z
       
  • Bias correction and overall performance of a VHF Spaced Antenna boundary
           layer profiler for operational weather forecasting
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Bronwyn K. Dolman , Iain M. Reid
      Wind profiling radars are now in general use by a number of weather agencies worldwide. These use the Doppler Beam Swinging approach exclusively. The Australian Government Bureau of Meteorology has adopted a Boundary Layer wind profiling radar using the Spaced Antenna technique. This paper describes the performance of these radars and discusses some of the issues that needed to be addressed for appropriate performance in an operational environment, namely the known wind magnitude underestimation. The underestimation was successfully addressed with an empirical correction. Quality control and hardware improvements to minimize internal clutter have been implemented, resulting in largely outlier free wind estimates on presentation to forecasters, and excellent height coverage.


      PubDate: 2014-07-28T00:16:49Z
       
  • Program of the Antarctic Syowa MST/IS radar (PANSY)
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Kaoru Sato , Masaki Tsutsumi , Toru Sato , Takuji Nakamura , Akinori Saito , Yoshihiro Tomikawa , Koji Nishimura , Masashi Kohma , Hisao Yamagishi , Takashi Yamanouchi
      The PANSY radar is the first Mesosphere–Stratosphere–Troposphere/Incoherent Scatter (MST/IS) radar in the Antarctic region. It is a large VHF monostatic pulse Doppler radar operating at 47MHz, consisting of an active phased array of 1045 Yagi antennas and an equivalent number of transmit–receive (TR) modules with a total peak output power of 500kW. The first stage of the radar was installed at Syowa Station (69°00′S, 39°35′E) in early 2011, and is currently operating with 228 antennas and modules. This paper reports the project's scientific objectives, technical descriptions, and the preliminary results of observations made to date. The radar is designed to clarify the role of atmospheric gravity waves at high latitudes in the momentum budget of the global circulation in the troposphere, stratosphere and mesosphere, and to explore the dynamical aspects of unique polar phenomena such as polar mesospheric clouds (PMC) and polar stratospheric clouds (PSC). The katabatic winds as a branch of Antarctic tropospheric circulation and as an important source of gravity waves are also of special interest. Moreover, strong and sporadic energy inputs from the magnetosphere by energetic particles and field-aligned currents can be quantitatively assessed by the broad height coverage of the radar which extends from the lower troposphere to the upper ionosphere. From engineering points of view, the radar had to overcome restrictions related to the severe environments of Antarctic research, such as very strong winds, limited power availability, short construction periods, and limited manpower availability. We resolved these problems through the adoption of specially designed class-E amplifiers, light weight and tough antenna elements, and versatile antenna arrangements. Although the radar is currently operating with only about a quarter of its full designed system components, we have already obtained interesting results on the Antarctic troposphere, stratosphere and mesosphere, such as gravity waves, multiple tropopauses associated with a severe snow storm in the troposphere and stratosphere, and polar mesosphere summer echoes (PMSE).


      PubDate: 2014-07-28T00:16:49Z
       
  • Energetics of persistent turbulent layers underneath mid-level clouds
           estimated from concurrent radar and radiosonde data
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): R. Wilson , H. Luce , H. Hashiguchi , N. Nishi , Y. Yabuki
      Two Japanese-French field campaigns devoted to studying small-scale turbulence and instabilities in the lower atmosphere were conducted in September 2011 and November 2012 at the Shigaraki Middle and Upper atmosphere (MU) Observatory (34.85°N, 136.15°E; Japan). The Very High Frequency Middle and Upper atmosphere radar (MUR) was operated with a time resolution of the order of 10s in range imaging mode allowing echo power measurements at fine range-resolutions (typically, a few tens of meters). In addition, balloons instrumented with RS92G Vaisala radiosondes were launched from the observatory during the radar operations. From the raw data of temperature, pressure and humidity, temperature turbulent layers can be identified from the detection of overturns by using the Thorpe (1977) method. During the two campaigns, both radar and balloon data revealed turbulent layers of about 1.0km in depth, underneath mid-level clouds and meteorological frontal zones. They persisted for about 10h in the radar data. The balloon data collected were undoubtedly representative of the conditions met by the radar. Turbulence parameters associated with stably stratified flows were tentatively estimated by using different methods involving both radar and balloon observations for 4 balloon flights. These parameters included the Thorpe, buoyancy, and Ozmidov scales L T , L B and L O , potential and kinetic turbulent energies TPE and TKE, potential kinetic energy dissipation rates ε P and ε K and turbulent diffusivities K θ . The turbulence scales were found to be consistent between each other within a factor of about 2. Energy dissipation rates of 0.6mW/kg were found for 3 cases and 0.06mW/kg for one case.


      PubDate: 2014-07-28T00:16:49Z
       
  • IFC-Ed. board
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A




      PubDate: 2014-07-28T00:16:49Z
       
  • Preface to special issue: Mesospheric smoke and ice
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): Jorg Gumbel , Scott Robertson



      PubDate: 2014-07-28T00:16:49Z
       
  • The MAGIC meteoric smoke particle sampler
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): Jonas Hedin , Frank Giovane , Tomas Waldemarsson , Jörg Gumbel , Jürgen Blum , Rhonda M. Stroud , Layne Marlin , John Moser , David E. Siskind , Kjell Jansson , Russell W. Saunders , Michael E. Summers , Philipp Reissaus , Jacek Stegman , John M.C. Plane , Mihály Horányi
      Between a few tons to several hundred tons of meteoric material enters the Earth׳s atmosphere each day, and most of this material is ablated and vaporized in the 70–120km altitude region. The subsequent chemical conversion, re-condensation and coagulation of this evaporated material are thought to form nanometre sized meteoric smoke particles (MSPs). These smoke particles are then subject to further coagulation, sedimentation and global transport by the mesospheric circulation. MSPs have been proposed as a key player in the formation and evolution of ice particle layers around the mesopause region, i.e. noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). MSPs have also been implicated in mesospheric heterogeneous chemistry to influence the mesospheric odd oxygen/odd hydrogen (O x /HO x ) chemistry, to play an important role in the mesospheric charge balance, and to be a significant component of stratospheric aerosol and enhance the depletion of O3. Despite their apparent importance, little is known about the properties of MSPs and none of the hypotheses can be verified without direct evidence of the existence, altitude and size distribution, shape and elemental composition. The aim of the MAGIC project (Mesospheric Aerosol – Genesis, Interaction and Composition) was to develop an instrument and analysis techniques to sample for the first time MSPs in the mesosphere and return them to the ground for detailed analysis in the laboratory. MAGIC meteoric smoke particle samplers have been flown on several sounding rocket payloads between 2005 and 2011. Several of these flights concerned non-summer mesosphere conditions when pure MSP populations can be expected. Other flights concerned high latitude summer conditions when MSPs are expected to be contained in ice particles in the upper mesosphere. In this paper we present the MAGIC project and describe the MAGIC MSP sampler, the measurement procedure and laboratory analysis. We also present the attempts to retrieve MSPs from these flights, the challenges inherent to the sampling of nanometre sized particles and the subsequent analysis of the sampled material, and thoughts for the future. Despite substantial experimental efforts, the MAGIC project has so far failed to provide conclusive results. While particles with elemental composition similar to what is to be expected from MSPs have been found, the analysis has been compromised by challenges with different types of contamination and uncertainties in the sticking efficiency of the particles on the sampling surfaces.


      PubDate: 2014-07-28T00:16:49Z
       
  • Emissions of ionospheric Alfvén resonator and ionospheric conditions
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): A.S. Potapov , T.N. Polyushkina , B.V. Dovbnya , B. Tsegmed , R.A. Rakhmatulin
      We analyze continuous magnetic observations of ionospheric Alfvén resonator (IAR) emissions at mid-latitude observatory Mondy. The measurements were by a LEMI-30 search-coil magnetometer covering the period from March 2010 to May 2011. The results are compared with data from simultaneous ionospheric sounding data and International Reference Ionosphere (IRI-2012) model parameters. The large amount of observational data allowed us to inspect the daily and seasonal variations in some morphological characteristics of the emissions as well as their relationship to ionospheric conditions. The main factor affecting the duration of the emission is how long the lower ionosphere stays in Earth's shadow. We demonstrate a close inverse correlation between the diurnal and seasonal IAR frequency variations, on the one hand, and changes in the ionospheric critical frequency, f 0F2, on the other. Additionally, the expected emission frequency scale calculated with the IRI-2012 model is in good agreement with the values measured from the emission spectrograms.


      PubDate: 2014-07-28T00:16:49Z
       
  • IFC-Ed. board
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B




      PubDate: 2014-07-28T00:16:49Z
       
  • Stratospheric and mesospheric concentric gravity waves over tropical
           cyclone Mahasen: Joint AIRS and VIIRS satellite observations
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): Jia Yue , Steven D. Miller , Lars Hoffmann , William C. Straka III
      We report on the first simultaneous spaceborne observations of concentric gravity wave patterns in the stratosphere and mesosphere over the Indian Ocean excited by Tropical Cyclone Mahasen. On the nights of 13–14 May 2013, concentric ring patterns in nightglow were observed in close-proximity to Mahasen by the Day/Night Band (DNB) of the Visible/Infrared Imager/Radiometer Suite (VIIRS) on the Suomi NPP satellite. The waves exhibited horizontal wavelengths of 40–60km. On 13 May 2013, long concentric waves of ~500km wavelength were also seen west of India, far away (~1500km) from their estimated center near Mahasen. Concentric gravity waves in the stratosphere were observed nearly simultaneously by the Atmospheric Infrared Sounder on the Aqua satellite. These multi-level observations provide a clearer picture of the complex three-dimensional structure of tropical cyclone-generated gravity waves than a single instrument alone.


      PubDate: 2014-07-28T00:16:49Z
       
  • Traveling planetary wave activity from mesopause region airglow
           temperatures determined by the Network for the Detection of Mesospheric
           Change (NDMC)
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): E.R. Reisin , J. Scheer , M.E. Dyrland , F. Sigernes , C.S. Deehr , C. Schmidt , K. Höppner , M. Bittner , P.P. Ammosov , G.A. Gavrilyeva , J. Stegman , V.I. Perminov , A.I. Semenov , P. Knieling , R. Koppmann , K. Shiokawa , R.P. Lowe , M.J. López-González , E. Rodríguez , Y. Zhao , M.J. Taylor , R.A. Buriti , P.J. Espy , W.J.R. French , K.-U. Eichmann , J.P. Burrows , C. von Savigny
      The global distribution of traveling planetary wave (PW) activity in the mesopause region is estimated for the first time from ground-based airglow measurements. Monthly and total mean climatologies of PW power are determined from rotational temperatures measured at 19 sites from 78° N to 76° S which contribute to the Network for the Detection of Mesospheric Change (NDMC). Wave power is expressed as the standard deviation of nocturnal mean temperature around the seasonal temperature variation. The results from 20° N confirm the SABER traveling PW proxy by Offermann et al. (2009, J. Geophys. Res. 114, D06110) at two altitudes. Most sites between 69° S and 69° N show total mean traveling PW activity of about 6K, and only some high latitude sites have considerably higher activity levels. At the two tropical sites, there is practically no seasonal variation of PW activity. At 70% of the midlatitude sites, the seasonal variation is moderate for most of the year, but it is quite appreciable at all high latitude sites. Results about traveling PW activity at 87km and 95km available from several sites signal similar behavior at both altitudes. The total mean climatological results here obtained have further been used to separate the traveling PW contribution from the superposition of wave types contained in OH rotational temperature fluctuations measured by the SCIAMACHY instrument on Envisat. A narrow equatorial wave activity maximum is probably caused by gravity waves, while a tendency towards greater activity at higher northern latitudes may be due to stationary planetary waves.


      PubDate: 2014-07-28T00:16:49Z
       
  • Comparisons between multiple in-situ aircraft turbulence measurements and
           radar in the troposphere
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Armin Dehghan , Wayne K. Hocking , Ramesh Srinivasan
      Networks of Windprofiler Radars have the capability to make significant contributions to severe weather forecasting (both on the ground and in the air) through the determination of real-time turbulence strengths, but the potential has still not been fully realized. In order to better understand the accuracy of profilers in determination of turbulence strengths, we have compared radar measurements made at the Harrow radar in Canada (located in Southwestern Ontario as part of the O-QNet radar network) with in-situ measurements made by multiple aircraft. These included measurements made both by commercial aircraft and dedicated research aircraft. Research aircraft (instrumented with accelerometers and GPS tracking devices) and radar data were analysed using structure function, spectral and spectral-width methods. Data were also recorded on-board commercial aircraft using accelerometer-based studies, and results were recorded for subsequent analyses. Over 92,000 commercial aircraft measurements, 4000h of radar data, and 15 days of research-aircraft measurements were available for this study, although only a subset of the commercial aircraft data were useable. The radar-based spectral-width method occasionally produced anomalous negative values of the turbulence strength, usually associated with weak turbulence coupled with significant wind variability over scales of tens of kms, but the aircraft data also had limitations. For the commercial aircraft, frequent zeros were common, also associated with weak turbulence. With regard to the research aircraft measurements, it was found through both spectral and structure function analyses that spectral contaminants exist out to scales of many tens of metres (larger than often assumed), but proper allowance for these effects permitted good estimates of turbulence strength. Spatial and temporal variability was large, however, complicating comparisons with the radar. By comparing the in-situ data to the radar data, it has been possible to place stronger limits on the constants used to determine radar turbulence strengths. Subsequent comparisons with the commercial aircraft data over a six-month period have then been used to show that aircraft and radar probability distributions agree in form, but that the aircraft data are three to five times larger. Corrections for this bias lead to good agreement, both in form and absolute values, for all three data sets.


      PubDate: 2014-07-28T00:16:49Z
       
  • Multi-radar observations of polar mesosphere summer echoes during the
           PHOCUS campaign on 20–22 July 2011
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): E. Belova , S. Kirkwood , R. Latteck , M. Zecha , H. Pinedo , J. Hedin , J. Gumbel
      During the PHOCUS rocket campaign, on 20–22 July 2011, the observations of polar mesosphere summer echoes (PMSE) were made by three mesosphere–stratosphere–troposphere radars, operating at about 50MHz. One radar, ESRAD is located at Esrange in Sweden, where the rocket was launched, two other radars, MAARSY and MORRO, are located 250km north-west and 200km north of the ESRAD, respectively, on the other side of the Scandinavian mountain ridge. We compared PMSE as measured by these three radars in terms of their strength, spectral width and wave modulation. Time–altitude maps of PMSE strength look very similar for all three radars. Cross-correlations with maximum values 0.5–0.6 were found between the signal powers over the three days of observations for each pair of radars. By using cross-spectrum analysis of PMSE signals, we show that some waves with periods of a few hours were observed by all three radars. Unlike the strengths, simultaneous values of PMSE spectral width, which is related to turbulence, sometimes differ significantly between the radars. For interpretation of the results we suggested that large-scale fields of neutral temperature, ice particles and electron density, which are more or less uniform over 150–250km horizontal extent were ‘modulated’ by waves and smaller patches of turbulence.


      PubDate: 2014-07-28T00:16:49Z
       
  • On the size distribution of collision fragments of NLC dust particles and
           their relevance to meteoric smoke particles
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part B
      Author(s): O. Havnes , J. Gumbel , T. Antonsen , J. Hedin , C. La Hoz
      We present the results from a new dust probe MUDD on the PHOCUS payload which was launched in July 2011. In the interior of MUDD all the incoming NLC/PMSE icy dust particles will collide, at an impact angle ~70° to the surface normal, with a grid constructed such that no dust particles can directly hit the bottom plate of the probe. Only collision fragments will continue down towards the bottom plate. We determine an energy distribution of the charged fragments by applying a variable electric field between the impact grid and the bottom plate of MUDD. We find that ~30% of the charged fragments have kinetic energies less than 10eV, ~20% have energies between 10 and 20eV while ~50% have energies above 20eV. The transformation of limits in kinetic energy for ice or meteoric smoke particles (MSP) to radius is dependent on many assumptions, the most crucial being fragment velocity. We find, however, that the sizes of the charged fragments most probably are in the range of 1 to 2nm if meteoric smoke particles (MSP), and slightly higher if ice particles. The observed high charging fraction and the dominance of fragment sizes below a few nm makes it very unlikely that the fragments can consist mainly of ice but that they must be predominantly MSP as predicted by Havnes and Næsheim (2007) and recently observed by Hervig et al. (2012). The MUDD results indicate that MSP are embedded in NLC/PMSE ice particles with a minimum volume filling factor of ~.05% in the unlikely case that all embedded MSP are released and charged. A few % volume filling factor (Hervig et al., 2012) can easily be reached if ~10% of the MSP are released and that their charging probability is ~0.1.


      PubDate: 2014-07-28T00:16:49Z
       
  • Westward traveling planetary wave events in the lower thermosphere during
           solar minimum conditions simulated by SD-WACCM-X
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): Fabrizio Sassi , Han-Li Liu
      We present numerical simulations with the Whole Atmosphere Community Climate Model, eXtended version (WACCM-X), whose dynamics is constrained by atmospheric specifications during recent and historical solar minimum conditions. The focus of this study is to describe how various dynamical conditions of boreal winter affect the dynamical behavior of the lower thermosphere (90–150km). The model simulations are carried out during solar minimum conditions and the results shown here discuss the period January 1–March 30 for five years (1995, 1996, 2008, 2009, and 2010). These years were selected because they include boreal winters without stratospheric warming (1995 and 1996), with modest or normal stratospheric warming (2008 and 2010), and with a large and persistent stratospheric warming (2009). The ultimate goal of this study is to encapsulate the statistically significant dynamical behavior due to westward propagating, planetary-scale waves (wavenumber 1 and wavenumber 2) in the lower thermosphere that are associated with different stratospheric conditions. To this end we show that the westward zonal acceleration above about 80km is by and large described by traveling waves with periods between 2 and 10 days. We show that the momentum carried by these waves is unlikely to affect directly the momentum budget of the extra-tropical lower thermosphere, where instead gravity-wave drag figures prominently. However, at the times leading to and following large stratospheric disturbances, we show prominent meridional propagation of wave activity from the mid-latitudes toward the tropics. In combination with strong eastward meridional wind shear, our results provide further evidence that such equatorward propagation of momentum in the lower thermosphere might influence the amplitude of equatorially trapped tides.


      PubDate: 2014-07-28T00:16:49Z
       
  • Comparative studies on ionospheric climatological features of NmF2 among
           the Arctic and Antarctic stations
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): Sheng Xu , Bei-Chen Zhang , Rui-Yuan Liu , Li-Xin Guo , Ye-Wen Wu
      Climatological features of the maximum electron density of the ionospheric F2 region (NmF2) are investigated and compared among the Arctic and Antarctic stations using long-term observations from the dynasonde measurements at Tromso, the EISCAT Svalbard Radar (ESR) measurements at Longyearbyen, and the digisonde DPS-4 measurements at Zhongshan, Antarctica. The NmF2 data are sorted as monthly medians of NmF2 for each hour, month, and solar activity. Results are presented as follows: (1) On the diurnal variability, the maximum value of NmF2 mainly occurs at local noon at the auroral latitude station Tromso, but at magnetic noon at the cusp latitude station Longyearbyen and between local noon and magnetic noon at Zhongshan, indicating the importance of soft particle precipitation and ionospheric convection in the cusp region. (2) In addition to the daytime peak, there is another peak just before magnetic midnight at Longyearbyen in winter during solar maximum years, which is attributed to the cross-polar transport of EUV ionization from day side to night side. (3) An enhancement of NmF2 is detected at magnetic midnight in winter at Tromso. It may be caused by the nighttime substorms. (4) On the seasonal variability, there are semi-annual anomaly at Tromso and normal variability at both Longyearbyen and Zhongshan during solar minimum years. (5) During solar maximum years there is always semi-annual anomaly for all three stations. The well-known winter anomaly is evident at both Tromso and Zhongshan, but does not exist at Longyearbyen. These anomalies are mainly due to the differences in photoionization and chemical compositions between the three stations.


      PubDate: 2014-07-28T00:16:49Z
       
  • First results on forecasting the spatial occurrence pattern of L-band
           scintillation and its temporal evolution
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): R. Sridharan , Mala S. Bagiya , Surendra Sunda , Rajkumar Choudhary , Tarun K. Pant , Lijo Jose
      After a fairly successful attempt to forecast the temporal evolution of L-band scintillation over a given location, Trivandrum (8.5° N, 76.91° E, dip latitude 0.5° N) (Sridharan et al., 2012, J. Atmos. Sol. Terr. Phys. 80 230–238; Bagiya et al., 2014, J. Atmos. Sol. Terr. Phys. 110–111, 15–22), an attempt has been made here to generate the spatial–temporal maps of the occurrence pattern of L-band scintillation over the Indian region. To start with, the day time fluctuations in [f0F2]2 are used to forecast the temporal evolution of perturbations during the course of the night over Trivandrum. Similar to the earlier studies, here too it is taken that the electron density perturbations retain their characteristics throughout night and traverse with a uniform velocity. This implies that when the integrity of wave train of electron density perturbations is retained, any particular feature that passes over Trivandrum would have crossed over another location west of Trivandrum at an earlier time only dictated by the zonal velocity. With this assumption it becomes feasible to generate the probable spatial and temporal pattern of L-band scintillation. The consequences/limitations of the above assumptions are discussed in detail. The observed relation between the total duration of spread-F and the base height of the F-region (h'F) at 1930LT has been explained in terms of the favourable background neutral atmospheric conditions. Following Bagiya et al. (2013, J. Geophys. Res. 118, 1–8), the relation between h'F at 1930LT and the probable maximum latitudinal extent of the spread-F enables specification of the upper limit for the latitudes likely to be affected by the scintillation. It is believed that the presented results hold enough potential to generate the reliable L-band scintillation forecast maps and provide the necessary alerts to the satellite based air navigation users.


      PubDate: 2014-07-28T00:16:49Z
       
  • The scattering simulation of DSDs and the polarimetric radar rainfall
           algorithms at C-band frequency
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): Tanvir Islam
      This study explores polarimetric radar rainfall algorithms at C-band frequency using a total of 162,415 1-min raindrop spectra from an extensive disdrometer dataset. Five different raindrop shape models have been tested to simulate polarimetric radar variables—the reflectivity factor (Z), differential reflectivity (Z dr ) and specific differential phase (K dp ), through the T-matrix microwave scattering approach. The polarimetric radar rainfall algorithms are developed in the form of R(Z), R(K dp ), R(Z, Z dr ) and R(Z dr , K dp ) combinations. Based on the best fitted raindrop spectra models rain rate retrieval information using disdrometer derived rain rate as a reference, the algorithms are further explored in view of stratiform and convective rain regimes. Finally, an “artificial” algorithm is proposed which considers the developed algorithms for stratiform and convective regimes and uses R(Z), R(K dp ) and R(Z, Z dr ) in different scenarios. The artificial algorithm is applied to and evaluated by the Thurnham C-band dual polarized radar data in 6 storm cases perceiving the rationalization in terms of rainfall retrieval accuracy as compared to the operational Marshall–Palmer algorithm (Z=200R 1.6). A dense network of 73 tipping bucket rain gauges is employed for the evaluation, and the result demonstrates that the artificial algorithm outperforms the Marshall–Palmer algorithm showing R 2=0.84 and MAE=0.82mm as opposed to R 2=0.79 and MAE=0.86mm respectively.


      PubDate: 2014-07-28T00:16:49Z
       
  • Plasma bubbles in the topside ionosphere: Estimations of the survival
           possibility
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): L.N. Sidorova , S.V. Filippov
      The question about the survival possibility and the life duration of the topside ionosphere equatorial spread F (ESF) plasma bubbles observed in the separate ion component (He+) is investigated. For this aim the main aeronomy processes, in which plasma bubbles and their He+ ions are involved, were under consideration. It was obtained that the main competition takes place between the He+ loss reactions (He+–N2 reaction) and the uplift during linear growth phase (~10min) of the Rayleigh–Taylor (R–T) instability, when the plasma bubbles are forming. It was revealed that the ambipolar diffusion of the He+ ions inside the plasma bubble is the fastest (~1–2min) in the altitude region up to 500km and becomes slower (~1h) above 500km. On the other hand, the plasma bubbles seen in He+ density are pretty stable structures against the cross-field (Bohm) diffusive collapse. It was concluded that the ESF plasma bubbles, reaching the “ceiling” heights, can exist for a night and several morning hours (~10–13h) and that there is a principal opportunity to observe them in the separate ion component (He+).


      PubDate: 2014-07-28T00:16:49Z
       
  • Effects of melting layer on Ku-band signal depolarization
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): Thumree Sarkar , Saurabh Das , Animesh Maitra
      Propagation effects on Ku-band over an earth-space path is carried out at Kolkata, India, a tropical location, by receiving a Ku-band signal with horizontal plane polarization transmitted from the geostationary satellite NSS-6 (at 95°E). The amplitude of co-polar attenuation has been monitored along with the measurements of rain rate, rain drop size distribution and height profile of rain rate. The cross-polar enhancement of the signal is also monitored by receiving the same signal in orthogonal direction with another identical receiver. The experimental observations are used to study the effect of melting layer on both co-polar attenuation and cross-polar enhancement for the rain events observed during 2012–2013. Melting layer is indicated by the bright band signature in vertical profile of rain rate. The ground based drop size measurements indicate that the stratiform rain has more number of small drops whereas convective rain composed of large rain drops. The results indicate that the depolarization due to melting layer is more dominant compared to that due to the drop deformation mechanism at low rain rates.


      PubDate: 2014-07-28T00:16:49Z
       
  • IFC-Ed. board
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117




      PubDate: 2014-07-28T00:16:49Z
       
  • Loss of synchronization in the 27-day spectral component of geomagnetic
           indices and its relationship with solar activity
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): Elena Blanter , Jean-Louis Le Mouël , Mikhail Shnirman , Vincent Courtillot
      We investigate the “27-day” spectral component of different global (aa and Dst) and local ( ζ ) geomagnetic indices in two period ranges relevant to the Sun׳s synodic rotation, as manifested by magnetic activity: 24–28 days (short) and 28–32 days (long). Cross-correlation analysis of the respective energies of the short and long periods of the 27-day rotation signal in the same geomagnetic index reveals well-defined de-synchronization events during certain solar cycles. The largest de-synchronization in the past century occurred during solar cycle 21. De-synchronization events first occur in indices of the Dst (and ζ ) family, and then in indices of the aa family. We found no evidence that the strength of the de-synchronization of the solar rotation signal in the ζ -index would depend on geomagnetic latitude. Applying the same analysis to proper solar indices (sunspot number, F10.7 radio flux, interplanetary magnetic field (IMF) series, solar wind speed), we find that only the Bz component of the IMF demonstrates a de-synchronization, during solar cycle 21, between the energies of the 27-day solar rotation signal in the short and long period ranges. We discuss possible implications of these results with respect to the evolution of the toroidal and poloidal components of the Sun׳s magnetic field and to its large-scale structures.


      PubDate: 2014-07-28T00:16:49Z
       
  • The diffusion of multiple ionic species in meteor trails
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): J.P. Younger , I.M. Reid , R.A. Vincent
      Meteor trails are composed of a number of different types of ions that are produced during the meteoroid ablation process. The diffusion of meteoric plasma is usually presented in terms of the diffusion of a single ionic species, but this ignores the possibility of non-linear diffusion due to complex meteor trail composition. This study uses numerical simulations to investigate what effect multi-ion diffusion has on the time-decay of meteor radar echoes, and whether multi-ion diffusion could be responsible for the anomalous diffusion coefficient estimates produced by radars operating at different frequencies. It is found that the diffusion of different species of ions in meteor trails does not produce the same discrepancies seen in estimates of the ambipolar diffusion coefficient made using meteor radar.


      PubDate: 2014-07-28T00:16:49Z
       
  • Electron–ion temperature ratio estimations in the summer polar
           mesosphere when subject to HF radio wave heating
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): H. Pinedo , C. La Hoz , O. Havnes , M. Rietveld
      We have inferred the electron temperature enhancements above mesospheric altitudes under Polar Mesospheric Summer Echoes (PMSE) conditions when the ionosphere is exposed to artificial HF radio wave heating. The proposed method uses the dependence of the radar cross section on the electron-to-ion temperature ratio to infer the heating factor from incoherent scatter radar (ISR) power measurements above 90km. Model heating temperatures match our ISR estimations between 90 and 130km with 0.94 Pearson correlation index. The PMSE strength measured by the MORRO MST radar is about 50% weaker during the heater-on period when the modeled electron-to-ion mesospheric temperature is approximately 10 times greater than the unperturbed value. No PMSE weakening is found when the mesospheric temperature enhancement is by a factor of three or less. The PMSE weakening and its absence are consistent with the modeled mesospheric electron temperatures. This consistency supports to the proposed method for estimating mesospheric electron temperatures achieved by independent MST and ISR radar measurements.


      PubDate: 2014-07-28T00:16:49Z
       
  • PMSE strength during enhanced D region electron densities: Faraday
           rotation and absorption effects at VHF frequencies
    • Abstract: Publication date: October 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 118, Part A
      Author(s): Jorge L. Chau , Jürgen Röttger , Markus Rapp
      In this paper we study the effects of absorption and Faraday rotation on measurements of polar mesosphere summer echoes (PMSE). We found that such effects can produce significant reduction of signal-to-noise ratio (SNR) when the D region electron densities (N e ) are enhanced, and VHF radar systems with linearly polarized antennas are used. In particular we study the expected effects during the strong solar proton event (SPE) of July 2000, also known as the Bastille day flare event. During this event, a strong anti-correlation between the PMSE SNR and the D-region N e was found over three VHF radar sites at high latitudes: Andøya, Kiruna, and Svalbard. This anti-correlation has been explained (a) in terms of transport effects due to strong electric fields associated to the SPE and (b) due to a limited amount of aerosol particles as compared to the amount of D-region electrons. Our calculations using the N e profiles used by previous researchers explain most, if not all, of the observed SNR reduction in both time (around the SPE peak) and altitude. This systematic effect, particularly the Faraday rotation, should be recognized and tested, and possibly avoided (e.g., using circular polarization), in future observations during the incoming solar maximum period, to contribute to the understanding of PMSE during enhanced D region N e .


      PubDate: 2014-07-28T00:16:49Z
       
  • Comparison of H+ and He+ plasmapause locations based on the resurrected
           and reevaluated OGO-5 ion composition data base
    • Abstract: Publication date: November 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
      Author(s): Vladimír Truhlík , Ludmila Třísková , Robert F. Benson , Dieter Bilitza , Joseph Grebowsky , Phil G. Richards
      Orbiting Geophysical Observatory 5 (OGO 5) magnetospheric ion-composition data (H+, He+ and O+) have been retrieved from old magnetic tapes archived at the National Space Science Data Center (NSSDC). The highly compressed binary format was converted into a user-friendly ASCII format and these data have been made available online. We have inspected the reliability and consistency of this data set. Comparisons with the IRI-2012 climatological model and the FLIP theoretical model revealed a shift of absolute and relative ion densities with time. Here we have developed a correction procedure for the individual H+, He+ and O+ ion density measurements. We investigated plasmapause locations based on the density gradients in H+, and He+. The correlation coefficient between these locations was determined to be ~0.886 with the typical difference in L about 0.1. The electron density at the He+ plasmapause location based on the corrected data for all cases was >100cm−3.


      PubDate: 2014-07-28T00:16:49Z
       
  • Intercomparison of various SA Techniques on wind estimation using multi
           receiver phased array radar
    • Abstract: Publication date: Available online 16 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Shridhar Kumar , V.K. Anandan , V.N. Sureshbabu , T. Narayana Rao , M. Purnachandra Rao , Toshitaka Tsuda
      In this paper we have applied various spaced antenna (SA) techniques to derive horizontal winds with Middle and Upper (MU) atmospheric radar observations. SA techniques comprise different analysis method like Full Correlation Analysis (FCA), Cross Correlation Ratio (CCR), Slope at Zero lag (SZL) and Intersection (INT) methods etc. Among these methods, FCA is considered one of the classical approaches. In the present study, the MU radar antenna array is regrouped (in software) into three different antenna segments, each segment consists of 8 channels and forming an equilateral triangle. Grouping of antenna has been done with 4 different orientations by interchanging the channels. FCA wind has been estimated with an equilateral triangle grouping of antenna array in all orientations. With the same grouping in different orientation, winds are estimated with CCR, SZL and INT method. Winds estimated with different orientation are averaged to obtain the mean winds component. In most of studies reported earlier using CCR, SZL and INT method, winds have been estimated with pair of antenna having baseline parallel to the antenna array plane. We have retrieved the zonal wind with a pair of antennas having baseline parallel to the antenna array plane in East-west direction and meridional wind is estimated with a pair of antennas having baseline parallel to the antenna array plane in North-south direction.The mean winds obtained with various SA techniques are compared with that observed by the Doppler Beam swinging (DBS) technique and GPS-sonde. It is observed that mean winds obtained with the approach adopted using different spatially distributed array grouping has yielded higher height coverage up to ∼20km and in good agreement with the results obtained using DBS observations even with a temporal resolution of ∼1.3min in clear air condition. Various statistical analyses like correlation analysis, standard deviation, Root mean square error (RMSE) and error analysis have been performed to understand the performance of other techniques in comparison with FCA. The analysis is carried out for an observation of 6hours for two different observation periods.


      PubDate: 2014-06-14T18:17:08Z
       
  • Prefa Recent progress from networked studies based around MST radar
    • Abstract: Publication date: Available online 29 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Wayne K. Hocking , Volker Lehmann , Werner Singer , Masayuki Yamamoto



      PubDate: 2014-06-14T18:17:08Z
       
  • Hybrid model for long-term prediction of the ionospheric global TEC
    • Abstract: Publication date: Available online 24 May 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): P. Mukhtarov , D. Pancheva , B. Andonov
      A new hybrid climatological model for long-term prediction of the global TEC was developed. It is based on the global empirical background TEC model constructed by Mukhtarov et al. (2013a,b) and the availability of regularly/new observations from CODE TEC data. The cornerstone of the hybrid model consists of applying the method of autocorrelation prediction of the error and the respective correction of the background model with the predicted error. An important question is how the efficiency of the correction procedure depends on the given offset, i.e. the time distance between the dates for which the prediction is made to that with real data. It was found that the correction is really effective if the error prediction is made for a date with a distance up to 60 days from the date with real data. Then the RMSE decreases from 3.2 TECU (for the global background TEC model) to 2.76 TECU (for the hybrid model) which demonstrates the advantage of the presented in this paper hybrid model for long-term prediction with respect to the originally built background TEC model.


      PubDate: 2014-06-14T18:17:08Z
       
  • Electric field signatures of the IAR and Schumann resonance in the upper
           ionosphere detected by Chibis-M microsatellite
    • Abstract: Publication date: Available online 3 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): D. Dudkin , V. Pilipenko , V. Korepanov , S. Klimov , R. Holzworth
      We tried to find with the ULF/ELF electric field sensor onboard Chibis-M microsatellite signatures of the IAR (Ionospheric Alfvén Resonator) and Schumann Resonance (SR) in the upper ionosphere. Whereas observations of the IAR and SR multi-band emissions with ground magnetometers are ubiquitous, in-situ satellite observations of their signatures are very rare. ULF events detected by the Chibis-M show a possibility of triggered excitation of IAR. In contrast to dominating view, IAR has been found to be effectively excited on the dayside, too. Chibis-M observations also supported the possibility of the SR leakage into the upper ionosphere.


      PubDate: 2014-06-14T18:17:08Z
       
  • Comparison of GPS-TEC measurements with IRI-2007 and IRI-2012 modeled TEC
           at an equatorial latitude station, Bangkok, Thailand
    • Abstract: Publication date: Available online 9 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Sanit Arunpold , Nitin K. Tripathi , V. Rajesh Chowdhary , Durairaju Kumaran Raju
      This paper presents the first vertical total electron content (VTEC) data derived from a dual-frequency GPS receiver installed at the Asian Institute of Technology in Bangkok, as part of project SCINDA (Scintillation Network and Decision Aid). with a magnetic dip latitude of 14°N, The diurnal, monthly, and seasonal variation in TEC, measured between August 2010 and July 2012, was compared with values derived from two International Reference Ionosphere (IRI) models: the IRI-2007 and the recently released IRI-2012. The highest diurnal TEC always occurred between 08:00 and 12:00 Universal Time (UT). The diurnal pattern of GPS-TEC reached its maximum values during equinoctial months (March, April, September, and October) and minimum values during solstice months (June, July, December, and January), which can be attributed to the solar extreme ultra-violet ionization coupled with the upward vertical ExB drift. The modeled TEC was underestimated in 2010 and 2011 and overestimated in 2012, especially with the IRI-2007 model. The measured values were better correlated with the IRI-2012 model, especially in 2012. However, neither of the IRI models responded to geomagnetic activity, despite the selection of the “storm” option, generally showing a smooth curve and underestimating TEC during a storm. To verify this phenomenon, the impacts of geomagnetic storms were considered.


      PubDate: 2014-06-14T18:17:08Z
       
  • Equinoctial asymmetry in low latitude ionosphere as observed by SROSS-C2
           satellite
    • Abstract: Publication date: Available online 11 June 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics
      Author(s): Ananna Bardhan , Malini Aggarwal , D.K. Sharma , J. Rai
      The ionospheric plasma parameters (electron, ion temperatures and ion composition-Te, Ti, O+ and H+) measured by SROSS-C2 satellite at an average altitude of ~500km has been investigated to study the behaviour of the ionosphere in equinoxes during half a solar cycle (year 1995 to 2000, F10.7~70 to 195). The region under study spans over 5°–35°N geog. latitude and 65°–95°E geog. longitude in the Indian sector. We found an equinoctial asymmetry in the diurnal behaviour of Te, Ti, O+ and H+ varying with increase in solar activity. The strength of equinoctial asymmetry in Te and Ti is strong during early morning and daytime and strength decreases with increase in solar activity whereas during night time no asymmetry/weaker is observed in low/high solar activity respectively. During the day time, a very strong equinoctial asymmetry in O+ is observed during solar minimum which diminishes with increase in solar activity. The similar diurnal behaviour of H+ as that of O+ is observed during low solar activity but no clear equinoctial asymmetry is observed during solar maximum, as H+ being highly dynamic. The transition height (O+/H+) is lowest in early morning during solar minimum, which increases during local day-time. The rate of increase in transition height is different in both the equinoxes (higher in vernal than autumn) with respect to dependence on the solar activity, during daytime. Hence equinoctial asymmetry is stronger during solar minimum period than maximum, with higher/lower transition height in vernal during daytime/nighttime respectively.


      PubDate: 2014-06-14T18:17:08Z
       
  • New types of simple non-linear models to compute solar global irradiance
           from cloud cover amount
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): Viorel Badescu , Alexandru Dumitrescu
      Most simple solar radiation models are built with reference to a basic model calibrated for clear sky conditions. New models are built in this paper with reference to two basic models, calibrated for clear sky and overcast sky conditions, correspondingly. The models are illustrated with measurements data from five meteorological stations in Romania (South-Eastern Europe), where the ratio between the solar irradiance on overcast sky and clear sky, respectively, ranges between 0.27 and 0.55. A three-parameter model is used for both basic models. Three new types of regression models were developed from the two basic models. They are non-linear generalizations of the Angstrom–Savinov model. Their accuracy decreases by increasing the cloud cover amount. One model has been further tested. A set of regression coefficients has been obtained by fitting that model to all available data, for all stations. The model based on this set of regression coefficients has good accuracy in any particular station, when low and intermediate cloudy skies are considered. The model based on a set of regression coefficients obtained in a given station was tested in other stations. Its accuracy is good (or marginally, good enough) on skies with low and intermediate cloudy skies. Its accuracy is good for intermediate zenith angles, ranging between 30° and 70°.


      PubDate: 2014-06-14T18:17:08Z
       
  • Signatures of ultra fast Kelvin waves in low latitude ionospheric TEC
           during January 2009 stratospheric warming event
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): D.V. Phanikumar , K. Niranjan Kumar , Sanjay Kumar
      In this study, for the first time, planetary wave signatures in ionospheric Total Electron Content (TEC) retrieved from global positioning service (GPS), mesospheric wind and temperature at low latitude station has been identified during January–February 2009. Our investigations revealed that planetary waves with 3–5 days periodicity characterized as ultrafast Kelvin (UFK) waves caused by stratospheric warming event during January 2009. The UFK waves are observed to be propagated from lower atmosphere to ionosphere. The UFK perturbations during SSW event are discussed in the light of current understanding of role of non linear interaction of planetary waves to modulate low latitude ionosphere.


      PubDate: 2014-06-14T18:17:08Z
       
  • On the vertical distribution of carbon monoxide over Bay of Bengal during
           winter: Role of water vapour and vertical updrafts
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): I.A. Girach , Prabha R. Nair
      The differences in the spatial pattern of column carbon monoxide (CO) and in-situ measured near-surface CO over Bay of Bengal (BoB) during winter were examined in the light of vertical distribution of CO as retrieved from MOPITT (Measurements Of Pollution In The Troposphere) on board Terra spacecraft. The column CO showed relatively high values over southern-BoB whereas the near-surface CO showed low mixing ratio indicating the existence of significant amount of CO at higher altitudes. The vertical profiles of CO over the BoB region retrieved from MOPITT exhibit a high altitude peak around ~9km altitude region. The role of water vapour and convective activity/vertical updrafts in establishing the observed vertical profile of CO was investigated. It is found that CO got uplifted to the higher altitude due to updrafts and water vapour caused depletion of CO at lower altitudes which appeared as an apparent high in CO mixing ratio at higher altitude relative to that over lower altitude. The role of water vapour in the destruction of CO was confirmed by box model simulations. Airmass back-trajectory analysis showed that the long range transport from lower troposphere/boundary layer was also partially responsible for higher mixing ratios at higher altitude. In addition, a comparison of in-situ measured near-surface CO and those retrieved from MOPITT using retrieval algorithm Versions 4 and 5 showed that the points of discrepancy have reduced in the Version 5. Biomass burning and anthropogenic activities taking place over the Myanmar landmass was found to be responsible for the hot spots of near-surface-CO over the northeast-BoB.


      PubDate: 2014-06-14T18:17:08Z
       
  • A study on wind dynamics during convective processes using the
           Postset-beam-steering technique
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): V.K. Anandan , V.N. Sureshbabu , S. Vijayabhaskara Rao , Shridhar Kumar
      This paper demonstrates the potential of the Postset-beam-steering (PBS) technique on a VHF multi receiver profiler radar for studying convective processes over the Middle and Upper (MU) atmospheric radar located at Shigaraki (34.85°N, 136.10°E), Japan. During times of convection, it is difficult to study the atmospheric processes by normal radar observational methods due to instantaneous changes in the wind fields over the position and time. Meanwhile, it is important to know the simultaneous changes in vertical and horizontal wind fields for studying the evolution of atmospheric processes and the dynamics associated with it. PBS, as a means of software beam steering, overcomes such difficulties in estimating atmospheric wind parameters because of a number of inherent signal processing algorithms associated with the technique itself. The main objective of the present work includes major investigations of fast changing 3-D wind fields and the processes associated with it. Further, the advantages of the PBS for studying the spatial variability in winds, circulation patterns, mixing process, momentum flux and vorticity during the atmospheric convection are presented through a set of examples.


      PubDate: 2014-06-14T18:17:08Z
       
  • Transmission of planetary wave effects to the upper atmosphere through
           eddy diffusion modulation
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): Vu Nguyen , S.E. Palo
      Past observations have shown that the effects of planetary waves can travel beyond their dissipation region and into the thermosphere and ionosphere. One possible mechanism through which this event can occur is the modulation of turbulent mixing near the turbopause. Because turbulent mixing in the mesosphere–lower thermosphere is strongly dependent on the amount of wave dissipation, planetary wave filtering of gravity waves from below can indirectly modulate the amount of turbulent mixing. This study uses the NCAR TIE-GCM to investigate how this mechanism induces variability in upper atmospheric composition and density. It is shown that varying the amount of turbulent mixing at discrete planetary wave periods induces similar periodicities in neutral and electron density. This process is driven by species diffusive flux through isobaric (constant pressure) levels, resulting in atmospheric contraction or expansion. Results also indicate that the mechanism studied has a wave frequency dependence and is most effective for long period planetary waves.


      PubDate: 2014-06-14T18:17:08Z
       
  • Traveling planetary wave ionospheric disturbances and their role in the
           generation of equatorial spread-F and GPS phase fluctuations during the
           last extreme low solar activity and comparison with high solar activity
    • Abstract: Publication date: September 2014
      Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 117
      Author(s): A.J. de Abreu , P.R. Fagundes , M.J.A. Bolzan , M. Gende , C. Brunini , R. de Jesus , V.G. Pillat , J.R. Abalde , W.L.C. Lima
      This investigation studies traveling planetary wave ionospheric disturbance (TPWID) type oscillations on the modulation of the F region virtual height rise during the E×B electric field pre-reversal enhancement (PRE), near sunset hours. We also studied their role in the generation of equatorial spread F (ESF) and GPS phase fluctuations during periods of the last extreme low solar activity (LSA) of January 2009 to April 2010 ( F 10.7 ¯ = 73 ) . A comparison is made with periods of high solar activity (HSA) in 2003 and 2004 near equatorial region. The ionospheric irregularities investigated are medium (bottom-side) and large (plasma bubble) scales. Ionospheric F region oscillations with period of days are due to the TPWIDs, which play an important role in producing favorable or unfavorable conditions for equatorial ionospheric irregularities, changing the electron vertical profile and F region height. In this paper, we present simultaneous ionospheric sounding (ionosonde) and GPS vertical total electron content (vTEC) observations carried out near equatorial region (Palmas 10.2°S, 48.2°W) and low latitude region (São José dos Campos 23.2°S, 45.9°W; located under the southern crest of the equatorial ionospheric anomaly), Brazil. Observations show that the occurrence of fresh ESF during LSA and HSA and fresh GPS phase fluctuations at equatorial region follow the trend of day-to-day variations in the F region virtual height, which are due to electric field PRE modulated by TPWID wave like oscillations. During LSA, the altitude of 250km acts as a threshold height for the generation of fresh ionospheric irregularities, whereas during HSA, the threshold height is 300km. The observations also found a strong increase in the generation of fresh ionospheric irregularities from October 2009 to March 2010 during LSA and from September 2003 to March 2004 during the HSA. Furthermore, in LSA, the period of fresh ionospheric irregularities was less than during HSA, though both periods followed a similar seasonal pattern. In the low-latitude, we observed more ESFs than phase fluctuations because ionosonde is more sensitive than GPS. We also observed periods with and without day-to-day oscillations in the F region virtual height. The observations made by GPS stations and ionosondes in the equatorial region, for much of the period analyzed, presented similar results with regard to the generation of equatorial ionospheric irregularities. In the low latitude, some nights of January, February, October, and December 2009 also showed a similarity.


      PubDate: 2014-06-14T18:17:08Z
       
 
 
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