Abstract: Publication date: Available online 18 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Rahim Zain , Memon Akhtar Ali , Arain Muhammad Owais
K-indices have been produced and analyzed using two computer based methods for one-minute geomagnetic data from Sonmiani Geomagnetic Observatory (SON), located at 25.203° in latitude and 66.75° in longitude, for the period 2009–2011. The two methods used are Finnish Meteorological Institute (FMI) method and Adaptive Smoothing (AS) method. Solar quiet daily variation (Sq) and solar regular variation (Sr) curves are produced using FMI method and their comparison is drawn. Various statistical analyses have been carried out by comparing the K-indices obtained through AS method with other geomagnetic observatories having similar time zone and geomagnetic latitude aiming to validate our results. Resulting K-indices obtained from AS method are in a good match with nearby observatories irrespective of the K derivation method used for each of the observatories compared. Further, we have compared the K-indices obtained through AS and FMI methods and found the FMI has a tendency to shift the results to somewhat higher K-values than the AS method.
Abstract: Publication date: Available online 18 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Yoav Yair , Lior Rubanenko , Keren Mezuman , Gal Elhalel , Meidad Pariente , Maya Glickman-Pariente , Baruch Ziv , Yukihiro Takahashi , Tomohiro Inoue
During July-August 2011, Expedition 28/29 JAXA astronaut Satoshi Furukawa conducted TLE observations from the International Space Station in conjunction with the “Cosmic Shore” program produced by NHK. An EMCCD normal video-rate color TV camera was used to conduct directed observations from the Earth-pointing Cupola module. The target selection was based on the methodology developed for the MEIDEX sprite campaign on board the space shuttle Columbia in January 2003 (Ziv et al., 2004). The observation geometry was pre-determined and uploaded daily to the ISS with pointing options to limb, oblique or nadir, based on the predicted location of the storm with regards to the ISS. The pointing angle was rotated in real-time according to visual eyesight by the astronaut. We present results of 10 confirmed TLEs: 8 sprites, 1 sprite halo and 1 gigantic jet, out of <2 hours of video. Sprites tend to appear in a single frame simultaneously with maximum lightning brightness. Unique images (a) from nadir of a sprite horizontally displaced form the lightning light and (b) from oblique view of a sprite halo, enable the calculation of dimensions and volumes occupied by these TLEs. Since time stamping on the ISS images was accurate within 1s, matching with ELF and WWLLN data for the parent lightning location is limited. Nevertheless, the results prove that the ISS is an ideal platform for lightning and TLE observations, and careful operational procedures greatly enhance the value of observation time.
Abstract: Publication date: Available online 18 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Jie Zhu , Biqiang Zhao , Weixing Wan , Baiqi Ning
Ionogram traces with the F3 layer in different latitude do not always seem similar. In our work, we tend to describe morphological features of traces with the F3 layer in magnetic low-latitude region and near magnetic equator through the quantitative investigation of the diurnal variation and latitude dependence of two morphologically characteristic parameters - the foF2-to-foF3 ratio and the difference between h'F3 and h'F2 - in geomagnetically quiet period. The distribution of two formation patterns (pattern A and pattern B are defined with increasing F3 peak density and with nearly constant or decreasing F3 peak density respectively as the peak moving upward around the onset of the F3 layer's occurrence) of the F3 layer is also investigated based on statistics of formation patterns of the F3 layer in Sanya and Kwajalein in 2011. The ideal equinoctial distribution (without the summer-to-winter neutral wind) of those patterns is symmetrical about magnetic equator with pattern A in magnetic low-latitude region and pattern B near magnetic equator. When taking the summer-to-winter neutral wind which helps plasma resist (enhance) diffusion to higher latitude in the windward (leeward) into consideration in a solstice, pattern A could be observed near magnetic equator in summer hemisphere and pattern B in magnetic low-latitude region in winter hemisphere compared with the ideal distribution in the equinox.
Abstract: Publication date: Available online 18 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): A.V. Pavlov , N.M. Pavlova
We present a comparison of the E-layer peak electron number densities, NmE, measured by the Boulder ionosonde during geomagnetically quiet conditions on 10 April 1996 at low solar activity, 2 April 1993 and 9 April 1978 during moderate solar activity conditions, and 10 April 1991 at high solar activity with numerical theoretical model calculations of NmE. Based on this comparison, the EUVAC model solar flux is necessary to increase by a factor of 2 at moderate and high solar activity in the wavelength range of 3.2–7.0nm. If O+(4S), O+(2D), O+(2P), and N+ ions are not calculated, the value of NmE is decreased up to a factor of 1.12 at solar minimum and up to a factor of 1.23 for the moderate and high solar activity conditions. The production of N2 + ions by photoelectron-impact ionization of N2 increases the value of NmE up to a factor of 1.18 at low solar activity and up to a factor of 1.33 for the moderate and high solar activity levels. The increase in NmE due to the production of O2 + ions by photoelectron-impact ionization of O2 does not exceed 4%. A difference between the calculated electron, Te, and neutral, Tn, temperatures is less than 1, 4, 20, 70, and 145K at 105, 110, 120, 130, and 140km altitude, respectively. Changes in NmE caused by this difference between Te and Tn are negligible.
Abstract: Publication date: Available online 16 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): I.B. Ievenko , V.N. Alexeyev , S.G. Parnikov
It is well known that the 630.0nm nightglow emission intensity at mid latitudes increased more than twofold in periods of maximum sunspot activity. It is assumed that this phenomenon is caused by variations in solar ultraviolet radiation intensity in solar activity cycles (Fishkova, 1983). In this paper, we present the results of photometric measurements of the nightglow emission intensity at 63°N and 130°E (Yakutsk) in 1990–2007. Moreover, we show the dependence of the 630.0nm emission intensity in magnetically quiet days on solar activity in the 22nd and 23rd cycles. It was established that there is a close relationship between the 630.0nm line nightglow intensity and the solar extreme ultraviolet (EUV) intensity based on SOHO/SEM data, obtained in 1997–2007 with a correlation coefficient of 0.8–0.9. The changes of ionization level of nighttime F2 layer at the Yakutsk station and neutral composition of the upper atmosphere (thermosphere) during the photometric observations have been analyzed. It is shown that the long-term variations of the red line emission intensity are caused by the change of nighttime F2 layer electron density. The nighttime ionization level is related to the electron density of the daytime F2 region which depends on the EUV flux intensity during a solar activity cycle.
Abstract: Publication date: Available online 17 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): R. Pradipta , L.A. Rooker , L.N. Whitehurst , M.C. Lee , L.M. Ross , M.P. Sulzer , S. Gonzalez , C. Tepley , N. Aponte , B.Z. See , K.P. Hu
We report a series of experiments conducted at Arecibo Observatory in the past, aimed at the investigation of 40.75kHz whistler wave interactions with ionospheric plasmas and the inner radiation belts at L=1.35. The whistler waves are launched from a Naval transmitter (code-named NAU) operating in Aguadilla, Puerto Rico at the frequency and power of 40.75kHz and 100kW, respectively. Arecibo radar, CADI, and optical instruments were used to monitor the background ionospheric conditions and detect the induced ionospheric plasma effects. Four-wave interaction processes produced by whistler waves in the ionosphere can excite lower hybrid waves, which can accelerate ionospheric electrons. Furthermore, whistler waves propagating into the magnetosphere can trigger precipitation of energetic electrons from the radiation belts. Radar and optical measurements can distinguish wave-wave and wave-particle interaction processes occurring at different altitudes. Electron acceleration by different mechanisms can be verified from the radar measurements of plasma lines. To facilitate the coupling of NAU-launched 40.75kHz whistler waves into the ionosphere, we can rely on naturally occurring spread F irregularities to serve as ionospheric ducts. We can also use HF wave-created ducts/artificial waveguides, as demonstrated in our earlier Arecibo experiments and recent Gakona experiments at HAARP. The newly constructed Arecibo HF heater will be employed in our future experiments, which can extend the study of whistler wave interactions with the ionosphere and the magnetosphere/radiation belts as well as the whistler wave conjugate propagation between Arecibo and Puerto Madryn, Argentina.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): N. Kleimenova , O. Kozyreva , S. Michnowski , M. Kubicki
The variations of the vertical atmospheric electric field (Ez) represent the state of the global atmospheric electric circuit, which is controlled by the world thunderstorm activity and by magnetosphere–ionosphere disturbances as well. Here we present a synthesis of our main results of the effects of the geomagnetic disturbances on the Ez variations, measured at the Earth′s surface at high and middle latitudes, which were previously published by Kleimenova et al. (2008, 2010). We studied the high latitude geomagnetic substorm effects on the Ez variations on the base of the continue Ez registrations at the polar station Hornsund (Spitsbergen). This station can map into the polar cap, auroral oval or near the border between these structures in dependence on the local time and the level of the geomagnetic activity. The high-latitude Ez variations associated with the substorm activity have been established. It was found that the Ez deviations were positive (Ez values increase) in the local morning and negative ones (Ez values decrease) in the local evening. We speculate that the direction of the Ez excursion depends on the station location relative to the positive or negative vortex of the polar ionospheric plasma convection. The Ez variations at the mid-latitude station Świder (near Warsaw) have been studied during 14 magnetic storms. To avoid the meteorological influences on the Ez measurements we used only the Ez data, obtained under the “fair weather” conditions. For the first time the main phase effect of all mentioned above magnetic storms was established in the mid-latitude atmospheric electricity variations. The strong daytime Ez negative excursions (Ez value decreases) were found in association with the simultaneous night-side magnetospheric substorm developing during the studied magnetic storms. The considered Ez deviations could be results an interplanetary electric field penetration into the magnetosphere. Another plausible reason could be related to the common ionosphere conductivity increasing due to substorm energetic electron precipitation, modifying the high-latitude ionospheric part of the global atmospheric electric circuit.
Highlights ► The effects of substorms in the high-latitude atmospheric Ez variations were found. ► The sign of Ez deviations was controlled by the sign of the ionospheric convection. ► The magnetic storm influence on the day mid-latitude Ez variations was established.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): I.V. Golovchanskaya , B.V. Kozelov , I.V. Despirak
Physical mechanism of the broadband ELF (BB ELF) turbulence observed in the topside ionosphere is not fully understood as yet. One feature that could, to a certain extent, shed light on its physics is a seasonal variation in the BB ELF electric fields at frequencies up to several hundred Hz (or higher) in the spacecraft frame. Specifically, the electric fields are several times enhanced in winter season compared to summer season. Such seasonal asymmetry was first reported by Heppner et al. (1993) for the AC electric fields measured by the Dynamics Explorer 2 (DE-2) satellite at altitudes from 300km to 900km. Here we demonstrate this effect by electric field observations of the FAST satellite (altitudes up to 4000km) with a sample rate of 512s−1 and discuss its implications for the involved generation mechanism of the BB ELF fields.
Highlights ► Seasonal asymmetry in the BB ELF electric fields is demonstrated by FAST data. ► Seasonal effect is present in both Alfvénic turbulent E-fields and electrostatic noise. ► Seasonal asymmetry in the Alfvénic turbulence can be explained in quasi-static models. ► Electrostatic noise excited by E-fields of Alfvénic turbulence is season dependent.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Finn Søraas , Marita Sørbø
Observations of Energetic Neutral Atoms (ENAs) emitted from the proton aurora and from the equatorial ring current at tens to a few hundred of keV during the Halloween 2003 storm are presented. From the proton oval a large number of ENAs are spread over the polar cap making a contribution to the ion outflow. From the Ring Current (RC) ENAs are spread in all directions. The Storm Time Equatorial Belt (STEB) consists of ENAs observed around the geomagnetic equator at low L-values. Their source is RC protons existing at larger L-values. The number of observed ENAs is directly dependent on the amount of ions (protons) present in the RC along the line of sight. Thus the time variations of the STEB enable us to monitor the behavior of the RC. Based on observations of the STEB at six different local times we discuss the RC injection region, the drift of RC-particles through the evening/afternoon sector into the morning sector and the RC decay time during the storm recovery phase. The MLT variation of the STEB gives information about the symmetry and asymmetry of the RC with no interference from other current systems. The revealed RC-symmetry and asymmetry complement magnetic ground observations.
Highlights ► We study low altitude observations of energetic neutral atoms both from the proton aurora and from the ring current. ► The low altitude equatorial belt of ENA, the STEB, exhibits the same local time asymmetry as the ring current. ► The time variation of the STEB enables us to monitor the total amount of ions in the ring current.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): R. Ilie , R.M. Skoug , H.O. Funsten , M.W. Liemohn , J.J. Bailey , M. Gruntman
Long-term ring current decay following a magnetic storm is mainly due to charge exchange collisions of ring current ions with geocoronal neutral atoms forming energetic neutral atoms (ENAs) that leave the ring current system. Therefore, the density distribution of these cold and tenuous neutral hydrogen atoms plays a key role in the ring current recovery. TWINS ENA images provide a direct measurement of these ENA losses and therefore insight into the dynamics of the ring current decay through interactions with the geocorona. To assess the influence of geocoronal neutrals on ring current decay, we compare the predicted ENA emission using five different geocoronal models and the HEIDI ring current model to simulate the July 22, 2009 storm. We show that for high energy H + ( ≥ 100 keV ) , all geocoronal models predict similar decay rates of the ring current ions. However, for low energy ions ( ≤ 100 keV ), the decay rate varies significantly depending on the geocoronal density model. Comparison with TWINS ENA images shows that the location of the peak ENA enhancements is highly dependent on the distribution of geocoronal hydrogen density. The ring current topology depends greatly on the hydrogen model used, therefore knowing the H-distribution is very important in understanding how the ring current recovers following a magnetic storm.
Highlights ► For high energy H+ ions all geocoronal H models predict similar decay rates. ► For low energy ions, the decay rate varies significantly between the models. ► The decay rate of ring current ions is pitch angle dependent. ► Ions that bounce farther decay faster yielding higher ENA fluxes closer to Earth. ► Synthetic ENA images are very sensitive to the geocoronal H density distribution.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): E.E. Antonova , I.P. Kirpichev , V.V. Vovchenko , M.V. Stepanova , M.O. Riazantseva , M.S. Pulinets , I.L. Ovchinnikov , S.S. Znatkova
There are strong experimental evidences of the existence of plasma domain forming a closed plasma ring around the Earth at geocentric distances ∼7–10R E . In this work, we analyze the main properties of this ring, using the data of the THEMIS satellite mission, acquired between April 2007 and September 2011. We also analyze the contribution of this ring to the storm dynamics. In particular, it is shown that the distribution of plasma pressure at ∼7–10R E is nearly azimuthally symmetric. However, the daytime compression of the magnetic field lines and the shift of the minimal value of the magnetic field to higher latitudes lead to the spreading of the transverse current along field lines and splitting of the daytime integral transverse current into two branches in Z direction. The CRC is the high latitude continuation of the ordinary ring current (RC), generated by plasma pressure gradients, directed to the Earth. We evaluated the contribution of the azimuthally symmetric part of the plasma ring to the Dst index for strong geomagnetic storms using the AMPTE/CCE radial profiles of plasma pressure published before, and showed that the contribution of the ring current including both RC and CRC is sufficient to obtain the observed Dst variation without the necessity to include the tail current system.
Highlights ► We demonstrate the existence of the plasma ring surrounding the Earth. ► We obtain the distribution of plasma pressure in the ring using THEMIS data. ► We analyze the distribution and structure of transverse currents in the ring. ► We model the contribution of the symmetric part of the ring current to Dst.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Michael W Liemohn , Darren L De Zeeuw , Natalia Yu Ganushkina , Janet U Kozyra , Daniel T Welling
The cross-field current systems within a global, coupled geospace simulation of the January 6, 2011 high-speed stream-driven interval are analyzed to understand the flow and partitioning of energy within the magnetosphere. Even though this is a small storm with a minimum Dst of −41nT, it is shown that the time-dependence of current system locations is very similar to that from a much larger storm (minimum Dst of −230nT) driven by an interplanetary coronal mass ejection. That is, during the early part of the main phase, the tail current inner edge moves Earthward inside of geosynchronous orbit, but then retreats during the later part of the main phase, and by the peak of the storm interval, the ring/tail boundary is beyond L=10 in the nightside magnetosphere. It is also seen that a banana current (the part of the partial ring current that does not close through the ionosphere but rather with itself by flowing around the pressure peak entirely on the nightside) accounts for nearly all of the eastward current and the innermost portion of the westward current in the equatorial plane throughout the storm main phase interval.
Highlights ► Analysis of currents from a coupled model simulation during a weak CIR/HSS storm. ► Dominant currents are tail and banana in early main phase, and symmetric ring at the peak. ► Current system locations are remarkably similar to a much larger ICME-driven storm
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Rumen Shkevov , Nikolay Sergeevich Erokhin , Ludmila Anatolievna Mikhailovskaya , Nadezhda Nikolaevna Zolnikova
A theoretical study of the efficiency of the relativistic acceleration of charged particles by a finite amplitude electromagnetic wave packet in space plasma is presented. The effect of surfatron mechanism particle acceleration is investigated by numerical analysis of the second-order, non-stationary, nonlinear equation for the wave packet phase at the particle trajectory. The influence of the phase and group velocities of the wave packet at the wave packet carrying frequency on the acceleration efficiency is studied. The optimal conditions for weakly relativistic particles captured by electromagnetic wave packets with the following highly relativistic charge acceleration are determined. The particle energy growth rate for the regime of surfatron relativistic acceleration is determined. The temporal dynamics of particle acceleration are investigated. The conclusion about the possibilities of ultrarelativistic surfatron acceleration of charges by a wave packet with a smooth amplitude envelope is given.
Highlights ► A theoretical study of the relativistic acceleration of charged particles is presented. ► Surfatron mechanism of particle acceleration is investigated by the numerical analysis. ► Efficiency of the charged particle relativistic acceleration is studied. ► Ultrarelativistic charges experiencing surfatron acceleration by a wave packet are analyzed. ► The particle energy growth rate is determined.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): X. Tao , J. Bortnik , J.M. Albert , R.M. Thorne , W. Li
The effects of amplitude modulation on nonlinear interactions between a parallel propagating whistler wave and electrons in a dipole field are investigated in this work using a test particle code. Here we first use the test particle simulation to validate a previous single-wave nonlinear theory. Then we adopt a simple two-wave model to represent the recently observed amplitude modulation of a whistler wave field. By varying the frequency spacing between the two waves, we investigate the effects of different modulation frequencies on the nonlinear interactions. We demonstrate that when the resonance overlap condition is satisfied, the resulting change in the electron pitch angle and energy could be very different from what has been predicted by ideal single-wave nonlinear theories. Using a previously observed probability distribution of the subpacket modulation frequency of a chorus event, we obtain the probability distribution of different types of electron response. Our results indicate that the observed subpacket distribution produces particle responses in both non-overlapping and overlapping regimes. Our results suggest that the observed amplitude modulation should be considered when quantitatively treating interactions between electrons and recently observed large amplitude whistler waves or chorus waves.
Highlights ► We consider the effects of amplitude modulation on nonlinear interactions. ► We demonstrate three interaction regimes using the resonance overlap condition. ► We evaluate the importance of chorus subpackets on nonlinear interactions. ► The amplitude modulation should be considered in nonlinear interactions.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): A.G. Yahnin , T.A. Yahnina , H. Frey , V. Pierrard
Sub-oval proton auroras discovered by the IMAGE spacecraft correlate with EMIC waves (geomagnetic pulsations of the Pc1 range). This means that a common source of the waves and proton precipitation is the ion-cyclotron (IC) instability developing in the vicinity of the equatorial plane. Different forms of the proton auroras reflect different regimes of the IC instability and different conditions in the near-Earth equatorial magnetosphere. To understand what are the conditions for the generation of the sub-oval proton aurora one may map the aurora onto the equatorial plane and compare the projection with some important magnetospheric boundaries. In this report we compare the projection of so-called “proton aurora spots” with the location of the plasmapause. The latter is determined by the plasmapause formation model based on the quasi-interchange instability mechanism. The comparison shows that often the proton aurora spot source is located in the vicinity of the plasmapause or in the cold plasma gradient inside the plasmapause. In some events, the proton aurora spots map well outside the plasmapause. We assume that in the latter case the IC instability develops when westward drifting energetic protons interact with the cold plasma that was earlier detached from the plasmasphere.
Highlights ► We map sub-oval proton aurora spots observed with IMAGE onto the equatorial plane. ► We model the plasmapause location on the basis of the Lemaire's theory. ► Most of the proton aurora spots are mapped into the vicinity of plasmapause.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): F. Darrouzet , J. De Keyser
The purpose of this paper is to review recent advances in the study of the Earth's plasmasphere. Most of these have been obtained with data from two missions launched in 2000, Cluster and IMAGE. Indeed, those missions have deeply modified our understanding of this region due to their specificity: Cluster is a 4-spacecraft mission and IMAGE a global imaging mission, both types studying the plasmasphere for the first time. We review here some results of recent studies of the global evolution of the plasmasphere under the increase of the geomagnetic activity: plasmaspheric erosion, evolution of the plasmapause, plasmaspheric plumes, modification in the plasmaspheric corotation, refilling of the plasmasphere and evolution towards a smooth plasmasphere during prolonged quiet period. We also review results on plasmaspheric waves, which are formed and propagate at all stages of plasmaspheric evolution.
Highlights ► Review some results of recent studies about the plasmasphere. ► Study the global evolution of the plasmasphere under increase of geomagnetic activity. ► Review some recent results on plasmaspheric waves.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): M. Ugai
So-called plasmoids are most fundamental signatures of geomagnetic substorms, and precise measurements of magnetic fields have been obtained by in situ satellite observations. Hence, in understanding substorm phenomena, it is essential to clarify the physical mechanism of plasmoid dynamics. The present paper studies on the basis of the spontaneous fast reconnection model how a large-scale plasmoid is generated and propagates in weakly sheared current sheets. It is demonstrated that the basic structure and dynamics of the plasmoid, generated by the fast reconnection, are both qualitatively and quantitatively in good agreement with actual satellite observations. In particular, magnetic field lines inside the generated plasmoid deviate from a helical geometry.
Highlights ► We apply the fast reconnection to plasmoids in the geotail. ► Magnetic field lines inside the plasmoid is not helical. ► Plasmoids can be generated as a plasma sheet bulge. ► The plasmoid structure is in good agreement with observations.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): M. Palmroth , I. Honkonen , A. Sandroos , Y. Kempf , S. von Alfthan , D. Pokhotelov
Global magnetohydrodynamic (MHD) simulations have been successful in describing systems where the important spatial scales are larger than ion inertial length and the plasma has a well-defined temperature. The weakness of global one-fluid MHD simulations is their inability to model the multi-temperature, multi-component plasmas in the inner magnetosphere, where most of space-borne technology, including communication and navigation systems reside. We are developing a global hybrid-Vlasov simulation, where electrons are MHD fluid, but protons are modeled as distribution functions evolved in time using the Vlasov equation. This approach does not include the noise present in kinetic-hybrid simulations, but is computationally extremely challenging requiring petascale computations with thousands of cores. Here, we briefly review the status of our new parallel six-dimensional Vlasov solver. We carry out a test particle simulation and propagate the distribution functions using the electromagnetic fields of the GUMICS-4 global MHD simulation. Our main goal is to test the Vlasov solver in a global setup against the standalone GUMICS-4 global MHD simulation. The results shown here are obtained during due northward interplanetary magnetic field (IMF). We find that the magnetosheath and magnetopause plasma properties from the test particle simulation are in rough agreement with the results from the GUMICS-4 simulation. Furthermore, we show that the cusp injection patterns reproduce the expected behavior of northward IMF. The results indicate that our solver behaves sufficiently well, indicating that global hybrid-Vlasov simulations of this kind are feasible, promising improved global simulation capabilities in the future.
Highlights ► We show the first result of a new global beyond-MHD six-dimensional hybrid-Vlasov simulation. ► The solver reproduces the main characteristics of the magnetosheath and bow shock. ► Cusp injection patterns reproduce the expected behavior of northward IMF.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): T.E. Moore , J.L. Burch , W.S. Daughton , S.A. Fuselier , H. Hasegawa , S.M. Petrinec , Zuyin Pu
We review recent experience from the Cluster, Double Star, and THEMIS missions for lessons that apply to the upcoming Magnetospheric Multiscale Mission (MMS) being developed for launch in 2014. On global scales, simulation and statistical studies lead to mean configurations of dayside reconnection, implying specific relative alignments of the inflow magnetic fields and X-line, with implications for MMS operations designed to maximize the number of close encounters with the diffusion region. At intermediate MHD-to-ion scales, reconstruction of features created by one or two X-lines have developed to the point where data from a cluster of spacecraft can determine their temporal trends and the approximate three-dimensional X-line structure. Recent petascale particle-in-cell (PIC) simulations of reconnection encompass three spatial dimensions with excellent resolution, and make striking predictions of electron scale physics that creates complex interacting flux ropes under component reconnection. High time resolution measurements from MMS will determine the detailed electron scale kinetics embedded within the global and MHD–ion scale contexts. These developments will lead to the refinement of our three-dimensional multiscale picture of reconnection, yielding improved understanding of the global, MHD, and local physics controlling the onset or quenching, variability, and mean rate of reconnection. This in turn will enable improved predictability of the structural features created by transient reconnection, and their space weather consequences.
Highlights ► We review new capabilities for study of dayside reconnection across all scales. ► The distribution of flank reconnection will be settled by MMS Phase 1 operations. ► Advances in MHD reconstruction should permit 3D structure inferences from MMS data. ► Striking predictions of electron scale physics will be tested by MMS measurements.
Abstract: Publication date: August 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 100–101
Author(s): Byoung-Kwon Park , Song-You Hong
The skill of medium-range forecasting can be determined by the quality of the initial conditions through data assimilation, model dynamics, and physics. In this study, the roles of physics packages in global forecasting systems are evaluated on a medium-range forecast testbed. Two physics packages are evaluated: The standard physics package in the model is a version of the National Centers for Environmental Prediction (NCEP) global forecast system, which has been employed to produce the NCEP/Department of Energy (DOE) reanalysis. The revised package consists of schemes accounting for radiation, the planetary-boundary layer, the land-surface model, gravity wave drag, and moist convection. Evaluations were performed in August 2010 and January 2011, focusing on the 500-hPa geopotential height and precipitation. The results show that the revised physics package improved the performance of the 500-hPa geopotential height throughout the 10-day forecast period. The improvement is larger in the southern hemisphere than in the northern hemisphere after the 5-day forecast, with a more distinct enhancement in the winter hemisphere. The skill of the precipitation forecasts shows overall improvement, although too much suppression of heavy precipitation needs to be rectified. The cumulus parameterization scheme is found to be a critical factor in improving the large-scale flow, but revisions in other processes, such as the mutual compensation effects among physics algorithms, need to be considered.
Abstract: Publication date: Available online 14 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): S.H. Mthembu , V. Sivakumar , N.J. Mitchell , S.B. Malinga
In this study, we report the interaction of planetary waves and tides observed in the mesosphere/lower thermosphere (MLT) region using a meteor radar located at Rothera (68°S, 68°W) Antarctica. The study has been conducted using wind data collected over the year 2005. The obtained data are subjected to wavelet analysis to determine the spectral content of the data and it was found that the MLT region is dominated by semidiurnal tide (SDT) and planetary waves with periods around 5, 10, 16 and 23 days. The behaviour of the semidiurnal tide was investigated and found to be very variable and modulated at the period of ∼23 days in the zonal component and at ∼5 and 16 days in meridional component. Non-linear interaction between the SDT and 16-day planetary wave in the meridional component was found to be mostly responsible for the variability of the SDT than the interaction between the SDT and 5 day in the meridional component and between the SDT and 23-day planetary wave in the zonal component. This was established by investigating the validity of frequency, phase and wavenumber relationship.
Abstract: Publication date: Available online 14 May 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Carsten Schmidt , Kathrin Höppner , Michael Bittner
We present a new spectrometer with high temporal resolution for the observation of OH Meinel band emission dynamics in the spectral range between 1.5µm and 1.6µm. The instrument was developed and is now in operation at the German Remote Sensing Data Center (DFD) of the German Aerospace Center (DLR) in Oberpfaffenhofen (11.27°E, 48.08°N), Germany - a measurement station of the international Network for the Detection of Mesosphere Change (NDMC). It is equipped with a thermoelectrically cooled 512 element InGaAs-photodiode array (PDA) and a polychromator with a grating blazed for 1.6µm. During routine operation one spectrum is obtained every 15seconds, originating from a field of view of approximately 15°×15° corresponding to~24×24km2 in 87km height, the peak height of the OH emission layer. The covered wavelength range allows the observation of the OH(3-1) Q- and P-branches as well as of the OH(4-2) R- and Q-branches. Rotational temperatures are calculated using OH(3-1) P-branch emissions between 1.52µm and 1.55µm. Being the successor of the older scanning grating spectrometers of the GRIPS type it is named GRIPS 6 (Ground-based Infrared P-branch Spectrometer). A fully automated data acquisition and analysis scheme has also been developed, that covers the complete processing chain from data recording to derivation of rotational temperatures and to long-term archiving. For the estimation of a nocturnal mean value all samples of the nightly temperature time series are weighted according to their individual precision. Thus, mean temperatures are between 1 and 2K lower compared to the unweighted arithmetic mean. Data products are archived at the World Data Center for Remote Sensing of the Atmosphere (WDC-RSAT) and results are displayed at the website of the Network for the Detection of Mesosphere Change (NDMC). A summary of the data obtained during the first 40 months of operation at the German Remote Sensing Data Center as well as aspects of data processing efforts are presented.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): J. Semkova , R. Koleva , St. Maltchev , N. Bankov , V. Benghin , I. Chernykh , V. Shurshakov , V. Petrov
The Liulin-5 charged particle telescope observes the radiation characteristics in the spherical tissue-equivalent phantom of MATROSHKA-R international project on the International Space Station (ISS). Liulin-5 measures time resolved deposited energy spectra, linear energy transfer (LET) spectrum, flux and absorbed dose rates for electrons, protons and the biologically relevant heavy ion components of the cosmic radiation at three depths along the phantom's radius. We present some new results of Liulin-5 experiment obtained from June 2007 to March 2010. The average quality factor for different time intervals is between 2.7 and 4.4. Due to the heavy ions in LET spectrum of the galactic cosmic rays (GCR), the GCR quality factor is bigger than that of the trapped protons. The absorbed dose rates measured at depths in the phantom corresponding to the depths of blood forming organs in human body are 7.75–9.6μGy/h and the dose equivalent rates are 24.6–36.7μSv/h. Usually the trapped protons contribute about 60% of the total absorbed dose at 40mm depth in the phantom and about 40% at 165mm depth. The rest of the dose comes from GCR. Space Shuttle docking and the change of ISS attitude preformed for that purpose lead to a decrease in the total doses and to decreasing the trapped protons contributions. The doses from GCR are not affected neither by the depth of measurement not by Shuttle docking. At 165mm depth in the phantom the largest fluxes along the ISS orbit are obtained from the trapped protons in the South Atlantic Anomaly (SAA) at L values 1.26–1.27, B∼0.198Gs, geographical longitude ∼−51° to −55°, latitude ∼−28° to −29° and altitudes 361–363km. Minimal values about 0.1 particles/cm2s were recorded at L∼1 from GCR, at L≥4 the GCR flux reaches 2.1 particles/cm2s.
Highlights ► Liulin-5 measured radiation characteristics in the spherical phantom on ISS during solar cycle 23 minimum. ► Dose rates at 40–60mm phantom's depth are 7.75–9.6μGy/h, dose equivalent rates are 24.6–36.7μSv/h. ► Usually SAA protons contribute ∼60% of the total absorbed dose at 40mm and ∼40% at 165mm phantom's depth. ► Shuttle docking and ISS attitude change by 180° cause decrease in dose rates in SAA. ► A detailed mapping of the particle flux distribution along the ISS orbit is done.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Ts.P. Dachev , B.T. Tomov , Yu.N. Matviichuk , Pl.G. Dimitrov , N.G. Bankov , G. Reitz , G. Horneck , D.P. Häder , M. Lebert , M. Schuster
The paper presents observations of relativistic electron precipitations (REP) on the International Space Station (ISS) obtained by three Bulgarian-built instruments flown in 2001 and 2008–2010. The first data are from the Liulin-E094 instrument flown in May–August 2001 inside the US laboratory module of the ISS. Next the time profiles of the REP-generated daily fluences and the absorbed doses at the orbit of ISS during the period February 2008–August 2010 are analyzed in dependence of the daily Ap index and compared with the daily relativistic electron fluence with energies of more than 2MeV measured by the GOES. The REP in April 2010 being the second largest in GOES history (with a >2MeV electron fluence event) is specially studied.
Highlights ► We report observations of relativistic electrons on ISS. ► Data are obtained by Bulgarian build Liulin type instruments. ► It is obtained that relativistic electrons on ISS are common phenomena.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Ilan Roth
The analogy between magnetohydrodynamics (MHD) and knot theory is utilized in presenting a new method for an analysis of stability and evolution of complex magnetic heliospheric flux tubes. Planar projection of a three-dimensional magnetic configuration depicts the structure as a two-dimensional diagram with crossings, to which one may assign mathematical operations leading to robust topological invariants. These invariants enrich the topological information of magnetic configurations beyond helicity. It is conjectured that the field which emerges from the solar photosphere is structured as one of the simplest knots—unknot or prime knot—and these flux ropes are then stretched while carried by the solar wind into the interplanetary medium. Preservation of invariants for small diffusivity and large cross section of the emerging magnetic flux makes them impervious to large scale reconnection, allowing us to predict the observed structures at 1AU as elongated prime knots. Similar structures may be observed in magnetic clouds which got disconnected from their footpoints and in ion drop-out configurations from a compact flare source in solar impulsive solar events. Observation of small scale magnetic features consistent with prime knots may indicate spatial intermittency and non-Gaussian statistics in the turbulent cascade process. For flux tubes with higher resistivity, magnetic energy decay rate should decrease with increased knot complexity as the invariants are then harder to be violated. These observations could be confirmed if adjacent satellites happen to measure distinctly oriented magnetic fields with directionally varying suprathermal particle fluxes.
Highlights ► New magnetic field classification by merging knot theory with MHD is proposed. ► Invariants for the configuration and evolution of magnetic fields are specified. ► Prime knots are suggested as building blocks of magnetic configurations. ► Solar wind field and small-scale current sheets structures are conceived as knots.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): C.J. Farrugia , N.V. Erkaev , V.K. Jordanova , N. Lugaz , P.E. Sandholt , S. Mühlbachler , R.B. Torbert
The interaction of interplanetary coronal mass ejections (ICMEs) and magnetic clouds (MCs) with the Earth's magnetosphere exhibits various interesting features principally due to interplanetary parameters which change slowly and reach extreme values of long duration. These, in turn, allow us to explore the geomagnetic response to continued and extreme driving of the magnetosphere. In this paper we shall discuss elements of the following: (i) anomalous features of the flow in the terrestrial magnetosheath during ICME/MC passage and (ii) large geomagnetic disturbances when total or partial mergers of ICMEs/MCs pass Earth. In (i) we emphasize two roles played by the upstream Alfvén Mach number in solar wind–magnetosphere interactions: (i) It gives rise to wide plasma depletion layers. (ii) It enhances the magnetosheath flow speed on draped magnetic field lines. (By plasma depletion layer we mean a magnetosheath region adjacent to the magnetopause where magnetic forces dominate over hydrodynamic forces.) In (ii) we stress that the ICME mergers elicit geoeffects over and above those of the individual members. In addition, features of the non-linear behavior of the magnetosphere manifest themselves.
Highlights ► ICME-magnetosphere interactions: key player is the low Alfven Mach number. ► Magnetosheath is a low-beta region in this case. ► Accelerated flows occur on draped field lines. ► ICME Interactions lead to intensified magnetopspheric disturbances. ► A 2-step great storm due to one such interaction.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Robert L. McPherron , Daniel N. Baker , T.I. Pulkkinen , T.-S. Hsu , J. Kissinger , X. Chu
Geomagnetic activity depends on a variety of factors including solar zenith angle, solar UV, strength of the interplanetary magnetic field, speed and density of the solar wind, orientation of the Earth’s dipole, distance of the Earth from Sun, occurrence of CMEs and CIRs, and possibly other parameters. We have investigated some of these using state-dependant linear prediction filters. For a given state a prediction filter transforms a coupling function such as rectified solar wind electric field (VBs) to an output like the auroral electrojet index (AL). The area of this filter calculated from the sum of the filter coefficients measures the strength of the coupling. When the input and output are steady for a time longer than the duration of the filter the ratio of output to input is equal to this area. We find coupling strength defined in this way for Es=VBs to AL (and AU) is weakest at solar maximum and strongest at solar minimum. AL coupling displays a semiannual variation being weakest at the solstices and strongest at the equinoxes. AU coupling has only an annual variation being strongest at summer solstice. AL and AU coupling also vary with time relative to a stream interface. Es coupling is weaker after the interface, but ULF coupling is stronger. Total prediction efficiency remains about constant at the interface. The change in coupling strength with the solar cycle can be explained as an effect of more frequent saturation of the polar cap potential causing a smaller ratio of AL to Es. Stronger AL coupling at the equinoxes possibly indicates some process that makes magnetic reconnection less efficient when the dipole axis is tilted along the Earth–Sun line. Strong AU coupling at summer solstice is likely due to high conductivity in northern summer. Coupling changes at a stream interface are correlated with the presence of strong wave activity in ground and satellite measurements and may be an artifact of the method by which solar wind data are propagated.
Highlights ► We use state-dependent linear prediction filters to model Es–AL coupling. ► Coupling strength is weakest at maximum of solar cycle and weakest at minimum. ► Es–AL coupling is strongest at equinoxes and weakest at solstices. ► Es–AU coupling is strongest at summer solstice. ► Es coupling is weaker after a solar wind stream interface than before.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): K. Chakarova , V. Rusanov , A.X. Trautwein
The iron-bearing compounds in manganese deep sea sediments (nodules and crusts) are studied by Mössbauer spectroscopy at 77, 4.2 and 0.3K. The Mössbauer parameters and the concentration of the two main components α-FeOOH (goethite) and Fe5HO8·4H2O (ferrihydrite), are measured in 1mm sampling steps. The mineral goethite exhibits defect crystal structure. It shows a Mössbauer sextet with broad and asymmetric lines at 77K and at room temperature partially a doublet due to superparamagnetic state. Ferrihydrite has a very low blocking temperature (<20K) and in our measurements at 0.3K, shows a Mössbauer sextet with broad lines. X-ray topography images of Fe–Mn nodules and crusts reveal a specific layer structure related to two long-period variations—1.9 million years (Ma) of the eccentricity e and 1.2Ma of the obliquity ε of Earth's axis, respectively. According to the Milankovitch astronomical theory they can enforce drastic changes of climate. The hydrogenous Fe–Mn nodules and crusts have a very low growth rate of 2–10mm/Ma, while the diagenetic nodules grow faster, 10–50mm/Ma. So time intervals up to 20Ma could be covered. Some global geological events such as the rise of the Isthmus of Panama and the beginning of the modern bottom water circulation (about 6.4Ma before present) have changed the crusts structure and have been discussed. Some specific boundaries in the layer structure of nodules are easily identified. This allows a quick initial self-dating of the nodules without the use of expensive isotopic radiometric methods of dating.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): Rolf Werner , Dimitar Valev , Atanas Atanassov , Veneta Guineva , Andrey Kirillov
Daily time series of the NO2 slant column amounts obtained by the GASCOD-BG instrument at Stara Zagora and by instruments at European NDACC stations near 40°N and of two subtropical stations are analyzed. Monthly averages are determined after the rejection of the extreme values. The series are homogenized, based on linear regression between neighbor stations, by interpolation and by filling data gaps with seasonal means. To determine the linear trend a multiple linear regression model is used, including different impact factors as the solar activity, the aerosol loading, the El Nino impact. The QBO effect on the NO2 variation is also checked. With small exceptions the examined data show no significant trends. A significant solar activity impact on NO2 was determined only for the station at Mauna Loa. An influence of the south oscillation index was established for the Izaña station. The significances of the impacts are tested, taking into account the auto-correlation of the NO2 residuals. The density variations of the stratospheric NО2 can change the ozone concentration, which in turn influences the radiative balance in the stratosphere and troposphere. This makes the NO2 trend analysis important for the global climate change study.
Highlights ► NO2 time series of 4 mid-latitude stations and 2 subtropical ones are analyzed. ► The series are homogenized, based on linear regression. ► For determination of trends a multiple linear regression model is used. ► Not significant trends are found. ► A solar activity influences on NO2 was found only for the Mauna Loa station.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): H. Koshiishi , H. Matsumoto
The Technical Data Acquisition Equipment on board the Advanced Land Observing Satellite had been operated in low earth orbit at 700km altitude from 2006 through 2011 in order to evaluate space radiation environment, especially the proton environment and the electron environment in the radiation belts, during solar-activity minimum period. The activation of the electron environment in the inner radiation belt along with the 24th solar-activity cycle started in the beginning of 2010, 1 year after the beginning of the 24th solar-activity cycle itself in the end of 2008. The electron environment in the outer radiation belt was almost always modulated by solar wind variations; however, it showed very low activities in the beginning of 2010 which was the same time when the lowest activities were seen in the inner radiation belt. On the other hand, the proton environment in the inner radiation belt showed a slight increase as solar activity went lower, and had a peak also in the beginning of 2010, the same time when there was maximum galactic cosmic ray flux. 1-year delay of the response of space radiation environment around the Earth is suggested to be because the beginning of the 24th solar-activity cycle was very quiet as compared with the several former solar-activity cycles.
Highlights ► The space environment in low earth orbit from 2006 through 2011 had been measured. ► The activation of the electron environment started in the beginning of 2010. ► The activation started about 1 year after the beginning of solar-activity cycle itself.
Abstract: Publication date: July 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 99
Author(s): J. Manninen , N.G. Kleimenova , O.V. Kozyreva , P.A. Bespalov , A.E. Kozlovsky
Non-typical long lasting quasi-periodic (QP) VLF emissions have been recorded in Northern Finland at L∼5.3 during the recent Finnish VLF campaign held in December 2011. Contrary to the typical daytime QP emissions, the night-time and early morning (00–05UT) event reported here for the first time is a sequence of 1.5–3.5kHz noise bursts lasting for several tens of seconds with an unusually long repetition period which gradually decreases from ∼700s to ∼50s. These QP emissions were observed under conditions of very quiet geomagnetic activity (K p =0). In spite of that, the interplanetary magnetic field generally had a small southward component, and a high-latitude substorm occurred on the night-side. After this substorm, the repetition period of the VLF bursts suddenly dropped from ∼200s to∼60s and the spectral structure of QP wave changed. We attribute these QP emissions to auto-oscillations of the cyclotron instability of the Earth's radiation belts. According to the theory, the repetition period of the QP should be inversely proportional to the flux of the gyroresonant energetic electrons. Thus the increased flux of energetic electrons injected by the substorm probably led to the decreasing QP repetition periods.
Highlights ► Non-typical quasi-periodic (QP) VLF emissions have been recently found. ► These emissions were observed under conditions of quiet geomagnetic activity (K p =0). ► The night-time and early morning QP event was reported here for the first time. ► These were auto-oscillations of the cyclotron instability of the radiation belts.
Abstract: Publication date: June 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 98
Author(s): Shaohua Gong , Guotao Yang , Jiyao Xu , Jihong Wang , Sai Guan , Wei Gong , Jun Fu
Abstract: Publication date: August 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 100–101
Author(s): D.I. Vavilov , D.R. Shklyar , E.E. Titova , M. Parrot
Variations of plasma distribution and/or wave spectral features in the ionosphere were suggested by many authors as possible earthquake precursors, and the change of plasma density and temperature above seismic regions were reported in the literature. These quantities are known to influence the lower hybrid resonance (LHR) frequency profiles in the upper ionosphere and the magnetosphere, which, in turn, strongly affects the propagation of quasi-resonance VLF waves with frequencies f close to the maximum of the LHR frequency on the propagation path. This makes the VLF signals a tool of registration of ionospheric perturbations. Using the measurements from the DEMETER satellite for 3yr we have calculated the maps of LHR frequency over the globe, and the maps of VLF spectral intensity at the frequencies of Alpha navigation transmitters. These maps demonstrate a significant dependence of the spectral intensity in the transmitter conjugate region on the relation between the signal frequency and the LHR frequency above the observation point. Then, using the DEMETER data and the earthquake database from the US geological survey server we have performed statistical analysis of the LHR frequency over seismic regions and found an appreciably different behaviour of the LHR frequency before earthquakes, as compared to its regular behaviour, for several seismic regions. Although this difference is statistically significant, in each particular case the ionospheric perturbations may be related to different processes in the Earth's atmosphere, ionosphere, and the magnetosphere, other than gathering earthquakes. Thus, the unexpected variations in the LHR frequency profile, revealed from the variations of VLF transmitter signals, should only be considered as one indicator in a list of possible earthquake precursors.
Abstract: Publication date: June 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 98
Author(s): H. Takahashi , K. Shiokawa , F. Egito , Y. Murayama , S. Kawamura , C.M. Wrasse
Upper mesosphere airglow emissions and temperature observed at Rikubetsu (43.5°N,143.8°E) and mesospheric winds observed at Wakkanai (45.4°N,141.8°E), Japan, from January to December 2005 were used to analyze periodic oscillations of 2–16 days. During the January to March period and after September, both winds and airglow demonstrated clear 8-, 10- and 16-day oscillations. Downward phase progressions observed in the oscillations indicate that these are a signature of Rossby mode planetary waves. The 16-day wave was more evident in the zonal wind than the meridional. The 10-day wave was observed in January and March, on the basis of only a few cycles superposed on the 16-day wave. Airglow OI 557.7nm, O2 and OH(6,2) band emissions and O2 rotational temperature also showed significant amplitude of oscillation induced by the wave passages. For the 10-day wave, OI557.7nm showed an amplitude of oscillation equals to or more than 50% of the mean intensity level, O2 ∼45% and OH ∼25%. Large amplitudes of oscillation of the airglow during the passage of planetary waves suggest the possible vertical transport of atomic oxygen in addition to the density and temperature variations intrinsic to the wave events.
Abstract: Publication date: Available online 17 April 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Adarsh Kumar
In the present study, the Moderate Resolution Imaging Spectroradiometer (MODIS) data retrieved from Terra satellite has been used to investigate the spatial and temporal variations in aerosol particles over North Eastern region of India for the period (2001-10). Aerosol optical depths have found to be increased >15% across North Eastern part of India during the last decade (2001–2010). During the summer season, the mean AOD values (0.60±0.07) were observed whereas during the post monsoon season, mean AOD values were observed to be (0.07±0.02). Highest annual mean increase of AOD (> 79%) has been found over Guwahati. We then studied the relationship between AOD and five other cloud parameters namely water vapor, cloud fraction, cloud top temperature, cloud top pressure and cloud optical depth over North Eastern part of India so as to provide a better understanding of aerosol-cloud interaction.
Abstract: Publication date: June 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 98
During a period of heliospheric disturbance in 2007–9 associated with a co-rotating interaction region (CIR), a characteristic periodic variation becomes apparent in neutron monitor data. This variation is phase-locked to periodic heliospheric current sheet crossings. Phase-locked electrical variations are also seen in the terrestrial lower atmosphere in the southern UK, including an increase in the vertical conduction current density of fair weather atmospheric electricity during increases in galactic cosmic ray-induced neutron monitor count rate at the surface and energetic proton count rates measured by geosynchronous spacecraft. At the same time as the conduction current increases, changes in the cloud microphysical properties lead to an increase in the detected height of the cloud base at Lerwick Observatory, Shetland, with associated changes in surface meteorological quantities. As electrification is expected at the base of layer clouds, which can influence droplet properties, these observations of phase-locked thermodynamic, cloud, atmospheric electricity and solar sector changes are not inconsistent with a heliospheric disturbance driving lower troposphere changes.
Abstract: Publication date: June 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 98
This study presents the response of African equatorial GPS-TEC to intense geomagnetic storms that occurred during the ascending phase (2011–2012) of solar cycle 24. Specifically, four intense geomagnetic storms were considered: September 26–27, 2011 storm (Dst: −103nT), October 25, 2011 (Dst: −137nT), March 9, 2012 storm (Dst: −133nT), and July 15, 2012 storm (Dst: −126nT). Furthermore, the responses of GPS-TEC data from three African equatorial stations: Addis Ababa (9.04°N, 38.77°E, 0.18°N magnetic latitude) [Ethiopia]; Lagos (6.52°N, 3.4°E, 3.04°S magnetic latitude) [Nigeria]; and Malindi (3.00°S, 40.20°E, 10.98°S magnetic latitude) [Kenya] to the geomagnetic storms under investigation were also studied. We also examine the causative roles of interplanetary (IP) structures in the formation of the intense geomagnetic storms. All the intense storms were found to be associated with CME-induced transients, and their drivers were sheath fields behind the shocks. At the African equatorial zone, TEC exhibits positive response to intense geomagnetic storms, with enhancements in the order of 6–25 TECU around 1300–1500 UT.
Abstract: Publication date: Available online 8 April 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Saturation in the dependence of foF2 on solar flux is a phenomenon more pronounced in the equatorial ionization anomaly region. The phenomenon was observed in the relationship between the F2 critical frequency (foF2) and any solar indices. Using a two-segmented regression fit on data from an African low latitude station (Geographical Latitude 12.4°N; Geomagnetic Latitude 3.5°N), saturation features from the dependence of foF2 on solar radio flux (F10.7) was studied. Diurnal and seasonal variation were studied for the first time in this low latitude region of the African sector. Significant variations were observed, especially in the solstices. It was observed that saturation effect is closely related to the hourly F2 critical frequency and these results were compared with those from Asian, Australian and the American sectors. The diurnal and seasonal variations find their explanations in the photo-ionization process, the fountain effect, and the pre-reversal enhancement while the seasonal variation was attributed to both the ion drift and thermospheric circulation. Future work with larger volume of data is expected to validate the observations from this study.
Abstract: Publication date: June 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 98
An aerosol-type specific heterogeneous nucleation parameterization that based on the classical nucleation theory has been implemented into the atmospheric general circulation model (AGCM), ECHAM5. The microphysical responses in precipitation formation to the variation of ice nuclei (IN) species over Indian subcontinent were analyzed using AGCM, considering the immersion freezing nucleation from mineral dust, dust with ammonium sulfate coating, soot and bacteria species. Immersion freezing by bacteria species is found to be dominating in October–December, whereas dust with ammonium sulfate produces more cloud ice in January–March. There are very little differences in cloud ice formation during April–May and June–September among various IN species. There is also a geographic dependence in the role of different IN species in precipitation formation, like bacteria is important in Southern Peninsula and dust particles play a significant role in central India. In nature the emission of ice nucleating active bacteria and non-biological dust, soot into the atmosphere is important and highly dependent on temperature, and precipitation. So it is the worthy of investigation on the role of different kind of aerosols on the microphysics and precipitation processes, the biosphere–atmosphere interaction and climatic research.
Abstract: Publication date: June 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 98
The present study is an analysis of the effects of storm sudden commencements (SSC) on geomagnetic field components H, D and Z during 1995–2001 with the data of five low-latitude stations in India, namely Pondicherry (PND, 2.85°N, 79.92°E), Visakhapatnam (VSK, 8.34°N, 83.32°E), Alibag (ABG, 10.19°N, 72.87°E), Nagpur (NGP, 12.12°N, 79.08°E) and Ujjain (UJJ, 14.43°N, 75.78°E). The characteristics of geomagnetic H, D and Z field components are studied under various geophysical conditions. For both quiet and storm times, the maximum amplitude of H is obtained at PND and it decreases with increase in latitude for the period 1995–2001.The amplitude of D component is larger at VSK and smaller at UJJ for both quiet and storm periods during 1995–2001. It is clear that the storm time H min values show no variation with solar activity at 2.85°N (PND). However, all the other latitudes in the present study such as at 8.34°N, 10.19°N, 12.12°N and 14.43°N, storm time H min values decrease with increase of S10.7. The values of ΔH min shows positive correlations with solar activity, for the stations PND, VSK, ABG, NGP and UJJ, considered in the present study. The value of correlation coefficient obtained between H and interplanetary magnetic field and H and interplanetary electric field increases with increase of solar activity. The values of ΔH min (ΔH min=H storm−H quiet) increase with increase of solar activity and correlate well with Dst max for the five low-latitudes studied here.
Abstract: Available online 2 April 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
The Schumann resonances (SR) are of great significance for probing the global circuit. The diurnal and seasonal variations in mode amplitudes and frequencies of the first four modes of SR magnetic components based on two years measurements at the stations located in China are firstly presented here. The frequencies of all the four modes have their maxima during boreal winter and minima during summer, while the mode amplitudes change oppositely. The variations of both frequencies and amplitudes show their strong relationships with the lighting activity in south-east Asia (0800 UT) which is the nearest source to the observatories in China, while the other sources in Africa (1400 UT) and South America (2000 UT) have less effects on the mode amplitudes of both magnetic components. The effect of day-night asymmetry on SR parameters is estimated by a 3D-FDTD model of the Earth-ionosphere cavity with a single pulse traveling around the equator in a day. Two models of the Earth-ionosphere cavity, namely, a symmetric cavity and a cavity with day-night asymmetric conductivity profile are exploited. It is clear that the minima in the diurnal patterns of the mode frequencies near local sunrise/sunset times are mainly related to the migrations of the global lighting activity, not the day-night ionosphere asymmetry. Moreover, it is concluded that the ionosphere-induced variations of SR parameters including mode frequencies and amplitudes are much smaller than the variations resulting from lighting activity.
Abstract: Available online 3 April 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
A form of range-time plots derived from ionograms taken from a standard digital ionosondes, situated at the low latitude sites of Vanimo, Port Moresby and Darwin, exhibit bursts of spread F at the centre of descending and ascending off-angle reflectors. This particular type of event has since been identified with the passage of optically imaged ionospheric plasma depletions (bubbles) over a Darwin ionosonde. This paper describes the process for producing this form of range-time display and its relationship to ionospheric height, satellite traces and range spread F as seen on individual ionograms. First hop satellite traces are proposed to be via direct reflection from the steep electron density gradients at the base of bubbles while second hop satellite traces then involve a single additional ground reflection. Measurements of night equatorial drift velocity were made from the range-time displays and found to be in the range 20–220m/s peaking at approximately 90–100m/s in good agreement with values derived from drift measurements made by a variety of other types of equipment.
Abstract: Available online 3 April 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
This study examines the phase dependant temporal and spatial error evolution and prediction of active break spells of Indian Summer Monsoon rainfall in an Ensemble Prediction System (EPS) on a pentad time scale using Climate Forecast System (CFS). The EPS system shows systematic wet bias (overestimation) over west coast over the Arabian Sea and Myanmar coast and dry bias (underestimation) over Indian land mass even at pentad 1 lead and these biases consistently increase up to 4 pentad lead and saturate thereafter. Irrespective of the phases of the monsoon, the lower bound of predictability is 2 pentads, while upper bound of predictability for initial conditions starting from active phase saturates at 3 pentads and for break and transition phases predictability error saturates at a later stage at about 5 pentad. Initial conditions started from transition phase shows higher potential predictability followed by break phase and then active phase.
Abstract: Available online 21 March 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
The goal of this article is to investigate the influence of solar activity on thunderstorm activity in Brazil. For this purpose, thunder day data from seven cities in Brazil from 1951 to 2009 are analyzed with the wavelet method for the first time. To identify the 11-year solar cycle in thunder day data, a new quantity is defined. It is named TD1 and represents the power in 1-year in a wavelet spectrum of monthly thunder day data. The wavelet analysis of TD1 values shows more clear the 11-year periodicity than when it is applied directly to annual thunder day data, as it has been normally investigated in the literature. The use of this new quantity is shown to enhance the capability to identify the 11-year periodicity in thunderstorm data. Wavelet analysis of TD1 indicates that six out seven cities investigated exhibit periodicities near 11 years, three of them significant at a 1% significance level (p<0.01). Furthermore, wavelet coherence analysis demonstrated that the 11-year periodicity of TD1 and solar activity are correlated with an anti-phase behavior, three of them (the same cities with periodicities with 1% significance level) significant at a 5% significance level (p<0.05). The results are compared with those obtained from the same data set but using annual thunder day data. Finally, the results are compared with previous results obtained for other regions and a discussion about possible mechanisms to explain them is done. The existence of periodicities around 11 years in six out of seven cities and their anti-phase behavior with respect to 11-year solar cycle suggest a global mechanism probably related to a solar magnetic shielding effect acting on galactic cosmic rays as an explanation for the relationship of thunderstorm and solar activity, although more studies are necessary to clarify its physical origin.
Abstract: Available online 21 March 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Global Navigation Satellite System (GNSS) based radio occultation (RO) technique has shown powerful ability in ionospheric electron density profiling in the past decade. The most frequently used Abel inversion method in electron density retrieval has some biases because of the used spherical symmetry assumption. Our previous series simulations and evaluations mainly concentrated in the middle and low latitude regions have shown some systematical bias especially in lower altitude of low latitude region. However, the RO derived electron density quality in the high latitude and polar region is rarely investigated and not quantitatively clear yet. In this study, the Abel inversion error over high latitude and polar regions are systematically investigated for the first time based on NCAR-TIEGCM simulations and real data evaluations. The TIMED data driven NCAR-TIEGCM modeled electron density during 2008 are used to simulate the COSMIC RO events. The Abel inversion error can then be estimated by comparing Abel retrievals from TIEGCM simulated occultation with the original TIEGCM simulations. The Abel inversion can reproduce the season, altitude, latitude, and local time variation patterns of electron density and auroral zone electron density nighttime enhancement well in high latitude and polar region. The Abel inversion tends to underestimate the electron density in the auroral zone and overestimate it on both the equatorward and poleward sides of the auroral zone. As simulated by the TIEGCM model, the significant relative error (>25%) mainly occurs in lower altitude (<250km) inside and around auroral zone region. Above 250km, the relative error mostly is less than 25%. Specifically, RMSE (root mean square error) of NmF2 error from simulation is ∼8.5%. The Abel error under real ionosphere situation would be worse because the ionosphere could be more complicated and noisier than the model simulation. The error distribution and its seasonal, local time and latitude variations can be explained by the spherical symmetry assumption used in the Abel inversion associated with the corresponding ionospheric electron density variations. The comparisons between PFISR and COSMIC RO electron density during 2007–2011 and some previous validation studies agree well with our simulation results. We hope these results can stimulate more studies in high latitude ionospheric research using RO data.
Highlights ► We use TIMED driven TIEGCM results to simulate the COSMIC RO events during 2008. ► 2, Abel inversion error in high latitude and polar region is systematically estimated. ► 3, Abel inversion underestimates EDP in aurora zone and overestimates in both sides. ► 4, Above 250km, the relative error of EDP is less than 25%. RMSE of NmF2 error is ∼8.5%. ► Comparison between PFISR and COSMIC during 2007–2011 confirms the simulations.
Abstract: Available online 22 March 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Tropopause temperature ( T t ) and pressure ( p t ) at Nanjing are derived from the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) from August 2006 to December 2011. We compare T t and p t among the COSMIC, radiosonde provided by the Earth System Research Laboratory (ESRL) and reanalysis data sets from the National Centers for Environmental Prediction–National Center for Atmospheric Research (NCEP‐NCAR) Reanalysis (NNR) on ten-day, seasonal and annual timescales. Ten-day mean T t and p t of the COSMIC data are higher than that of radiosonde by 0.2°C and 5.3hPa and reanalysis by 1.0°C and 17.5hPa, respectively. Results of multiple comparisons demonstrate a significant difference for p t between the NNR and COSMIC data. Systematic biases are more significant in low-pressure level than in high-pressure level for reanalysis and radiosonde in terms of seasonal average differences. As for annual mean difference pressure, the COSMIC is higher than ESRL and NNR data by 3.4–6.5hPa and 10hPa, respectively. Besides, the COSMIC and other two data sets are in the best agreement for T t and p t with maximum number of occultation events in 2008. Lastly, quasi-biennial period of correlation coefficients between the ESRL and NNR data sets from 2007 to 2011 requests further verification.
Abstract: Available online 14 March 2013 Publication year: 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Simultaneous ten quiet days records of slant total electron content (STEC) and the horizontal magnetic field intensity (H-field) from each month of the year 2009 are employed for this work. The STEC and the H-field are measured from Global Positioning System (GPS) and the Magnetic Data Acquisition System (MAGDAS) respectively at Ilorin, Nigeria. The vertical total electron content (VTEC) and solar quiet of H-component (S q H) values are estimated from the STEC and H-field data respectively. Daily maximum value of S q H (DS q H) in October is 87nT and the minimum value in January is 18nT around 1000–1200 LT. With the exclusions of months with pre-noon peaks, maximum daily value of VTEC (DTEC) was observed at 1500 LT in October with a value of 34 TECU and with a minimum value of 24 TECU in February. During the pre-sunrise towards the sunrise period at the equatorial-trough, prominent westward electric field associated with increasing DS q H variations were due to probable late reversal of the westward nighttime to eastward daytime electric field, which plays significant role of generating equatorial ionization anomaly (EIA) at the equatorial-trough. The maximum peak time of DS q H closely determines the time of pre-noon peak on the DTEC variability when there is no prominent CEJ during the rising flank. On the decaying flanks, CEJ were observed to impede plasma deposition on DTEC variation. The estimates of correlation coefficient (cc) of DTEC and DS q H are also investigated. Seasonal variations investigated show that there exist a relationship between DTEC and DS q H, which is an evidence of EIA.
Highlights ► The equatorial ionization anomaly is characterized by plasma transportation. ► The vertical plasma drift was initiated by the equatorial electrojet. ► The equatorial electojet is peculiar to solar quiet.
PubDate: 2013-03-16T03:07:34Z
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