bluuebunny/crossref_metadata_2025 huggingface dataset:
The ionospheric responses to the 11 August 1999 solar eclipse: observations and modeling
Authors: Le H. , Liu L. , Yue X. , Wan W.
Published: June 2010

Abstract. A total eclipse occurred on 11 August 1999 with its path of totality passing over central Europe in the latitude range 40°–50° N. The ionospheric responses to this eclipse were measured by a wide ionosonde network. On the basis of the measurements of foE, foF1, and foF2 at sixteen ionosonde stations in Europe, we statistically analyze the variations of these parameters with a function of eclipse magnitude. To model the eclipse effects more accurately, a revised eclipse factor, FR, is constructed to describe the variations of solar radiation during the solar eclipse. Then we simulate the effect of this eclipse on the ionosphere with a mid- and low-latitude ionosphere theoretical model by using the revised eclipse factor during this eclipse. Simulations are highly consistent with the observations for the response in the E-region and F1-region. Both of them show that the maximum response of the mid-latitude ionosphere to the eclipse is found in the F1-region. Except the obvious ionospheric response at low altitudes below 500 km, calculations show that there is also a small response at high altitudes up to about 2000 km. In addition, calculations show that when the eclipse takes place in the Northern Hemisphere, a small ionospheric disturbance also appeared in the conjugate hemisphere.
The study of intermolecular energy transfers in electronic energy quenching for molecular collisions N2-N2, N2-O2, O2-O2
Authors: Kirillov A. S.
Published: June 2010

Abstract. Contributions of intermolecular electron energy transfers in the electronic quenching are calculated for molecular collisions N2(A3Σu+, W3Δu)+N2(X1Σg+, v=0), N2(A3Σu+)+N2(X1Σg+, v≥0), N2(A3Σu+)+O2(X3Σg−, v=0–2), O2(a1Δg, b1Σg+)+O2(X3Σg−, v=0–2). The calculation has allowed one to estimate the product branching ratios. It is shown that there is a dependence of the calculated rate coefficients on the vibrational excitation of N2(X1Σg+) and O2(X3Σg−) molecules. In many cases, the calculated rate coefficients have a good agreement with available experimental data.
Longitude-dependent decadal ozone changes and ozone trends in boreal winter months during 1960–2000
Authors: Peters D. H. W. , Gabriel A. , Entzian G.
Published: June 2010

Abstract. This study examines the longitude-dependent decadal changes and trends of ozone for the boreal winter months during the period of 1960–2000. These changes are caused primarily by changes in the planetary wave structure in the upper troposphere and lower stratosphere. The decadal changes and trends over 4 decades of geopotential perturbations, defined as a deviation from the zonal mean, are estimated by linear regression with time. The decadal changes in longitude-dependent ozone were calculated with a simple transport model of ozone based on the known planetary wave structure changes and prescribed zonal mean ozone gradients. For December of the 1960s and 1980s a statistically significant Rossby wave track appeared over the North Atlantic and Europe with an anticyclonic disturbance over the Eastern North Atlantic and Western Europe, flanked by cyclonic disturbances. In the 1970s and 1990s statistically significant cyclonic disturbances appeared over the Eastern North Atlantic and Europe, surrounded by anticyclonic anomalies over Northern Africa, Central Asia and Greenland. Similar patterns have been found for January. The Rossby wave track over the North Atlantic and Europe is stronger in the 1980s than in the 1960s. For February, the variability of the regression patterns is higher. For January we found a strong alteration in the modelled decadal changes in total ozone over Central and Northern Europe, showing a decrease of about 15 DU in the 1960s and 1980s and an increase of about 10 DU in the 1970s and 1990s. Over Central Europe the positive geopotential height trend (increase of 2.3 m/yr) over 40 years is of the same order (about 100 m) as the increase in the 1980s alone. This is important to recognize because it implies a total ozone decrease over Europe of the order of 14 DU for the 1960–2000 period, for January, if we use the standard change regression relation that about a 10-m geopotential height increase at 300 hPa is related to about a 1.4-DU total ozone decrease.
On the observed changes in upper stratospheric and mesospheric temperatures from UARS HALOE
Authors: Remsberg E.
Published: June 2010

Abstract. Temperature versus pressure or T(p) time series from the Halogen Occultation Experiment (HALOE) of the Upper Atmosphere Research Satellite (UARS) have been extended and re-analyzed for the period of 1991–2005 and for the upper stratosphere and mesosphere in 10-degree wide latitude zones from 60 S to 60 N. Even though sampling from a solar occultation experiment is somewhat limited, it is shown to be quite adequate for developing both the seasonal and longer-term variations in T(p). Multiple linear regression (MLR) techniques were used in the re-analyses for the seasonal and the significant interannual, solar cycle (SC-like or decadal-scale), and linear trend terms. Plots of the amplitudes and phases for the interannual (QBO and subbiennial) terms are provided. A simple SC-like term of 11-yr period was fitted to the time series residuals after accounting for the seasonal and interannual terms. Highly significant SC-like responses were found for both the upper mesosphere and the upper stratosphere. The phases of these SC-like terms were checked for their continuity with latitude and pressure-altitude; the larger amplitude responses are directly in-phase with that of standard proxies for the solar flux variations. The analyzed, max minus min, responses at low latitudes are of order 0.5 to 1 K, while at middle latitudes they are as large as 3 K in the upper mesosphere. Highly significant, linear cooling trends were found at middle latitudes of the middle to upper mesosphere (−1.5 to −2.0 K/decade), at tropical latitudes of the lower mesosphere (about −0.5 K/decade), and at 2 hPa (of order −1 K/decade). Both the diagnosed solar cycle responses and trends from HALOE for the mid to upper mesosphere at middle latitudes are larger than simulated with most models, perhaps an indication of decadal-scale dynamical forcings that are not being simulated so well.
Comparing Jupiter and Saturn: dimensionless input rates from plasma sources within the magnetosphere
Authors: Vasyliūnas V. M.
Published: June 2010

Abstract. The quantitative significance for a planetary magnetosphere of plasma sources associated with a moon of the planet can be assessed only by expressing the plasma mass input rate in dimensionless form, as the ratio of the actual mass input to some reference value. Traditionally, the solar wind mass flux through an area equal to the cross-section of the magnetosphere has been used. Here I identify another reference value of mass input, independent of the solar wind and constructed from planetary parameters alone, which can be shown to represent a mass input sufficiently large to prevent corotation already at the source location. The source rate from Enceladus at Saturn has been reported to be an order of magnitude smaller (in absolute numbers) than that from Io at Jupiter. Both reference values, however, are also smaller at Saturn than at Jupiter, by factors ~40 to 60; expressed in dimensionless form, the estimated mass input from Enceladus may be larger than that from Io by factors ~4 to 6. The magnetosphere of Saturn may thus, despite a lower mass input in kg s−1, intrinsically be more heavily mass-loaded than the magnetosphere of Jupiter.
Statistical study of inverted-V structures in FAST data
Authors: Partamies N. , Donovan E. , Knudsen D.
Published: June 2010

Abstract. Since the 1970s the inverted-V structures have been observed in the satellite-borne particle data. These Λ-shaped enhancements of the differential energy flux on the high energy channels on the top of low number flux on the lower energies are traces of auroral particle acceleration by U-shaped potential drops along the field lines within the auroral zones. In this study, we show the results of a statistical study of inverted-V events in five years (1997–2001) of the Fast Auroral SnapshoT (FAST) electron spectrograms. We found 588 well-defined events in total, but the statistical results are also shown for a subset of 97 very best events. The statistical analysis shows that the inverted-V's mainly occur within the auroral oval latitudes (65°–75° invariant latitude), in the pre-midnight sector (21–23 magnetic local time) and during the Northern Hemisphere winter months (November to February). The typical maximum energies of the inverted-V's are 2–4 keV, when a threshold value of 0.3 keV is used as a selection criterion. This corresponds to an acceleration potential drop of a few kV. The typical peak energy tends to increase towards the magnetic midnight. Most of the inverted-V events occur during magnetically quiet or moderate activity, Kp 1–4. The usual width of an inverted-V varies from 20 to 40 km and is comparable to the peak value of the typical meso-scale auroral arc width of 10–20 km. Furthermore, the polar cap potential values estimated from the SuperDARN radar data are always at least three times larger than the inverted-V acceleration potential drop.
Higher harmonic tweek sferics observed at low latitude: estimation of VLF reflection heights and tweek propagation distance
Authors: Kumar S. , Kishore A. , Ramachandran V.
Published: June 2010

Abstract. Lightning generated signals recorded at a low-latitude station, Suva (18.2° S, 178.3° E) Fiji, in the South Pacific region, during September 2003–July 2004, are used to study the propagation features and the reflection heights of tweek atmospherics in the waveguide formed by the Earth's surface and the lower ionosphere. Tweeks are observed only during the local night and the maximum harmonic (n) recorded is six. The occurrence of tweeks with higher n progressively decreases as n increases. The dispersed part of tweeks decreases as n increases. The attenuation factor has been calculated for tweeks with n=1–3. The ionospheric reflection heights obtained assuming the transverse magnetic mode of propagation for tweek signals vary from 83–92 km. A higher harmonic of the same tweek is reflected from about 2.0 km higher than the lower harmonic. For 90% of tweeks, propagation distances are estimated to be between 1000–5000 km. Tweeks with lower n propagate longer distances than the tweeks with higher n.
Bifurcation of the tail current sheet and ion temperature anisotropy
Authors: Israelevich P. L. , Ershkovich A. I.
Published: June 2010

Abstract. We investigated the relation between the geotail current sheet structure and the anisotropy of the ion temperature in the plasma sheet. Current density distribution in the geomagnetic tail is shown not to depend on the ratio between the parallel and perpendicular ion temperature. The tail current sheet bifurcation is controlled by non-gyrotropicity of plasma pressure: double peaked current density distribution is observed when the ion perpendicular temperature exhibits anisotropy, and the electric current density is stronger for larger ratio · (T⊥max−T⊥min)/T⊥. The current sheet thinning is accompanied by the perpendicular temperature anisotropy, and, generally, double-peaked current sheets are thinner than single-peaked sheets.
Evidence for particle acceleration in the magnetospheric cusp
Authors: Chen J.
Published: June 2010

Abstract. New evidence reveals that the charged particles can be energized locally in the magnetospheric cusp. The power spectral density of the cusp magnetic fluctuations shows increases by up to four orders of magnitude in comparison to an adjacent region. Large fluctuations of the cusp electric fields have been observed with an amplitude of up to 350 mV/m. The measured left-hand polarization of the cusp electric field at ion gyro-frequencies indicates that the cyclotron resonant acceleration mechanism is working in this region. The cyclotron resonant acceleration can energize ions from keV to MeV in seconds.
Multi-instrumentation observations of a transpolar arc in the northern hemisphere
Authors: Goudarzi A. , Lester M. , Milan S. E. , Frey H. U.
Published: June 2010

Abstract. A transpolar arc was imaged by the FUV instrument on the IMAGE spacecraft during a 3-h interval on 5 February 2002. Observations indicate that a burst of reconnection in the geomagnetic tail, which was not associated with a substorm, was responsible for the formation of the arc. The arc initially formed across the central polar cap, extending from near midnight to noon such that the polar cap was approximately divided in half. The subsequent motion of the arc was controlled by the amount of open flux being added to the dawn sector cap from a magnetopause reconnection site on the post-noon side of the magnetosphere. The dayside reconnection happened during a period when the IMF By component was dominant, although the Bz component initially remained positive, and resulted in strong westward azimuthal flows in the noon sector. The arc continued to move towards the duskside auroral oval after the IMF Bz turned southward. A keogram of the FUV/WIC auroral observations along the dawn-dusk meridian provides further evidence of the expansion and contraction of the polar cap during the period in which different IMF orientations occurred. Furthermore, comparing images from IMAGE and ionospheric convection flow from SuperDARN measurements, vortical convection flows occurred exactly at the time and location of the formation of the transpolar arc and subsequently followed the head of the transpolar arc as it moved across the polar cap. The observations are consistent with the prediction of a recent model for the formation of the transpolar cap by the closure of open flux in the geomagnetic tail, and its subsequent motion through changes in the open flux distribution within the polar cap.
The role of the vertical E×B drift for the formation of the longitudinal plasma density structure in the low-latitude F region
Authors: Oh S.-J. , Kil H. , Kim W.-T. , Paxton L. J. , Kim Y. H.
Published: June 2010

Abstract. The formation of a longitudinally periodic plasma density structure in the low-latitude F region by the effect of vertical E×B drift was investigated by analyzing the ROCSAT-1 satellite data and conducting SAMI2 model simulations. The daytime equatorial ionosphere observed during the equinox in 1999–2002 from ROCSAT-1 showed the formation of wave number-4 structures in the plasma density and vertical plasma drift. The coincidence of the longitudes of the peak density with the longitudes of the peak upward drift velocity during the daytime supported the association of the longitudinal density structure with the vertical E×B drift. The reproduction capability of the observed wave-4 structure by the effect of vertical E×B drift was tested by conducting SAMI2 model simulations during the equinox under solar maximum condition. When the ROCSAT-1 vertical drift data were used, the SAMI2 model could reproduce the observed wave-4 density structure in the low-latitude F region. On the other hand, the SAMI2 model could not reproduce the observed wave-4 structure using the Scherliess and Fejer vertical E×B drift model. The observation and model simulation results demonstrated that the formation of the longitudinally periodic plasma density structure can be explained by the longitudinal variation of the daytime vertical E×B drift.
Wind observations of low energy particles within a solar wind reconnection region
Authors: Huttunen K. E. J. , Bale S. D. , Salem C.
Published: June 2010

Abstract. We report characteristics of thermal particle observations during the encounter of the Wind satellite with the separatrix and the outflow domains of a reconnection event on 22 July 1999 in the solar wind. During the studied event the electrostatic analyzers on Wind were transmitting three-dimensional electron and proton distributions in a burst mode every 3 s, the spin period of the spacecraft. The event was associated with a magnetic shear angle of 114° and a large guide magnetic field. The observations suggest that Wind crossed the separatrix and outflow regions about a thousand of ion skin depths from the X-line. At the leading separator boundary, a strong proton beam was identified that originated from the direction of the X-line. In the separatrix and the outflow regions, the phase space distributions of thermal electrons displayed field aligned bidirectional anisotropy. During the crossings of the current sheets bounding the outflow region, we identified two adjacent layers in which the dominant thermal electron flows were towards the X-line at the inner edges of the current sheets and away from the X-line at the outer edges. Interestingly, simulation studies and observations in the Earth's magnetosphere have revealed that the electron flows are reversed, consistent with the Hall current system.
Seasonal and interannual variations of gravity wave activity in the low-latitude mesosphere and lower thermosphere over Tirunelveli (8.7° N, 77.8° E)
Authors: Sridharan S. , Sathishkumar S.
Published: June 2010

Abstract. The Mesosphere and Lower Thermosphere (MLT) winds acquired by medium frequency (MF) radar at Tirunelveli (8.7° N, 77.8° E) for the years 1993–2007 are used to study seasonal and interannual variabilities of gravity wave (GW) variances in the altitude region 84–94 km. The GW variances in zonal and meridional winds show semiannual oscillation with maximum variance during March–April and August–September and minimum during June–July and November–December months. The wind variances, in general, are observed to be enhanced during and after the year 1998 and they undergo large interannual variability, in particular, during spring equinox months. An enhancement of GW variances is observed during spring equinox months of the years 2000, 2004 and 2006. These larger GW enhancements, most of the times, coincide with eastward phase of zonally averaged stratospheric QBO at 30 hPa over equator and sudden stratospheric warming occurred at high latitudes. From the zonal and meridional variances, the perturbation ellipses are calculated and they show that the predominant direction of propagation of gravity waves is in SE-NW plane.
Gravity wave and tidal influences on equatorial spread F based on observations during the Spread F Experiment (SpreadFEx)
Authors: Fritts D. C. , Vadas S. L. , Riggin D. M. , Abdu M. A. , Batista I. S. , Takahashi H. , Medeiros A. , Kamalabadi F. , Liu H.-L. , Fejer B. G. , Taylor M. J.
Published: June 2010

Abstract. The Spread F Experiment, or SpreadFEx, was performed from September to November 2005 to define the potential role of neutral atmosphere dynamics, primarily gravity waves propagating upward from the lower atmosphere, in seeding equatorial spread F (ESF) and plasma bubbles extending to higher altitudes. A description of the SpreadFEx campaign motivations, goals, instrumentation, and structure, and an overview of the results presented in this special issue, are provided by Fritts et al. (2008a). The various analyses of neutral atmosphere and ionosphere dynamics and structure described in this special issue provide enticing evidence of gravity waves arising from deep convection in plasma bubble seeding at the bottomside F layer. Our purpose here is to employ these results to estimate gravity wave characteristics at the bottomside F layer, and to assess their possible contributions to optimal seeding conditions for ESF and plasma instability growth rates. We also assess expected tidal influences on the environment in which plasma bubble seeding occurs, given their apparent large wind and temperature amplitudes at these altitudes. We conclude 1) that gravity waves can achieve large amplitudes at the bottomside F layer, 2) that tidal winds likely control the orientations of the gravity waves that attain the highest altitudes and have the greatest effects, 3) that the favored gravity wave orientations enhance most or all of the parameters influencing plasma instability growth rates, and 4) that gravity wave and tidal structures acting together have an even greater potential impact on plasma instability growth rates and plasma bubble seeding.
Observations of vortex-like structure in the cusp-magnetosheath region during northward IMF orientation
Authors: Tkachenko O. , Šafránková J. , Němeček Z. , Šimůnek J. , Přech L.
Published: June 2010

Abstract. Two-point observations made by the Interball spacecraft pair unveiled a presence of a large vortex-like structure filled by slow and heated plasma in the outer cusp during periods of the positive BZ interplanetary magnetic field (IMF) component. We have observed the rotation of the magnetic field and the decrease of its magnitude connected with the presence of a hot plasma population inside the vortex. The structure starts with a clear reversal of the plasma flow caused by reconnection tailward of the cusp that turns a part of the magnetosheath plasma into the cusp. We compare the observations of two spacecraft in detail, discuss the differences between them and suggest the way of a formation such structure. Moreover, the statistical results have confirmed that this phenomenon is probably a regular feature of the high-altitude cusp, however, this relatively small structure cannot be observed too often. The alternative explanation of presented observations as a flapping of the magnetopause is taken into account and discussed.
Reconstruction of time-varying reconnection rate and X-line location
Authors: Ivanova V. V. , Semenov V. S. , Ivanov I. B. , Biernat H. K. , Kiehas S. A.
Published: June 2010

Abstract. Remote-sensing method developed on the basis of time-dependent Petschek-type reconnection model is applied to Cluster magnetotail measurements from 8 September 2002, where a series of earthward propagating NFTEs (nightside flux transfer events) was observed. The method utilizes single-spacecraft magnetic data as an input and provides the reconnection rate and the location of X-line as an output. For the first time the method is applied to a composite reconnection event consisting of three successive NFTEs following each other without any time delay. The reconnection distance is found to be between 27 and 30 RE in the tail. The reconstructed electric field involves three 1-min scale pulses with total duration of ~4 min. The peak rates for individual pulses vary from 0.6 to 1.1 mV/m.
Balanced reconnection intervals: four case studies
Authors: DeJong A. D. , Ridley A. J. , Clauer C. R.
Published: June 2010

Abstract. During steady magnetospheric convection (SMC) events the magnetosphere is active, yet there are no data signatures of a large scale reconfiguration, such as a substorm. While this definition has been used for years it fails to elucidate the true physics that is occurring within the magnetosphere, which is that the dayside merging rate and the nightside reconnection rate balance. Thus, it is suggested that these events be renamed Balanced Reconnection Intervals (BRIs). This paper investigates four diverse BRI events that support the idea that new name for these events is needed. The 3–4 February 1998 event falls well into the classic definition of an SMC set forth by Sergeev et al. (1996), while the other challenge some previous notions about SMCs. The 15 February 1998 event fails to end with a substorm expansion and concludes as the magnetospheric activity slowly quiets. The third event, 22–23 December 2000, begins with a slow build up of magnetospheric activity, thus there is no initiating substorm expansion. The last event, 17 February 1998, is more active (larger AE, AL and cross polar cap potential) than previously studied SMCs. It also has more small scale activity than the other events studied here.
A fuzzy neural network model to forecast the percent cloud coverage and cloud top temperature maps
Authors: Tulunay Y. , Şenalp E. T. , Öz Ş. , Dorman L. I. , Tulunay E. , Menteş S. S. , Akcan M. E.
Published: June 2010

Abstract. Atmospheric processes are highly nonlinear. A small group at the METU in Ankara has been working on a fuzzy data driven generic model of nonlinear processes. The model developed is called the Middle East Technical University Fuzzy Neural Network Model (METU-FNN-M). The METU-FNN-M consists of a Fuzzy Inference System (METU-FIS), a data driven Neural Network module (METU-FNN) of one hidden layer and several neurons, and a mapping module, which employs the Bezier Surface Mapping technique. In this paper, the percent cloud coverage (%CC) and cloud top temperatures (CTT) are forecast one month ahead of time at 96 grid locations. The probable influence of cosmic rays and sunspot numbers on cloudiness is considered by using the METU-FNN-M.
Escape of high-energy oxygen ions through magnetopause reconnection under northward IMF
Authors: Kasahara S. , Hasegawa H. , Keika K. , Miyashita Y. , Nishino M. N. , Sotirelis T. , Saito Y. , Mukai T.
Published: June 2010

Abstract. During a storm recovery phase on 15 May 2005, the Geotail spacecraft repeatedly observed high-energy (>180 keV) oxygen ions in the dayside magnetosheath near the equatorial plane. We focused on the time period from 11:20 UT to 13:00 UT, when Geotail observed the oxygen ions and the interplanetary magnetic field (IMF) was constantly northward. The magnetic reconnection occurrence northward and duskward of Geotail is indicated by the Walén analysis and convective flows in the magnetopause boundary layer. Anisotropic pitch angle distributions of ions suggest that high-energy oxygen ions escaped from the northward of Geotail along the reconnected magnetic field lines. From the low-energy particle precipitation in the polar cap observed by DMSP, which is consistent with magnetic reconnection occurring between the magnetosheath field lines and the magnetospheric closed field lines, we conclude that these oxygen ions are of ring current origin. Our results thus suggest a new escape route of oxygen ions during northward IMF. In the present event, this escape mechanism is more dominant than the leakage via the finite Larmor radius effect across the dayside equatorial magnetopause.
Interdependence of tropical cirrus properties and their variability
Authors: Sunilkumar S. V. , Parameswaran K. , Thampi Bijoy V.
Published: June 2010

Abstract. The mean properties of tropical cirrus, such as cloud top, cloud base, optic centre, cloud strength/optical depth, asymmetry factor and cloud depolarization, as well as their heterogeneities are examined using lidar observations over 281 nights from a tropical station Gadanki (13.5° N, 79.2° E) during the period 1998–2002. This study shows that as the cloud optical depth (τc) increases the cloud becomes more asymmetric in its scattering property. The amount of asymmetry is less than 2% for very low values of (τc and increases nonlinearly with an increase in (τc. The physical properties of these clouds also show significant variation with different time scales during the course of each night. On average, while the short-term variations in (τc are in opposite phase with those of the asymmetry factor (ξ) and volume depolarization ratio (δ), the long-term variation in (τc extending over a night are found to be in opposite phase with that of ξ and in-phase with that of δ. The short-term variations in δ and (τc were attributed to possible changes in the cloud particle orientation and the long period variations to cloud evolution process. The value of δ shows a pronounced variation along the vertical, with low values near the cloud top and cloud base and high values in the middle, which is attributed to the cloud dynamics.
Aerosol transport over the Gangetic basin during ISRO-GBP land campaign-II
Authors: Aloysius M. , Mohan M. , Parameswaran K. , George S. K. , Nair P. R.
Published: June 2010

Abstract. MODIS (Moderate Resolution Imaging Spectroradiometer) Level-3 aerosol optical depth (AOD) data and NCEP (National Centre for Environmental Prediction) reanalysis winds were incorporated into an aerosol flux continuity equation, for a quantitative assessment of the sources of aerosol generation over the Ganga basin in the winter month of December 2004. Preliminary analysis on the aerosol distribution and wind fields showed wind convergence to be an important factor which, supported by the regional topography, confines aerosols in a long band over the Indo Gangetic plain (IGP) stretching from the west of the Thar desert into the Head-Bay-of-Bengal. The prevailing winds of the season carry the aerosols from Head-Bay-of-Bengal along the east coast as far as the southern tip of the peninsular India. A detailed examination of MODIS data revealed significant day-to-day variations in aerosol loading in localised pockets over the central and eastern parts of the Indo Gangetic plain during the second half of December, with AOD values even exceeding unity. Aerosols over the Ganga basin were dominated by fine particles (geometric mean radius ~0.05–0.1μm) while those over the central and western India were dominated by large particles (geometric mean radius ~0.3–0.7μ). Before introducing it into the flux equation, the MODIS derived AOD was validated through a comparison with the ground-based measurements collected at Kharagpur and Kanpur; two stations located over the Ganga basin. The strength of the aerosol generation computed using the flux equation indicated the existence of aerosol sources whose locations almost coincided with the concentration of thermal power plants. The quantitative agreement between the source strength and the power plant concentration, with a correlation coefficient 0.85, pointed to thermal power plants as substantial contributors to the high aerosol loading over the Ganga Basin in winter. The layout of aerosol sources also nearly matched the spatial distribution of the Respirable Suspended Particulate Matter (RSPM), derived from the Central Pollution Control Board (CPCB) data, lending additional support to our inference.
Plasma and fields in the wake of Rhea: 3-D hybrid simulation and comparison with Cassini data
Authors: Roussos E. , Müller J. , Simon S. , Bößwetter A. , Motschmann U. , Krupp N. , Fränz M. , Woch J. , Khurana K. K. , Dougherty M. K.
Published: June 2010

Abstract. Rhea's magnetospheric interaction is simulated using a three-dimensional, hybrid plasma simulation code, where ions are treated as particles and electrons as a massless, charge-neutralizing fluid. In consistency with Cassini observations, Rhea is modeled as a plasma absorbing obstacle. This leads to the formation of a plasma wake (cavity) behind the moon. We find that this cavity expands with the ion sound speed along the magnetic field lines, resulting in an extended depletion region north and south of the moon, just a few Rhea radii (RRh) downstream. This is a direct consequence of the comparable thermal and bulk plasma velocities at Rhea. Perpendicular to the magnetic field lines the wake's extension is constrained by the magnetic field. A magnetic field compression in the wake and the rarefaction in the wake sides is also observed in our results. This configuration reproduces well the signature in the Cassini magnetometer data, acquired during the close flyby to Rhea on November 2005. Almost all plasma and field parameters show an asymmetric distribution along the plane where the corotational electric field is contained. A diamagnetic current system is found running parallel to the wake boundaries. The presence of this current system shows a direct corelation with the magnetic field configuration downstream of Rhea, while the resulting j×B forces on the ions are responsible for the asymmetric structures seen in the velocity and electric field vector fields in the equatorial plane. As Rhea is one of the many plasma absorbing moons of Saturn, we expect that this case study should be relevant for most lunar-type interactions at Saturn.
Advanced intermittent clutter filtering for radar wind profiler: signal separation through a Gabor frame expansion and its statistics
Authors: Lehmann V. , Teschke G.
Published: June 2010

Abstract. A new signal processing method is presented for the suppression of intermittent clutter echoes in radar wind profilers. This clutter type is a significant problem during the seasonal bird migration and often results in large discrepancies between profiler wind measurements and independent reference data. The technique presented makes use of a discrete Gabor frame expansion of the coherently averaged time series data in combination with a statistical filtering approach to exploit the different signal characteristics between signal and clutter. The rationale of this algorithm is outlined and the mathematical methods used are presented in due detail. A first test using data obtained with an operational 482 MHz wind profiler indicates that the method outperforms the previously used clutter suppression algorithm.
Storm-time ionization enhancements at the topside low-latitude ionosphere
Authors: Dmitriev A. , Yeh H.-C.
Published: June 2010

Abstract. Ion density enhancements at the topside low-latitude ionosphere during a Bastille storm on 15–16 July 2000 and Halloween storms on 29–31 October 2003 were studied using data from ROCSAT-1/IPEI experiment. Prominent ion density enhancements demonstrate similar temporal dynamics both in the sunlit and in the nightside hemispheres. The ion density increases dramatically (up to two orders of magnitude) during the main phase of the geomagnetic storms and reaches peak values at the storm maximum. The density enhancements are mostly localized in the region of a South Atlantic Anomaly (SAA), which is characterized by very intense fluxes of energetic particles. The dynamics of near-Earth radiation was studied using SAMPEX/LEICA data on >0.6 MeV electrons and >0.8 MeV protons at around 600 km altitude. During the magnetic storms the energetic particle fluxes in the SAA region and in its vicinity increase more than three orders of magnitude. The location of increased fluxes overlaps well with the regions of ion density enhancements. Two mechanisms were considered to be responsible for the generation of storm-time ion density enhancements: prompt penetration of the interplanetary electric field and abundant ionization of the ionosphere by enhanced precipitation of energetic particles from the radiation belt.
Formation of lower-hybrid solitary structures by modulational interaction between lower-hybrid and dispersive Alfvén waves
Authors: Hall J. O. , Stenberg G. , Eriksson A. I. , André M.
Published: June 2010

Abstract. We investigate the possibility that lower-hybrid solitary structures (LHSS), which are frequently observed in the Earth's ionosphere and magnetosphere, are formed as a result of a modulational interaction between lower-hybrid and dispersive Alfvén waves of initially small amplitude. A large amplitude lower-hybrid pump wave can excite density structures with length scales transverse to the geomagnetic field of the order of the ion gyroradius via a modulational instability. The structure formation in the nonlinear stage of the instability is investigated by numerical solutions of the governing equations, using plasma parameters relevant for LHSS observations in the upper ionosphere and in the magnetosphere. The numerical solutions reveal that the lower-hybrid waves become self-localized inside cylindrically symmetric (with respect to the ambient magnetic field) density cavities, in qualitative agreement with observations. Our model includes thermal electron effects but shows no stabilization at the ion sound gyroradius, suggesting that any preference of observed LHSS for that perpendicular scale likely is due to processes arresting the cavity collapse.
Statistical visualization of the Earth's magnetotail based on Geotail data and the implied substorm model
Authors: Machida S. , Miyashita Y. , Ieda A. , Nosé M. , Nagata D. , Liou K. , Obara T. , Nishida A. , Saito Y. , Mukai T.
Published: June 2010

Abstract. We investigated the temporal and spatial development of the near-Earth magnetotail during substorms based on multi-dimensional superposed-epoch analysis of Geotail data. The start time of the auroral break-up (t=0) of each substorm was determined from auroral data obtained by the Polar and IMAGE spacecraft. The key parameters derived from the plasma, magnetic-field, and electric-field data from Geotail were sorted by their meridional X(GSM)–Z(proxy) coordinates. The results show that the Poynting flux toward the plasma-sheet center starts at least 10 min before the substorm onset, and is further enhanced at X~−12 RE (Earth radii) around 4 min before the onset. Simultaneously, large-amplitude fluctuations occurred, and earthward flows in the central plasma sheet between X~−11 RE and X~−19 RE and a duskward flow around X=−10 RE were enhanced. The total pressure starts to decrease around X=−16 RE about 4 min before the onset of the substorm. After the substorm onset, a notable dipolarization is observed and tailward flows commence, characterised by southward magnetic fields in the form of a plasmoid. We confirm various observable-parameter variations based on or predicted by the relevant substorm models; however, none of these can explain our results perfectly. Therefore, we propose a catapult (slingshot) current-sheet relaxation model, in which an earthward convective flow produced by catapult current-sheet relaxation and a converted duskward flow near the Earth are enhanced through flow braking around 4 min before the substorm onset. These flows induce a ballooning instability or other instabilities, causing the observed current disruption. The formation of the magnetic neutral line is a natural consequence of the present model, because the relaxation of a highly stretched catapult current-sheet produces a very thin current at its tailward edge being surrounded by intense earthward and tailward magnetic fields which were formerly the off-equatorial lobe magnetic fields. This location is the boundary between a highly stressed catapult current sheet and a Harris-type current sheet characterized by little stress. In addition, the flows induced around the boundary toward the current-sheet center may enhance the formation of the magnetic neutral line and the efficiency of magnetic reconnection. After magnetic reconnection is induced, it plays a significant role in driving the substorm.
Reconnection in substorms and solar flares: analogies and differences
Authors: Birn J. , Hesse M.
Published: June 2010

Abstract. Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of a very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares. Further similarities might exist in the role of collapsing magnetic flux tubes, as a consequence of reconnection, in the heating and acceleration of charged particles.
Magnetic-inclination effects in the spectral resonance structure of the ionospheric Alfvén resonator
Authors: Bösinger T. , Ermakova E. N. , Haldoupis C. , Kotik D. S.
Published: June 2010

Abstract. Based on recent developments in the formalism governing the spectral resonance structures (SRS) of the Ionospheric Alfvén resonator (IAR) as observed on the Earth's surface, a numerical code was developed to investigate properties of SRS which can in particular be contributed to magnetic inclination effects. Among the theoretical findings are: 1) SRS is discernible in both orthogonal components, 2) the harmonic structure of SRS is not anymore over frequency equidistantly distributed, 3) the frequency scales of SRS differ in the two normal modes. The theoretically predicted properties could be found in the observations of a low latitude and some of them even in the data of a mid latitude station. The verification, however, is not as straight forward because the predicted effects do not only depend on magnetic inclination but also on the wave angle of the lightning induced electromagnetic wave k-vector with the normal to the magnetic meridian passing through the observation site. So far the formalism is simplified as it deals with a single source situation alone whereas the actual observation is a composite of excitations caused by an average of about 60 flashes of lightning operating all the time, world-wide.
Spatial variation of eddy-diffusion coefficients in the turbulent plasma sheet during substorms
Authors: Stepanova M. , Antonova E. E. , Paredes-Davis D. , Ovchinnikov I. L. , Yermolaev Y. I.
Published: June 2010

Abstract. Study of the plasma turbulence in the central plasma sheet was performed using the Interball-Tail satellite data. Fluctuations of the plasma bulk velocity in the plasma sheet were deduced from the measurements taken by the Corall instrument for different levels of geomagnetic activity and different locations inside the plasma sheet. The events that satisfied the following criteria were selected for analysis: number density 0.1–10 cm−3, ion temperature T≥0.3 keV, and average bulk velocity ≤100 km/s. It was found that the plasma sheet flow generally appears to be strongly turbulent, i.e. is dominated by fluctuations that are unpredictable. Corresponding eddy-diffusion coefficients in Y- and Z-direction in the GSM coordinate system were derived using the autocorrelation time and rms velocity. Statistical studies of variation of the eddy-diffusion coefficients with the location inside the plasma sheet showed a significant increase in these coefficients in the tailward direction. During substorms this dependence shows strong increase of eddy-diffusion in the central part of the plasma sheet at the distances of 10–30 Earth's radii. This effect is much stronger for Y-components of the eddy-diffusion coefficient, which could be related to the geometry of the plasma sheet, allowing more room for development of eddies in this direction.
Dual source populations of substorm-associated ring current ions
Authors: Yamauchi M. , Ebihara Y. , Dandouras I. , Rème H.
Published: June 2010

Abstract. Sources of low-energy ring current ions in the early morning sector (eastward drifting energy domain of about <5 keV) are examined using both statistical analyses and numerical tracing methods (phase-space mapping and simulation). In about 90% of Cluster perigee traversals at 02~07 local time, these low-energy ring current ions have dual ion populations: one is wedge-like energy-dispersed ions, and the other is a band-like ions over different latitudes in a narrow energy range at the upper energy threshold of the wedge-like energy-dispersed ions. Both components are most likely created during past substorm activities. Numerical tracing results strongly suggest that these two components have different sources with different temperatures and elapsed times. The band-like part most likely comes from ions with plasma sheet temperature (~1 keV), and the energy-dispersed part most likely comes from cold ions (temperature <0.1 keV). The source density of the cold component (0.2~0.5×106/m3) is slightly less than that of the hot component (0.5×106/m3), while Cluster observation shows slightly higher density for the wedge-like part than the low-energy band-like part. The hot source component also explains the observed high-energy (>10 keV) ions drifting westward after adiabatic energization in the nightside under time-varying electric field. The wedge-like part has much shorter elapsed time, i.e., less charge-exchange loss, than the band-like part.
The first GPS-TEC imaging of the space structure of MS wave packets excited by the solar terminator
Authors: Afraimovich E. L. , Edemskiy I. K. , Voeykov S. V. , Yasyukevich Yu. V. , Zhivetiev I. V.
Published: June 2010

Abstract. Using TEC measurements from the dense network of GPS sites GEONET, we have obtained the first GPS-TEC image of the space structure of medium-scale traveling wave packets (MS TWP) excited by the morning solar terminator (ST). We found that ST-generated wave packets have duration of about 1–2 h and time shift of about 1.5–6 h after the morning ST appearance at an altitude of 300 km. The TWP wave front extends along the morning ST line with the angular shift of about 20°. The time period and wave-length of ST-generated wave packets are about 10–20 min and 200–300 km, respectively. The velocity of the TWP phase front traveling is of about 300 m/s. The space image of MS TWP manifests itself in pronounced anisotropy and high coherence over a long distance of about 2000 km.
Characteristics of equatorial gravity waves derived from mesospheric airglow imaging observations
Authors: Suzuki S. , Shiokawa K. , Liu A. Z. , Otsuka Y. , Ogawa T. , Nakamura T.
Published: June 2010

Abstract. We present the characteristics of small-scale (<100 km) gravity waves in the equatorial mesopause region derived from OH airglow imaging observations at Kototabang (100.3° E, 0.2° S), Indonesia, from 2002 to 2005. We adopted a method that could automatically detect gravity waves in the airglow images using two-dimensional cross power spectra of gravity waves. The propagation directions of the waves were likely controlled by zonal filtering due to stratospheric mean winds that show a quasi-biennial oscillation (QBO) and the presence of many wave sources in the troposphere.
The ionospheric behavior in conjugate hemispheres during the 3 October 2005 solar eclipse
Authors: Le H. , Liu L. , Yue X. , Wan W.
Published: June 2010

Abstract. We investigate the ionospheric behavior in conjugate hemispheres during the 3 October 2005 solar eclipse, on the basis of observations of electron temperature (Te) from the Defense Meteorological Satellites Program (DMSP) spacecraft, F2 layer critical frequency (foF2) and F2 layer peak height (hmF2) at the Grahamstown ionosonde station, and total electron content (TEC) from the Global Positioning System (GPS) station SUTH. The observations show that when the eclipse occurred in the Northern Hemisphere, there was a decrease in Te, an increase in foF2 and TEC, and an uprising in hmF2 in its conjugate region compared with their reference values. We also simulated the ionosphere behavior during this eclipse using a mid- and low-latitude ionospheric model. The simulations agree well with the observations. Because of the eclipse effect, there are far fewer photoelectrons travelling along the magnetic field lines from the eclipse region to the conjugate region, resulting in reduced photoelectron heating in the conjugate hemisphere which causes a drop in electron temperature and subsequent disturbances in the region.