(Total: 82 journals)
- Equatorial spread-F occurrence observed at two near equatorial stations in
the Brazilian sector and its occurrence modulated by planetary waves
- Abstract: Publication date: March 2011
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 73, Issue 4
Author(s): F.C.P. Bertoni , Y. Sahai , J.-P. Raulin , P.R. Fagundes , V.G. Pillat , C.G. Gimenez de Castro , W.L.C. Lima
In this work, we present a study on the ionospheric Equatorial Spread-F (ESF) occurrence and morphologic features, based on measurements made during the period of October 2005 and January 2006 and May–July 2006 by digital ionosondes operating at two near magnetic equator locations, namely, Palmas (10.2°S, 48.2°W; dip lat. 5.5°S) and Manaus (3.1°S, 60.0°W; dip lat. 6.4°N), Brazil. The ionospheric height related parameter (h′F), the ionospheric density related parameter (foF2), and the dynamo-electric fields inferred from h′F time derivative (dh′F/dt) were analyzed with wavelets transform. The results exhibit periodic nature with wave-like signatures of 12–16 days. On the other hand, the electron density time variability (dNe/dt) was also analyzed using wavelets transform, and it presented planetary wave modulation with episodic nature. The ESF start time variability demonstrates to have a periodic signature of approximately 15 days with a good significance level, and it has a tendency to be anti-correlated with the pre-reversal enhancement time velocity (dh′F/dt), showing that larger vertical drift velocities (ionospheric uplift) may contribute to generate earlier ESF occurrence.
Highlights ►Ionospheric Equatorial Spread-F (ESF) occurrence and morphologic features are shown. ►Ionospheric parameters were analyzed with wavelets transform. ►Planetary wave type oscillation (PWTO) periodicities are seen in these parameters. ►Dynamo-electric field modulation by PWTO is proposed as a transport mechanism. ►ESF start time occurrence showed PWTO periodicities.
- Plasma modifications induced by an X-mode HF heater wave in the high
latitude F region of the ionosphere
- Abstract: Publication date: December 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 105–106
Author(s): N.F. Blagoveshchenskaya , T.D. Borisova , T.K. Yeoman , M.T. Rietveld , I. Häggström , I.M. Ivanova
We presented experimental results of strong plasma modifications induced by X-mode powerful HF radio waves injected towards the magnetic zenith into the high latitude F region of the ionosphere. The experiments were conducted in 2009–2011 using the EISCAT Heating facility, UHF incoherent scatter radar and the EISCAT ionosonde at Tromsø, Norway; and the CUTLASS SuperDARN HF coherent radar at Hankasalmi, Finland. The results showed that the X-mode HF pump wave can generate strong small-scale artificial field aligned irregularities (AFAIs) in the F region of the high-latitude ionosphere. These irregularities, with spatial scales across the geomagnetic field of the order of 9–15m, were excited when the heater frequency (f H) was above the ordinary-mode critical frequency (foF2) by 0.1–1.2MHz. It was found that the X-mode AFAIs appeared between 10s and 4min after the heater is turned on. Their decay time varied over a wide range between 3min and 30min. The excitation of X-mode AFAIs was accompanied by electron temperature (Te) enhancements and an increase in the electron density (Ne) depending on the effective radiated power (ERP). Under ERPs of about 75–180MW the Te enhances up to 50% above the background level and an increase in Ne of up to 30% were observed. Dramatic changes in the Te and Ne behavior occurred at effective radiated powers of about 370–840MW, when the Ne and Te values increased up to 100% above the background ones. It was found that AFAIs, Ne and Te enhancements occurred, when the extraordinary-mode critical frequency (fxF2) lied in the frequency range f H–f ce/2≤fxF2≤f H+f ce/2, where f ce is the electron gyrofrequency. The strong Ne enhancements were observed only in the magnetic field-aligned direction in a wide altitude range up to the upper limit of the UHF radar measurements. In addition, the maximum value of Ne is about 50km higher than the Te enhancement peak. Such electron density enhancements (artificial ducts) cannot be explained by temperature-dependent reaction rates. They can be attributed to HF-induced ionization production by accelerated electrons. The possible mechanisms for plasma modifications induced by powerful X-mode HF radio waves were discussed.
Highlights ► Strong plasma modification induced by high power X-mode HF radio waves. ► Excitation of artificial irregularities in the F region of the high-latitude ionosphere. ► Enhancements in the electron temperature and density under X-mode HF heating. ► Generation of artificial ducts of strongly enhanced electron density
- Bite-outs and other depletions of mesospheric electrons
- Abstract: Publication date: September 2011
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 73, Issues 14–15
Author(s): Martin Friedrich , Markus Rapp , John M.C. Plane , Klaus M. Torkar
The ionised mesosphere is less understood than other parts of the ionosphere because of the challenges of making appropriate measurements in this complex region. We use rocket borne in situ measurements of absolute electron density by the Faraday rotation technique and accompanying DC-probe measurements to study the effect of particles on the D-region charge balance. Several examples of electron bite-outs, their actual depth as well as simultaneous observations of positive ions are presented. For a better understanding of the various dependencies we use the ratio β/α i (attachment rate over ion–ion recombination coefficient), derived from the electron and ion density profiles by applying a simplified ion-chemical scheme, and correlate this term with solar zenith angle and moon brightness. The probable causes are different for day and night; recent in situ measurements support existing hypotheses for daytime cases, but also reveal behaviour at night hitherto not reported in the literature. Within the large range of β/α i values obtained from the analysis of 28 high latitude night flights one finds that the intensity of scattered sunlight after sunset, and even moonlight, apparently can photodetach electrons from meteoric smoke particles (MSP) and molecular anions. The large range of values itself can best be explained by the variability of the MSPs and by occasionally occurring atomic oxygen impacting on the negative ion chemistry in the night-time mesosphere under disturbed conditions.
Highlights ► Bite-outs: high-quality radio wave propagation data support the bite-out depth measured by plasma probes. ► Photodetachment: scattered sunlight and moonlight can influence detachment of electrons from molecules and MSP’s. ► Meteoric smoke particles: nocturnal electron loss is highly variable and best explained by the variability of MSP’s.
- The ionospheric outflow feedback loop
- Abstract: Publication date: August 2014
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 115–116
Author(s): T.E. Moore , M.-C. Fok , K. Garcia-Sage
Following a long period of observation and investigation beginning in the early 1970s, it has been firmly established that Earth׳s magnetosphere is defined as much by the geogenic plasma within it as by the geomagnetic field. This plasma is not confined to the ionosphere proper, defined as the region within a few density scale heights of the F-region plasma density peak. Rather, it fills the flux tubes on which it is created, and circulates throughout the magnetosphere in a pattern driven by solar wind plasma that becomes magnetically connected to the ionosphere by reconnection through the dayside magnetopause. Under certain solar wind conditions, plasma and field energy is stored in the magnetotail rather than being smoothly recirculated back to the dayside. Its release into the downstream solar wind is produced by magnetotail disconnection of stored plasma and fields both continuously and in the form of discrete plasmoids, with associated generation of energetic Earthward-moving bursty bulk flows and injection fronts. A new generation of global circulation models is showing us that outflowing ionospheric plasmas, especially O+, load the system in a different way than the resistive F-region load of currents dissipating energy in the plasma and atmospheric neutral gas. The extended ionospheric load is reactive to the primary dissipation, forming a time-delayed feedback loop within the system. That sets up or intensifies bursty transient behaviors that would be weaker or absent if the ionosphere did not “strike back” when stimulated. Understanding this response appears to be a necessary, if not sufficient, condition for us to gain accurate predictive capability for space weather. However, full predictive understanding of outflow and incorporation into global simulations requires a clear observational and theoretical identification of the causal mechanisms of the outflows. This remains elusive and requires a dedicated mission effort.
- The long sunspot cycle 23 predicts a significant temperature decrease in
- Abstract: Publication date: May 2012
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 80
Author(s): Jan-Erik Solheim , Kjell Stordahl , Ole Humlum
Relations between the length of a sunspot cycle and the average temperature in the same and the next cycle are calculated for a number of meteorological stations in Norway and in the North Atlantic region. No significant trend is found between the length of a cycle and the average temperature in the same cycle, but a significant negative trend is found between the length of a cycle and the temperature in the next cycle. This provides a tool to predict an average temperature decrease of at least 1.0 ° C from solar cycle 23 to solar cycle 24 for the stations and areas analyzed. We find for the Norwegian local stations investigated that 25–56% of the temperature increase the last 150 years may be attributed to the Sun. For 3 North Atlantic stations we get 63–72% solar contribution. This points to the Atlantic currents as reinforcing a solar signal.
Highlights ► A longer solar cycle predicts lower temperatures during the next cycle. ► A 1°C or more temperature drop is predicted 2009–2020 for certain locations. ► Solar activity may have contributed 40% or more to the last century temperature increase. ► A lag of 11 years gives maximum correlation between solar cycle length and temperature.
- Intensity of climate variability derived from the satellite and MERRA
reanalysis temperatures: AO, ENSO, and QBO
- Abstract: Publication date: April 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volumes 95–96
Author(s): Jung-Moon Yoo , Young-In Won , Myeong-Jae Jeong , Kyu-Myong Kim , Dong-Bin Shin , Yu-Ri Lee , Young-Jun Cho
Satellite measurements (Atmospheric InfraRed Sounder/Advanced Microwave Sounding Unit-A, MODerate resolution Imaging Spectroradiometer) and the Modern Era Retrospective-analysis for Research and Applications (MERRA) reanalysis have been utilized to analyze the relative influence of the climate variability (AO: Arctic Oscillation, ENSO: El Niño-Southern Oscillation, QBO: Quasi-Biennial Oscillation) on the zonal-mean temperature and wind variations over the globe from September 2002 to August 2011. We also extended the usage of MERRA data for the period of 1979–2011; furthermore, three climate indices of AO, NINO3.4, and QBO were used as the corresponding climate indicators. The correlations between the temperature anomalies and the climate indices indicate that the tropospheric temperature variability in the mid-latitude (30–60N) linked to both AO and ENSO has been more pronounced over ocean than over land. However, the low stratospheric temperature variability in the mid-latitude is mainly associated with ENSO and QBO. The north–south symmetric patterns over the globe are seen in the wind anomaly distributions for ENSO and QBO, but not for AO. The ENSO events are globally vigorous but also localized during the recent 9 years compared with those based on the period of 1979–2011. The tropospheric warming and stratospheric cooling phenomena during this period are more remarkable in the recent 9 years, although according to IPCC (2012). their linkage to the ENSO variability is still uncertain. The ENSO is found to have more significant impact on the tropospheric and low stratosphere temperature variability over the tropics in the recent period, consistent with more active zonal wind meridional circulations. The discrepancies between satellite observations and MERRA are also discussed. The estimated relative impact of the three major concurrent large-scale climate phenomena on regional temperature variability can be of great use in its long-term predictability.
Highlights ► Relative influence of AO, ENSO and QBO derived from satellite and MERRA temperatures. ► Tropospheric temperature in mid-latitude is linked to primarily AO and next to ENSO. ► Low stratospheric temperature in mid-latitude is mainly associated with ENSO and QBO. ► Tropospheric warming and stratospheric cooling are more remarkable in recent decade. ► More vigorous and localized ENSO events in recent decade, consistent with zonal wind.
- Multiscale studies of the three-dimensional dayside X-line
- 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.
- A reassessment of SuperDARN meteor echoes from the upper mesosphere and
- Abstract: Publication date: September 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 102
Author(s): Gareth Chisham , Mervyn P. Freeman
The Super Dual Auroral Radar Network (SuperDARN) is a network of HF radars used to study phenomena in the Earth's magnetosphere, ionosphere, and upper atmosphere. Phenomena in the upper mesosphere and lower thermosphere (MLT) can be studied as the SuperDARN radars act effectively as meteor radars at near ranges. However, SuperDARN meteor echo measurements from all heights have typically been combined together to give a height-averaged picture of large-scale characteristics and dynamics of the MLT. This is in part due to the uncertainty in the measurement of individual meteor echo heights, which is in turn partly due to the lack of reliable (and for some radars, the lack of any) interferometric information. Here, we present a method for calibrating SuperDARN interferometer data which reduces the systematic offsets in meteor echo height estimations. Using 9 years of SuperDARN data we then determine occurrence distributions of SuperDARN meteor echo heights. The distributions are approximately Gaussian with height, extending from ∼ 75 to ∼ 125 km and peaking around ∼ 102 – 103 km . In addition, we investigate whether the Doppler spectral width measured by the SuperDARN radars, which is related to the ambipolar diffusion coefficient for meteor echoes, can be used as a proxy measurement for meteor echo height. Due to the large spread of spectral width measurements at any one height we conclude that this proxy measurement is not practical and that the height of individual SuperDARN meteor echoes cannot be estimated without interferometric information. We also discuss how more accurate height information could be used to study the height variation of neutral wind velocities and the ambipolar diffusion coefficient across the MLT altitude range, and conclude that SuperDARN meteor echo observations have the potential to complement, and significantly extend the altitude range of, meteor echo observations from standard VHF meteor radars.
- Global propagation of gravity waves generated with the whole atmosphere
transfer function model
- Abstract: Publication date: November 2013
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 104
Author(s): Hans G. Mayr , Elsayed R. Talaat , Brian C. Wolven
A brief review is presented of the Transfer Function Model (TFM) [e.g., Mayr et al., Space Science Reviews, 1990], which describes acoustic gravity waves (AGW) that propagate across the globe in a dissipative and static (no winds) background atmosphere with globally uniform temperature and density variations extending from the ground to 700km. Unique among existing models, the TFM can be placed between the analytical approach on one end, and the rigorous numerical approach of general circulation models (GCM). The time consuming numerical integration of the conservation equations is restricted to compute the transfer function (TF) for a broad range of frequencies and spherical harmonics. Given TF, the atmospheric response for a chosen source configuration is then obtained in short order. Computationally efficient, the model is well suited to serve as experimental and educational tool for simulating propagating wave patterns across the globe. By design, the TFM is also semi-analytical and therefore well suited to explore the different wave modes that can be generated under different dynamical conditions.
- Vertical profile measurements of lower troposphere ionisation
- Abstract: Publication date: November 2014
Source:Journal of Atmospheric and Solar-Terrestrial Physics, Volume 119
Author(s): R.G. Harrison , K.A. Nicoll , K.L. Aplin
Vertical soundings of the atmospheric ion production rate have been obtained from Geiger counters integrated with conventional meteorological radiosondes. In launches made from Reading (UK) during 2013–2014, the Regener–Pfotzer ionisation maximum was at an altitude equivalent to a pressure of (63.1±2.4)hPa, or, expressed in terms of the local air density, (0.101±0.005)kgm−3. The measured ionisation profiles have been evaluated against the Usoskin–Kovaltsov model and, separately, surface neutron monitor data from Oulu. Model ionisation rates agree well with the observed cosmic ray ionisation below 20km altitude. Above 10km, the measured ionisation rates also correlate well with simultaneous neutron monitor data, although, consistently with previous work, measured variability at the ionisation maximum is greater than that found by the neutron monitor. However, in the lower atmosphere (below 5km altitude), agreement between the measurements and simultaneous neutron monitor data is poor. For studies of transient lower atmosphere phenomena associated with cosmic ray ionisation, this indicates the need for in situ ionisation measurements and improved lower atmosphere parameterisations.
- Mesospheric temperatures and sodium properties measured with the ALOMAR Na
lidar compared with WACCM
- Abstract: Publication date: Available online 16 January 2015
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Tim Dunker , Ulf-Peter Hoppe , Wuhu Feng , John M.C. Plane , Daniel R. Marsh
We present a comparison of the temperature and sodium layer properties observed by the ALOMAR Na lidar (69.3°N, 16.0°E) and simulated by the Whole Atmosphere Community Climate Model with specified dynamics and implemented sodium chemistry (WACCM-Na). To constrain the meteorological fields below 60km, we use MERRA and GEOS-5. For the years 2008 to 2012, we analyze daily averages of temperature between 80.5km and 101.5km altitude, and of the Na layer's peak height, peak density, and centroid height. Both model runs are able to reproduce the pronounced seasonal cycle of Na number density and temperature at high latitudes very well. Especially between 86.5km and 95.5km, the measured and simulated temperatures agree very well. The lidar measurements confirm the model predictions that the January 2012 stratospheric warming led to large variation in temperature and Na density. The correlation coefficient between Na number density and temperature is positive for almost all altitudes in the lidar data, but not in the simulations. On average, the centroid height and peak height measured by lidar is about 2km to 3km higher than simulated by WACCM-Na.
- The crystal structure of ice under mesospheric conditions
- Abstract: Publication date: Available online 10 December 2014
Source:Journal of Atmospheric and Solar-Terrestrial Physics
Author(s): Benjamin J. Murray , Tamsin L. Malkin , Christoph G. Salzmann
Ice clouds form in the summer high latitude mesopause region, which is the coldest part of the Earth's atmosphere. At these very low temperatures (<150K) ice can exist in metastable forms, but the nature of these ices remains poorly understood. In this paper we show that ice which is grown at mesospherically relevant temperatures does not have a structure corresponding to the well-known hexagonal form or the metastable cubic form. Instead, the ice which forms under mesospheric conditions is a material in which cubic and hexagonal sequences of ice are randomly arranged to produce stacking disordered ice (ice I sd). The structure of this ice is in the trigonal crystal system, rather than the cubic or hexagonal systems, and is expected to produce crystals with aspect ratios consistent with lidar observations.