bluuebunny/crossref_metadata_2025 huggingface dataset:
Increased electric sail thrust through removal of trapped shielding electrons by orbit chaotisation due to spacecraft body
Authors: Janhunen P.
Published: June 2010

Abstract. An electric solar wind sail is a recently introduced propellantless space propulsion method whose technical development has also started. The electric sail consists of a set of long, thin, centrifugally stretched and conducting tethers which are charged positively and kept in a high positive potential of order 20 kV by an onboard electron gun. The positively charged tethers deflect solar wind protons, thus tapping momentum from the solar wind stream and producing thrust. The amount of obtained propulsive thrust depends on how many electrons are trapped by the potential structures of the tethers, because the trapped electrons tend to shield the charged tether and reduce its effect on the solar wind. Here we present physical arguments and test particle calculations indicating that in a realistic three-dimensional electric sail spacecraft there exist a natural mechanism which tends to remove the trapped electrons by chaotising their orbits and causing them to eventually collide with the conducting tethers. We present calculations which indicate that if these mechanisms were able to remove trapped electrons nearly completely, the electric sail performance could be about five times higher than previously estimated, about 500 nN/m, corresponding to 1 N thrust for a baseline construction with 2000 km total tether length.
Low latitude ionospheric effects of major geomagnetic storms observed using TOPEX TEC data
Authors: Migoya-Orué Y. O. , Radicella S. M. , Coïsson P.
Published: June 2010

Abstract. Low latitude ionospheric effects of two major geomagnetic storms are analysed using TOPEX TEC data for specific satellite passes. The storms are the one that started on 15 July 2000 and the one that started on 8 November 2004. The variation of vertical TEC as a function of latitude along the satellite passes during day-time mostly in the region of the Pacific Ocean have been analysed comparing the storm period with quiet conditions. It has to be noted that for obvious reasons the TEC behaviour over this region cannot be observed using ground-based instruments but TOPEX data give a reasonable overall view of the region covered by the Equatorial Anomaly, just as the storms were developing. The performance of vertical TEC obtained from GPS derived TEC of global ionospheric maps (GIMs) are compared with the TOPEX data in order to determine their accuracy when storms of this type take place. The results show that the Equatorial Anomaly TEC peaks move towards the poles by several degrees and increase their intensity with respect to the quiet conditions behaviour for both storms that occurred at different seasons and solar activity level. This behaviour is not well represented by the maps of the different GIMs used in this study. The rate of change obtained from TOPEX TEC were computed to look for vertical TEC spatial gradients variations.
Analysis of three-spacecraft data using planar reciprocal vectors: methodological framework and spatial gradient estimation
Authors: Vogt J. , Albert A. , Marghitu O.
Published: June 2010

Abstract. In the context of ESA's Cluster mission, four-point array techniques are widely used to analyze space plasma phenomena such as shocks and discontinuities, waves and turbulence, and spatial gradients. Due to failures of single instruments on the Cluster spacecraft fleet, there is also need for array processing of three-point measurements. In this paper we identify planar reciprocal vectors as a generic tool for this purpose. The class of three-point techniques introduced here includes methods for discontinuity analysis, wave identification, and spatial gradient determination. Parameter vectors can be resolved fully in the spacecraft plane but further assumptions or physical constraints have to be specified to estimate the normal components. We focus on the gradient estimation problem where we check and illustrate our approach using Cluster measurements.
Small-scale characteristics of extremely high latitude aurora
Authors: Cumnock J. A. , Blomberg L. G. , Kullen A. , Karlsson T. ,   K. Å. T. Sundberg
Published: June 2010

Abstract. We examine 14 cases of an interesting type of extremely high latitude aurora as identified in the precipitating particles measured by the DMSP F13 satellite. In particular we investigate structures within large-scale arcs for which the particle signatures are made up of a group of multiple distinct thin arcs. These cases are chosen without regard to IMF orientation and are part of a group of 87 events where DMSP F13 SSJ/4 measures emissions which occur near the noon-midnight meridian and are spatially separated from both the dawnside and duskside auroral ovals by wide regions with precipitating particles typical of the polar cap. For 73 of these events the high-latitude aurora consists of a continuous region of precipitating particles. We focus on the remaining 14 of these events where the particle signatures show multiple distinct thin arcs. These events occur during northward or weakly southward IMF conditions and follow a change in IMF By. Correlations are seen between the field-aligned currents and plasma flows associated with the arcs, implying local closure of the FACs. Strong correlations are seen only in the sunlit hemisphere. The convection associated with the multiple thin arcs is localized and has little influence on the large-scale convection. This also implies that the sunward flow along the arcs is unrelated to the overall ionospheric convection.
Real-time 3-D hybrid simulation of Titan's plasma interaction during a solar wind excursion
Authors: Simon S.
Published: June 2010

Abstract. The plasma environment of Saturn's largest satellite Titan is known to be highly variable. Since Titan's orbit is located within the outer magnetosphere of Saturn, the moon can leave the region dominated by the magnetic field of its parent body in times of high solar wind dynamic pressure and interact with the thermalized magnetosheath plasma or even with the unshocked solar wind. By applying a three-dimensional hybrid simulation code (kinetic description of ions, fluid electrons), we study in real-time the transition that Titan's plasma environment undergoes when the moon leaves Saturn's magnetosphere and enters the supermagnetosonic solar wind. In the simulation, the transition between both plasma regimes is mimicked by a reversal of the magnetic field direction as well as a change in the composition and temperature of the impinging plasma flow. When the satellite enters the solar wind, the magnetic draping pattern in its vicinity is reconfigured due to reconnection, with the characteristic time scale of this process being determined by the convection of the field lines in the undisturbed plasma flow at the flanks of the interaction region. The build-up of a bow shock ahead of Titan takes place on a typical time scale of a few minutes as well. We also analyze the erosion of the newly formed shock front upstream of Titan that commences when the moon re-enters the submagnetosonic plasma regime of Saturn's magnetosphere. Although the model presented here is far from governing the full complexity of Titan's plasma interaction during a solar wind excursion, the simulation provides important insights into general plasma-physical processes associated with such a disruptive change of the upstream flow conditions.
Light absorption by pollution, dust, and biomass burning aerosols: a global model study and evaluation with AERONET measurements
Authors:   Mian Chin, Diehl T. , Dubovik O. , Eck T. F. , Holben B. N. , Sinyuk A. , Streets D. G.
Published: June 2010

Abstract. Atmospheric aerosol distributions from 2000 to 2007 are simulated with the Goddard Chemistry Aerosol Radiation and Transport (GOCART) model to attribute light absorption by aerosol to its composition and sources from pollution, dust, and biomass burning. The 8-year, global averaged total aerosol optical depth (τ), absorption optical depth (τa), and single scattering albedo (ω) at 550 nm are estimated at 0.14, 0.0086, and 0.95, respectively, with sulfate making the largest fraction of τ (37%), followed by dust (30%), sea salt (16%), organic matter (OM) (13%), and black carbon (BC) (4%). BC and dust account for 43% and 53% of τa, respectively. From a model experiment with "tagged" sources, natural aerosols are estimated to be 58% of τ and 53% of τa, with pollution and biomass burning aerosols to share the rest. Comparing with data from the surface sunphotometer network AERONET, the model tends to reproduce much better the AERONET direct measured data of τ and the Ångström exponent (α) than its retrieved quantities of ω and τa. Relatively small in its systematic bias of τ for pollution and dust regions, the model tends to underestimate τ for biomass burning aerosols by 30–40%. The modeled α is 0.2–0.3 too low (particle too large) for pollution and dust aerosols but 0.2–0.3 too high (particle too small) for the biomass burning aerosols, indicating errors in particle size distributions in the model. Still, the model estimated ω is lower in dust regions and shows a much stronger wavelength dependence for biomass burning aerosols but a weaker one for pollution aerosols than those quantities from AERONET. These comparisons necessitate model improvements on aerosol size distributions, the refractive indices of dust and black carbon aerosols, and biomass burning emissions in order to better quantify the aerosol absorption in the atmosphere.
Resonance scattering by auroral N2+: steady state theory and observations from Svalbard
Authors: Jokiaho O. , Lanchester B. S. , Ivchenko N.
Published: June 2010

Abstract. Studies of auroral energy input at high latitudes often depend on observations of emissions from the first negative band of ionised nitrogen. However, these emissions are affected by solar resonance scattering, which makes photometric and spectrographic measurements difficult to interpret. This work is a statistical study from Longyearbyen, Svalbard, Norway, during the solar minimum between January and March 2007, providing a good coverage in shadow height position and precipitation conditions. The High Throughput Imaging Echelle Spectrograph (HiTIES) measured three bands of N2+ 1N (0,1), (1,2) and (2,3), and one N2 2P band (0,3) in the magnetic zenith. The brightness ratios of the N2+ bands are compared with a theoretical treatment with excellent results. Balance equations for all important vibrational levels of the three lowest electronic states of the N2+ molecule are solved for steady-state, and the results combined with ion chemistry modelling. Brightnesses of the (0,1), (1,2) and (2,3) bands of N2+ 1N are calculated for a range of auroral electron energies, and different values of shadow heights. It is shown that in sunlit aurora, the brightness of the (0,1) band is enhanced, with the scattered contribution increasing with decreasing energy of precipitation (10-fold enhancements for energies of 100 eV). The higher vibrational bands are enhanced even more significantly. In sunlit aurora the observed 1N (1,2)/(0,1) and (2,3)/(0,1) ratios increase as a function of decreasing precipitation energy, as predicted by theory. In non-sunlit aurora the N2+ species have a constant proportionality to neutral N2. The ratio of 2P(0,3)/1N(0,1) in the morning hours shows a pronounced decrease, indicating enhancement of N2+ 1N emission. Finally we study the relationship of all emissions and their ratios to rotational temperatures. A clear effect is observed on rotational development of the bands. It is possible that greatly enhanced rotational temperatures may be a signature of ion upflows.
Plasma boundary variability at Mars as observed by Mars Global Surveyor and Mars Express
Authors: Edberg N. J. T. , Brain D. A. , Lester M. , Cowley S. W. H. , Modolo R. , Fränz M. , Barabash S.
Published: June 2010

Abstract. We have used Mars Express (MEX) and Mars Global Surveyor (MGS) simultaneous and non-simultaneous measurements to study the Martian plasma environment. In particular, we have derived quantitative expressions for the altitude of the terminator bow shock (BS) and magnetic pileup boundary (MPB) as functions of solar wind dynamic pressure, crustal magnetic fields and solar EUV flux. We have also studied the influence of the interplanetary magnetic field (IMF) direction. Through simultaneous two-spacecraft case studies we have shown that the dynamic pressure has a strong influence on the location and shape of these boundaries, which is also confirmed through a large statistical study. A higher dynamic pressure pushes the boundaries downward. The IMF direction has a weaker but still significant influence on both boundaries and causes them to move outward in the hemisphere of locally upward electric field. However, the MPB in the Southern Hemisphere is found to actually move inward when the electric field is directed locally upward. The crustal magnetic fields in the Southern Hemisphere have a strong influence on the MPB and cause it to move to higher altitudes over strong crustal magnetic fields. The influence of the crustal magnetic fields on the BS is more ambiguous since there are few crossings over the strongest crustal fields, but there appears to be at least a small trend of a higher BS for stronger crustal fields. An increased solar EUV flux has been found to cause the BS to move outward and the MPB to move inward.
Fog deposition to a Tillandsia carpet in the Atacama Desert
Authors: Westbeld A. , Klemm O. , Grießbaum F. , Sträter E. , Larrain H. , Osses P. , Cereceda P.
Published: June 2010

Abstract. In the Atacama Desert, one of the driest places on earth, fog deposition plays an important role for the water balance and for the survival of vulnerable ecosystems. The eddy covariance method, previously applied for the quantification of fog deposition to forests in various parts of the world, was used for the first time to measure deposition of fog water to a desert. In this exploratory study we estimate the amount of water available for the ecosystem by deposition and determine the relevant processes driving fog deposition. This is especially important for the species Tillandsia landbecki living in coastal Atacama at the limit of plant existence with fog and dew being the only sources of water. Between 31 July and 19 August 2008 approximately 2.5 L m−2 of water were made available through deposition. Whole-year deposition was estimated as 25 L m−2. Turbulent upward fluxes occurred several times during the evenings and are explained by the formation of radiation fog. In connection with that, underestimates of the deposition are assumed. More detailed studies covering various seasons and all parameters and fluxes contributing to the local energy balance are suggested. This will help to further develop understanding about the processes of (i) deposition of water to the desert, and (ii) intensification of advection fog through additional formation of radiation fog.
Climatology of planetary wave type oscillations with periods of 2–20 days derived from O2 atmospheric and OH(6-2) airglow observations at mid-latitude with SATI
Authors: López-González M. J. , Rodríguez E. , García-Comas M. , Costa V. , Shepherd M. G. , Shepherd G. G. , Aushev V. M. , Sargoytchev S.
Published: June 2010

Abstract. The presence of planetary wave type oscillations at mid-latitudes in the mesosphere/lower thermosphere region has been investigated using airglow observations. The observations were taken with a Spectral Airglow Temperature Imager (SATI) installed at Sierra Nevada Observatory (37.06° N, 3.38° W) at 2900 m height. Airglow data of the column emission rate of the O2 Atmospheric (0-1) band and of the OH Meinel (6-2) band and deduced rotational temperatures from 1998 to 2007 have been used in this study. From these observations a climatology of planetary wave type oscillations at this location is inferred. It has been found that the planetary wave type oscillations of 5-day period is predominant in our data throughout the year, with activity greater than 50% during March/April and October/November months. The planetary wave type oscillations of 2-day period is predominant during both solstices, being predominant during winter solstice in O2 while a 10-day oscillation appears throughout the year with activity around 20% and with maximum activity during spring and autumn equinoxes. The 16-day oscillation has maximum occurrence during autumn-winter while its activity is almost disappeared during spring-summer. No clear seasonal dependence of the amplitude of the planetary wave type oscillations was observed in the cases considered in this study. The waves simultaneously detected in the rotational temperatures deduced from both OH and O2 emissions usually show an upward energy propagation and are affected by dissipation processes.
Statistical characteristics of AGW wave packet propagation in the lower atmosphere observed by the MU radar
Authors: Kuo F. S. , Lue H. Y. , Fern C. L. , Röttger J. , Fukao S. , Yamamoto M.
Published: June 2010

Abstract. We study the horizontal structure of the atmospheric gravity waves (AGW) in the height ranges between 6 and 22 km observed using the MU radar at Shigaraki in Japan, during a 3 day period in January and a 4 day period in August 1988. The data were divided by double Fourier transformation into a data set of upward moving waves and a data set of downward moving waves for independent analysis. The phase and group velocity tracing technique was applied to measure the vertical group and phase velocity as well as the characteristic period of the gravity wave packet. Then the dispersion equation of the linear theory of AGW was solved to obtain its intrinsic wave period – horizontal wavelength and horizontal group velocity – and the vertical flux of horizontal momentum associated with each wave packet was estimated to help determine the direction of the characteristic horizontal wave vector. The results showed that the waves with periods in the range of 30 min~6 h had horizontal scales ranging from 20 km to 1500 km, vertical scales from 4 km to 15 km, and horizontal phase velocities from 15 m/s to 60 m/s. The upward moving wave packets of wave period of 2 h~6 h had horizontal group velocities mainly toward east-south-east and northeast in winter, and mainly in the section between the directions of west-north-west and north in summer.
Magnetosheath cavities: case studies using Cluster observations
Authors: Katırcıoğlu F. T. , Kaymaz Z. , Sibeck D. G. , Dandouras I.
Published: June 2010

Abstract. This paper presents examples of magnetosheath cavities in Cluster spacecraft observations. The cavities are accompanied by high energy particles in the magnetosheath and characterized by depressed magnetic fields and densities. Flow speeds decrease and temperatures increase within the cavities. All magnetosheath parameters show increased variability within the cavities when the energetic particle flux is high. We predict outward motion of the magnetopause boundary in response to the decreases in the magnetosheath ram pressure caused by the high energy particles within the magnetosheath cavities. For our events, the magnetopause distance is predicted to be 30% larger during the times of high energy particle flux in the magnetosheath than that predicted using concurrent upstream solar wind pressure observations. Our events show no preference to occur for a particular IMF direction or solar wind plasma condition.
Electrodynamical response of the Indian low-mid latitude ionosphere to the very large solar flare of 28 October 2003 – a case study
Authors: Manju G. , Pant T. K. , Devasia C. V. , Ravindran S. , Sridharan R.
Published: June 2010

Abstract. The electrodynamic effects on the low-mid latitude ionospheric region have been investigated using GPS (global positioning system) data, ionosonde data and ΔH values, during the very large solar flare (X17.2/4B) of 28 October 2003. The results bring out the flare induced unusual behaviour of the equatorial ionosphere on this day just prior to sunset. The important observations are i) Large and prolonged Ne enhancements observed from ionosonde data just after the flare-related peak enhancement in EUV flux. The observed enhancement in Ne is due to the increase in ionization production due to the enhanced EUV flux and the persistence of the enhancement is probably due to the prompt penetration related upliftment of the F layer (just prior to the flare peak phase) to higher altitudes, where recombination rates are lower. ii) A significant enhancement in total electron content (TEC) (~10 TEC units) at regions around the Equatorial Ionization Anomaly (EIA) crest region (Ahmedabad) during the flare in association with the flare related EUV flux enhancement. iii) Similar enhancements seen at stations of Jodhpur and Delhi in the mid latitude sector. iv)The flare related flux enhancements in different longitude sectors in the equatorial electrojet region have been shown to produce positive and negative variations in electrojet strength indicating the presence of current systems having positive and negative polarities in different longitude sectors. Thus the flare effect reveals the longitudinal variation of the counter electrojet events in the Equatorial Electrojet (EEJ) region.
Characteristics of the ionospheric total electron content of the equatorial ionization anomaly in the Asian-Australian region during 1996–2004
Authors:   Biqiang Zhao,   Weixing Wan,   Libo Liu,   Zhipeng Ren
Published: June 2010

Abstract. Ionospheric total electron content (TEC) of the equatorial ionization anomaly (EIA) is studied by analyzing dual-frequency signals of the Global Position System (GPS) acquired from a network of receivers around the Asian-Australian region during 1996–2004. The latitude, occurrence time, strength of the most developed EIA crest, and crest-to-trough ratio (CTR) for both the noon and post-sunset sector obtained from a daily TEC contour map have been used to study the solar cycle variations of EIA in the Asian-Australian region. The results reveal that semiannual and seasonal variations were the dominant factor that controls the morphology of the EIA structure which can be identified in the past studies (e.g. Wu et al., 2008). It is also found that the latitude and local time position of the anomaly crest show a hemispheric asymmetry because (a) The northern crest of EIA is expanded during the equinox indicating a weak semiannual variation while the southern crest is inhibited during June–August presenting a strong seasonal variation, and (b) The local time of the northern crest appears ~1.3 h earlier than that of the southern crest in June while showing no difference at December. Solar activity dependence is more evident in the EIA crest region than in the EIA trough region and least in the post-sunset sector at equinox. A seasonal linear relationship is derived between the post-sunset CTR and solar flux, which should be caused by the solar-dependant equatorial E×B vertical drift.
Speed evolution of fast CME/shocks with SOHO/LASCO, WIND/WAVES, IPS and in-situ WIND data: analysis of kilometric type-II emissions
Authors: Gonzalez-Esparza A. , Aguilar-Rodriguez E.
Published: June 2010

Abstract. Fast CME/shocks propagating in the interplanetary medium can generate kilometric Type II (km-TII) radio emissions at the local plasma frequency and/or its harmonic, so these radio emissions provide a means of remotely tracking CME/shocks. We apply a new analysis technique, using the frequency drift of km-TII spectrum obtained by the Thermal Noise Receiver (TNR) of the WIND/WAVES experiment, to infer, at some adequate intervals, the propagation speed of six CME/shocks. We combine these results with previously reported speeds from coronagraph white light and interplanetary scintillation observations, and in-situ measurements, to study the temporal speed evolution of the six events. The speed values obtained by the km-TII analysis are in a reasonable agreement with the speed measurements obtained by other techniques at different heliocentric distance ranges. The combination of all the speed measurements show a gradual deceleration of the CME/shocks as they propagate to 1 AU. This new technique can be useful in studying the evolution of fast CME/shocks when adequate intervals of km-TII emissions are available.
Evaluation of magnetic helicity density in the wave number domain using multi-point measurements in space
Authors: Narita Y. , Kleindienst G. , Glassmeier K.-H.
Published: June 2010

Abstract. We develop an estimator for the magnetic helicity density, a measure of the spiral geometry of magnetic field lines, in the wave number domain as a wave diagnostic tool based on multi-point measurements in space. The estimator is numerically tested with a synthetic data set and then applied to an observation of magnetic field fluctuations in the Earth foreshock region provided by the four-point measurements of the Cluster spacecraft. The energy and the magnetic helicity density are determined in the frequency and the wave number domain, which allows us to identify the wave properties in the plasma rest frame correcting for the Doppler shift. In the analyzed time interval, dominant wave components have parallel propagation to the mean magnetic field, away from the shock at about Alfvén speed and a left-hand spatial rotation sense of helicity with respect to the propagation direction, which means a right-hand temporal rotation sense of polarization. These wave properties are well explained by the right-hand resonant beam instability as the driving mechanism in the foreshock. Cluster observations allow therefore detailed comparisons with various theories of waves and instabilities.
Separatrix regions of magnetic reconnection at the magnetopause
Authors: Lindstedt T. , Khotyaintsev Yu. V. , Vaivads A. , André M. , Fear R. C. , Lavraud B. , Haaland S. , Owen C. J.
Published: June 2010

Abstract. Using data from the four Cluster spacecraft we study the separatrix regions of magnetic reconnection sites at the dayside magnetopause under conditions when reconnection is occurring in the magnetopause current layer which separates magnetosheath plasma from the hot magnetospheric plasma sheet. We define the separatrix region as the region between the separatrix – the first field line opened by reconnection – and the reconnection jet (outflow region). We analyze eight separatrix region crossings on the magnetospheric side of the magnetopause and present detailed data for two of the events. We show that characteristic widths of the separatrix regions are of the order of ten ion inertial lengths at the magnetopause. Narrow separatrix regions with widths comparable to a few ion inertial lengths are rare. We show that inside the separatrix region there is a density cavity which sometimes has complex internal structure with multiple density dips. Strong electric fields exist inside the separatrix regions and the electric potential drop across the regions can be up to several kV. On the magnetosheath side of the region there is a density gradient with strong field aligned currents. The observed strong electric fields and currents inside the separatrix region can be important for a local energization of ions and electrons, particularly of ionospheric origin, as well as for magnetosphere-ionosphere coupling.
The expected imprint of flux rope geometry on suprathermal electrons in magnetic clouds
Authors: Owens M. J. , Crooker N. U. , Horbury T. S.
Published: June 2010

Abstract. Magnetic clouds are a subset of interplanetary coronal mass ejections characterized by a smooth rotation in the magnetic field direction, which is interpreted as a signature of a magnetic flux rope. Suprathermal electron observations indicate that one or both ends of a magnetic cloud typically remain connected to the Sun as it moves out through the heliosphere. With distance from the axis of the flux rope, out toward its edge, the magnetic field winds more tightly about the axis and electrons must traverse longer magnetic field lines to reach the same heliocentric distance. This increased time of flight allows greater pitch-angle scattering to occur, meaning suprathermal electron pitch-angle distributions should be systematically broader at the edges of the flux rope than at the axis. We model this effect with an analytical magnetic flux rope model and a numerical scheme for suprathermal electron pitch-angle scattering and find that the signature of a magnetic flux rope should be observable with the typical pitch-angle resolution of suprathermal electron data provided ACE's SWEPAM instrument. Evidence of this signature in the observations, however, is weak, possibly because reconnection of magnetic fields within the flux rope acts to intermix flux tubes.
High latitude magnetospheric topology and magnetospheric substorm
Authors: Antonova E. E. , Kirpichev I. P. , Ovchinnikov I. L. , Orlova K. G. , Stepanova M. V.
Published: June 2010

Abstract. This study is focused on the problem of the localization of substorm expansion onset. In this context, the high latitude topology of transverse magnetospheric currents has been analyzed. This study has included the radial distribution of plasma pressure near noon, obtained using the THEMIS-B satellite data, the daytime compression of magnetic field lines and the existence of magnetic field minima far from the equatorial plane, given by all geomagnetic field models. As a result, the dayside integral transverse currents at the geocentric distances 7–10 RE has been estimated. It is suggested, that nightside transverse currents at geocentric distances ~7–10 RE are closed inside the magnetosphere and with dayside transverse currents form surrounding the Earth current system (cut ring current or CRC) which topologically is the high latitude continuation of ordinary ring current. A possibility of localization of substorm expansion onset at the nighside CRC region is analyzed using the experimental evidences that the onset is localized at geocentric distances <10 RE.
Thin embedded current sheets: Cluster observations of ion kinetic structure and analytical models
Authors: Artemyev A. V. , Petrukovich A. A. , Zelenyi L. M. , Nakamura R. , Malova H. V. , Popov V. Y.
Published: June 2010

Abstract. Kinetic structure of embedded thin horizontal current sheets is investigated. Current density estimated by curlometer technique is in general agreement with a sum of electron and proton currents. Embedding of observed thin current sheets in the much wider plasma sheet is apparent in the current density profiles. Ion velocity distributions consist of two parts: the cold non-drifting core likely belongs to the plasma sheet background, while the hotter asymmetric "wings" carry the main portion of the current. Oxygen ions (if present) and higher-energy tails of distribution function can contribute up to 30% of the total current. We compared current density profiles across sheets with three typical current sheet models. Models which allow embedding, describe observed structures equally well at the level of experimental accuracy.
Black Carbon and West African Monsoon precipitation: observations and simulations
Authors: Huang J. , Adams A. , Wang C. , Zhang C.
Published: June 2010

Abstract. We have recently investigated large-scale co-variability between aerosol and precipitation and other meteorological variables in the West African Monsoon (WAM) region using long term satellite observations and reanalysis data. In this study we compared the observational results to a global model simulation including only direct radiative forcing of black carbon (BC). From both observations and model simulations we found that in boreal cold seasons anomalously high African aerosols are associated with significant reductions in cloud amount, cloud top height, and surface precipitation. These results suggest that the observed precipitation reduction in the WAM region is caused by radiative effect of BC. The result also suggests that the BC effect on precipitation is nonlinear.
Refractive index effects on the scatter volume location and Doppler velocity estimates of ionospheric HF backscatter echoes
Authors: Ponomarenko P. V. , St-Maurice J.-P. , Waters C. L. , Gillies R. G. , Koustov A. V.
Published: June 2010

Abstract. Ionospheric E×B plasma drift velocities derived from the Super Dual Auroral Radar Network (SuperDARN) Doppler data exhibit systematically smaller (by 20–30%) magnitudes than those measured by the Defence Meteorological Satellites Program (DMSP) satellites. A part of the disagreement was previously attributed to the change in the E/B ratio due to the altitude difference between the satellite orbit and the location of the effective scatter volume for the radar signals. Another important factor arises from the free-space propagation assumption used in converting the measured Doppler frequency shift into the line-of-sight velocity. In this work, we have applied numerical ray-tracing to identify the location of the effective scattering volume of the ionosphere and to estimate the ionospheric refractive index. The simulations show that the major contribution to the radar echoes should be provided by the Pedersen and/or escaping rays that are scattered in the vicinity of the F-layer maximum. This conclusion is supported by a statistical analysis of the experimental elevation angle data, which have a signature consistent with scattering from the F-region peak. A detailed analysis of the simulations has allowed us to propose a simple velocity correction procedure, which we have successfully tested against the SuperDARN/DMSP comparison data set.
Observational evidence for the plausible linkage of Equatorial Electrojet (EEJ) electric field variations with the post sunset F-region electrodynamics
Authors: Sreeja V. , Devasia C. V. ,   Sudha Ravindran,   Tarun Kumar Pant
Published: June 2010

Abstract. The paper is based on a detailed observational study of the Equatorial Spread F (ESF) events on geomagnetically quiet (Ap≤20) days of the solar maximum (2001), moderate (2004) and minimum (2006) years using the ionograms and magnetograms from the magnetic equatorial location of Trivandrum (8.5° N; 77° E; dip lat ~0.5° N) in India. The study brings out some interesting aspects of the daytime Equatorial Electrojet (EEJ) related electric field variations and the post sunset F-region electrodynamics governing the nature of seasonal characteristics of the ESF phenomena during these years. The observed results seem to indicate a plausible linkage of daytime EEJ related electric field variations with pre-reversal enhancement which in turn is related to the occurrence of ESF. These electric field variations are shown to be better represented through a parameter, termed as "E", in the context of possible coupling between the E- and F-regions of the ionosphere. The observed similarities in the gross features of the variations in the parameter "E" and the F-region vertical drift (Vz) point towards the potential usage of the EEJ related parameter "E" as an useful index for the assessment of Vz prior to the occurrence of ESF.
The Earth's magnetopause as a source and sink for equatorial nightside energetic charged particles
Authors: Klida M. M. , Fritz T. A.
Published: June 2010

Abstract. The Imaging Proton Spectrometer (IPS) and the Imaging Electron Spectrometer (IES) on the Polar satellite have measured temporary deviations in the isotropy of the pitch angle distributions (PADs) of charged particles in the inner magnetosphere. As Polar passes through the nightside equatorial region, the IPS and IES observe dropouts of charged particles with pitch angles near 90°, known as butterfly distributions caused by the shadowing of the magnetopause. Additionally, Polar observes a lower energy (<60 keV) intensification of locally mirroring ions while simultaneously detecting butterfly PADs in both higher energy ions and electrons. While it is accepted that charged particles can be lost to the magnetopause due to shadowing effects, the modeling here can suggest that the magnetopause can also be a direct source for particles observed in magnetosphere, with a strong dependence upon both pitch angle and particle energy.
THEMIS ground-space observations during the development of auroral spirals
Authors: Keiling A. , Angelopoulos V. , Weygand J. M. , Amm O. , Spanswick E. , Donovan E. , Mende S. , McFadden J. , Larson D. , Glassmeier K.-H. , Auster H. U.
Published: June 2010

Abstract. A simultaneous observation of an auroral spiral and its generator region in the near-Earth plasma sheet is rather unlikely. Here we present such observations using the THEMIS spacecraft as well as the THEMIS ground network of all-sky imagers and magnetometers. Two consecutive auroral spirals separated by approximately 14 min occurred during a substorm on 19 February 2008. The spirals formed during the expansion phase and a subsequent intensification, and were among the brightest features in the aurora with diameters of 200–300 km. The duration for the formation and decay of each spiral was less than 60 s. Both spirals occurred shortly after the formation of two oppositely rotating plasma flow vortices in space, which were also accompanied by dipolarizations and ion injections, at ~11 RE geocentric distance. Observations and model calculations also give evidence for a magnetic-field-aligned current generation of approximately 0.1 MA via the flow vortices, connecting the generator region of the spirals with the ionosphere, during the formation of both spirals. In the ionosphere, a pair of equivalent ionospheric current (EIC) vortices with opposite rotations (corresponding to upward and downward currents) was present during both auroral spirals with enhanced EICs and ionospheric flows at the locations of the auroral spirals and along the auroral arcs. The combined ground and space observations suggest that each auroral spiral was powered by two oppositely rotating plasma flow vortices that caused a current enhancement in the substorm current wedge.
Oxygen ion escape from Venus in a global hybrid simulation: role of the ionospheric O+ ions
Authors: Jarvinen R. , Kallio E. , Janhunen P. , Barabash S. , Zhang T. L. , Pohjola V. , Sillanpää I.
Published: June 2010

Abstract. We study the solar wind induced oxygen ion escape from Venus' upper atmosphere and the Venus Express observations of the Venus-solar wind interaction by the HYB-Venus hybrid simulation code. We compare the simulation to the magnetic field and ion observations during an orbit of nominal upstream conditions. Further, we study the response of the induced magnetosphere to the emission of planetary ions. The hybrid simulation is found to be able to reproduce the main observed regions of the Venusian plasma environment: the bow shock (both perpendicular and parallel regions), the magnetic barrier, the central tail current sheet, the magnetic tail lobes, the magnetosheath and the planetary wake. The simulation is found to best fit the observations when the planetary \\oxy~escape rate is in the range from 3×1024 s−1 to 1.5×1025 s−1. This range was also found to be a limit for a test particle-like behaviour of the planetary ions: the higher escape rates manifest themselves in a different global configuration of the Venusian induced magnetosphere.
Polarization properties of Gendrin mode waves observed in the Earth's magnetosphere: observations and theory
Authors: Verkhoglyadova O. P. , Tsurutani B. T.
Published: June 2010

Abstract. We show a case of an outer zone magnetospheric electromagnetic wave propagating at the Gendrin angle, within uncertainty of the measurements. The chorus event occurred in a "minimum B pocket". For the illustrated example, the measured angle of wave propagation relative to the ambient magnetic field θkB was 58°±4°. For this event the theoretical Gendrin angle was 62°. Cold plasma model is used to demonstrate that Gendrin mode waves are right-hand circularly polarized, in excellent agreement with the observations.
3-D reconstructions of the early-November 2004 CDAW geomagnetic storms: analysis of Ooty IPS speed and density data
Authors: Bisi M. M. , Jackson B. V. , Clover J. M. , Manoharan P. K. , Tokumaru M. , Hick P. P. , Buffington A.
Published: June 2010

Abstract. Interplanetary scintillation (IPS) remote-sensing observations provide a view of the solar wind covering a wide range of heliographic latitudes and heliocentric distances from the Sun between ~0.1 AU and 3.0 AU. Such observations are used to study the development of solar coronal transients and the solar wind while propagating out through interplanetary space. They can also be used to measure the inner-heliospheric response to the passage of coronal mass ejections (CMEs) and co-rotating heliospheric structures. IPS observations can, in general, provide a speed estimate of the heliospheric material crossing the observing line of site; some radio antennas/arrays can also provide a radio scintillation level. We use a three-dimensional (3-D) reconstruction technique which obtains perspective views from outward-flowing solar wind and co-rotating structure as observed from Earth by iteratively fitting a kinematic solar wind model to these data. Using this 3-D modelling technique, we are able to reconstruct the velocity and density of CMEs as they travel through interplanetary space. For the time-dependent model used here with IPS data taken from the Ootacamund (Ooty) Radio Telescope (ORT) in India, the digital resolution of the tomography is 10° by 10° in both latitude and longitude with a half-day time cadence. Typically however, the resolutions range from 10° to 20° in latitude and longitude, with a half- to one-day time cadence for IPS data dependant upon how much data are used as input to the tomography. We compare reconstructed structures during early-November 2004 with in-situ measurements from the Wind spacecraft orbiting the Sun-Earth L1-Point to validate the 3-D tomographic reconstruction results and comment on how these improve upon prior reconstructions.
STEREO observations of interplanetary coronal mass ejections and prominence deflection during solar minimum period
Authors: Kilpua E. K. J. , Pomoell J. , Vourlidas A. , Vainio R. , Luhmann J. , Li Y. , Schroeder P. , Galvin A. B. , Simunac K.
Published: June 2010

Abstract. In this paper we study the occurrence rate and solar origin of interplanetary coronal mass ejections (ICMEs) using data from the two Solar TErrestrial RElation Observatory (STEREO) and the Wind spacecraft. We perform a statistical survey of ICMEs during the late declining phase of solar cycle 23. Observations by multiple, well-separated spacecraft show that even at the time of extremely weak solar activity a considerable number of ICMEs were present in the interplanetary medium. Soon after the beginning of the STEREO science mission in January 2007 the number of ICMEs declined to less than one ICME per month, but in late 2008 the ICME rate clearly increased at each spacecraft although no apparent increase in the number of coronal mass ejections (CMEs) occurred. We suggest that the near-ecliptic ICME rate can increase due to CMEs that have been guided towards the equator from their high-latitude source regions by the magnetic fields in the polar coronal holes. We consider two case studies to highlight the effects of the polar magnetic fields and CME deflection taking advantage of STEREO observations when the two spacecraft were in the quadrature configuration (i.e. separated by about 90 degrees). We study in detail the solar and interplanetary consequences of two CMEs that both originated from high-latitude source regions on 2 November 2008. The first CME was slow (radial speed 298 km/s) and associated with a huge polar crown prominence eruption. The CME was guided by polar coronal hole fields to the equator and it produced a clear flux rope ICME in the near-ecliptic solar wind. The second CME (radial speed 438 km/s) originated from an active region 11007 at latitude 35° N. This CME propagated clearly north of the first CME and no interplanetary consequences were identified. The two case studies suggest that slow and elongated CMEs have difficulties overcoming the straining effect of the overlying field and as a consequence they are guided by the polar coronal fields and cause in-situ effects close to the ecliptic plane. The 3-D propagation directions and CME widths obtained by using the forward modelling technique were consistent with the solar and in-situ observations.
Melting of major Glaciers in the western Himalayas: evidence of climatic changes from long term MSU derived tropospheric temperature trend (1979–2008)
Authors: Prasad A. K. , Yang K.-H. S. , El-Askary H. M. , Kafatos M.
Published: June 2010

Abstract. Global warming or the increase of the surface and atmospheric temperatures of the Earth, is increasingly discernible in the polar, sub-polar and major land glacial areas. The Himalayan and Tibetan Plateau Glaciers, which are the largest glaciers outside of the Polar Regions, are showing a large-scale decrease of snow cover and an extensive glacial retreat. These glaciers such as Siachen and Gangotri are a major water resource for Asia as they feed major rivers such as the Indus, Ganga and Brahmaputra. Due to scarcity of ground measuring stations, the long-term observations of atmospheric temperatures acquired from the Microwave Sounding Unit (MSU) since 1979–2008 is highly useful. The lower and middle tropospheric temperature trend based on 30 years of MSU data shows warming of the Northern Hemisphere's mid-latitude regions. The mean month-to-month warming (up to 0.048±0.026°K/year or 1.44°K over 30 years) of the mid troposphere (near surface over the high altitude Himalayas and Tibetan Plateau) is prominent and statistically significant at a 95% confidence interval. Though the mean annual warming trend over the Himalayas (0.016±0.005°K/year), and Tibetan Plateau (0.008±0.006°K/year) is positive, the month to month warming trend is higher (by 2–3 times, positive and significant) only over a period of six months (December to May). The factors responsible for the reversal of this trend from June to November are discussed here. The inequality in the magnitude of the warming trends of the troposphere between the western and eastern Himalayas and the IG (Indo-Gangetic) plains is attributed to the differences in increased aerosol loading (due to dust storms) over these regions. The monthly mean lower-tropospheric MSU-derived temperature trend over the IG plains (dust sink region; up to 0.032±0.027°K/year) and dust source regions (Sahara desert, Middle East, Arabian region, Afghanistan-Iran-Pakistan and Thar Desert regions; up to 0.068±0.033°K/year) also shows a similar pattern of month-to-month oscillation and six months of enhanced and a statistically significant warming trend. The enhanced warming trend during the winter and pre-monsoon months (December–May) may accelerate glacial melt. The unequal distribution of the warming trend over the year is discussed in this study and is partially attributed to a number of controlling factors such as sunlight duration, CO2 trends over the region (2003–2008), water vapor and aerosol distribution.