bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle precipitation during NEIAL events: simultaneous ground based nighttime observations at Svalbard
Authors: Lunde J. , Løvhaug U. P. , Gustavsson B.
Published: June 2010

Abstract. In this paper we present Naturally Enhanced Ion Acoustic Lines (NEIALs) observed with the EISCAT Svalbard Radar (ESR) together with auroral emissions observed with the Meridian Scanning Photometer (MSP). This is the first report of NEIALs observed during nighttime at Svalbard. Previously, NEIALs have been associated with a strong red line intensity (>10 kR), which exceeds the green line intensities. The high intensity in the red line emission is a sign of abundant low energy electron precipitation. In our observations, one of the NEIAL events was accompanied by the red line emissions far below the previously reported intensities. This happened when the green line intensity exceeds the red line intensity. In this work we discuss the behaviour of electron precipitation characteristics and optical emissions during NEIAL events on the nightside, and we suggest that intensity enhancements in the 844.6 nm emission line could be a better candidate than the 630.0 nm emission as an optical signature for NEIALs.
A recurrent neural network approach to quantitatively studying solar wind effects on TEC derived from GPS; preliminary results
Authors: Habarulema J. B. , McKinnell L.-A. , Opperman B. D. L.
Published: June 2010

Abstract. This paper attempts to describe the search for the parameter(s) to represent solar wind effects in Global Positioning System total electron content (GPS TEC) modelling using the technique of neural networks (NNs). A study is carried out by including solar wind velocity (Vsw), proton number density (Np) and the Bz component of the interplanetary magnetic field (IMF Bz) obtained from the Advanced Composition Explorer (ACE) satellite as separate inputs to the NN each along with day number of the year (DN), hour (HR), a 4-month running mean of the daily sunspot number (R4) and the running mean of the previous eight 3-hourly magnetic A index values (A8). Hourly GPS TEC values derived from a dual frequency receiver located at Sutherland (32.38° S, 20.81° E), South Africa for 8 years (2000–2007) have been used to train the Elman neural network (ENN) and the result has been used to predict TEC variations for a GPS station located at Cape Town (33.95° S, 18.47° E). Quantitative results indicate that each of the parameters considered may have some degree of influence on GPS TEC at certain periods although a decrease in prediction accuracy is also observed for some parameters for different days and seasons. It is also evident that there is still a difficulty in predicting TEC values during disturbed conditions. The improvements and degradation in prediction accuracies are both close to the benchmark values which lends weight to the belief that diurnal, seasonal, solar and magnetic variabilities may be the major determinants of TEC variability.
In-situ observation of ULF wave activities associated with substorm expansion phase onset and current disruption
Authors: Liang J. , Liu W. W. , Donovan E. F. , Spanswick E.
Published: June 2010

Abstract. In this paper we present two substorm events with coordinated ground-based and in-situ THEMIS observations, and focus our interest on the wave activities in Pi1 and Pi2 bands from minutes before the substorm expansion phase (EP) onset to minutes after the local current disruption (CD). We find that Pi2 band (40–100 s) wave appears 1–2 min before the substorm onset and last over the entire EP interval, while higher-frequency wave within Pi1 band (10–30 s) emerges within few tens of seconds after the EP onset, intensifies during the local CD, and fades afterwards. The pre-onset Pi2 waves are attributed to a ballooning mode which acts as the seed perturbation to the substorm EP onset process. The azimuthal wavenumber estimated from the Doppler shift nature of the ballooning mode is consistent with the longitudinal "wavelength" inferred from the onset auroral structures. The Pi1 waves appearing within few tens of seconds after the EP onset are interpreted as supportive of a two-fluid instability mode of thin current sheet investigated in an accompanying paper (Liu and Liang, 2009). During the local CD, broadband wave activities from Pi2 band to well above the ion gyrofrequency are observed, suggesting the coexistence of various plasma instabilities featuring different frequency ranges.
The structure of an earthward propagating magnetic flux rope early in its evolution: comparison of methods
Authors: Möstl C. , Farrugia C.J. , Biernat H. K. , Kiehas S. A. , Nakamura R. , Ivanova V. V. , Khotyaintsev Y.
Published: June 2010

Abstract. We analyze a magnetic signature associated with the leading edge of a bursty bulk flow observed by Cluster at −19 RE downtail on 22 August 2001. A distinct rotation of the magnetic field was seen by all four spacecraft. This event was previously examined by Slavin et al. (2003b) using both linear force-free modeling as well as a curlometer technique. Extending this work, we apply here single- and multi-spacecraft Grad-Shafranov (GS) reconstruction techniques to the Cluster observations and find good evidence that the structure encountered is indeed a magnetic flux rope and contains helical magnetic field lines. We find that the flux rope has a diameter of approximately 1 RE, an axial field of 26.4 nT, a velocity of ≈650 km/s, a total axial current of 0.16 MA and magnetic fluxes of order 105 Wb. The field line twist is estimated as half a turn per RE. The invariant axis is inclined at 40° to the ecliptic plane and 10° to the GSM equatorial plane. The flux rope has a force-free core and non-force-free boundaries. When we compare and contrast our results with those obtained from minimum variance, single-spacecraft force-free fitting and curlometer techniques, we find in general fair agreement, but also clear differences such as a higher inclination of the axis to the ecliptic. We further conclude that single-spacecraft methods have limitations which should be kept in mind when applied to THEMIS observations, and that non-force-free GS and curlometer techniques are to be preferred in their analysis. Some properties we derived for this earthward– moving structure are similar to those inferred by Lui et al. (2007), using a different approach, for a tailward-moving flux rope observed during the expansion phase of the same substorm.
Accuracy issues of the existing thermospheric wind models: can we rely on them in seeking solutions to wind-driven problems?
Authors: Larsen M. F. , Fesen C. G.
Published: June 2010

Abstract. We address the question of the ability of empirical and general circulation model neutral wind profiles in the lower thermosphere to reproduce the observed characteristics of the winds in that part of the atmosphere. The winds in that altitude range are critical for electrodynamic processes, but evaluations of the model winds are generally difficult because of the sparse observational data, which makes an evaluation of the wind predictions over large areas difficult or impossible. In this paper, we use a recently identified characteristic of the winds in the lower thermosphere, namely the enhanced winds and strong shears between 95 and 115 km altitude, as a test of the models, at least in a statistical sense. Our results show that the Horizontal Wind Model (HWM) significantly underestimates the maximum winds and shears in the lower thermosphere, although it has reasonable agreement with the average winds. The NCAR general circulation model used in this study also underestimates the maximum winds and shears significantly when run with standard resolution, as well as producing an unrealistic increase of the wind speed with height. The agreement between the model and the observations improves significantly however, in a statistical sense, when the altitude resolution is increased. The improved height resolution in the model appears to produce a greater improvement in the model predictions than any of the other factors that we examined, such as improving the geomagnetic forcing or the forcing at the lower boundary.
Estimation of electron densities in the lower thermosphere from GUVI 135.6 nm tomographic inversions in support of SpreadFEx
Authors: Kamalabadi F. , Comberiate J. M. , Taylor M. J. , Pautet P.-D.
Published: June 2010

Abstract. The SpreadFEx campaign was conducted with the goal of investigating potential neutral atmospheric dynamics influences in seeding plasma instabilities and bubbles extending to higher altitudes from September to November 2005, with primary measurements in Brazil. In this paper, we present the results of space-based UV and ground-based optical observations in support of this campaign. Specifically, we present multi-dimensional electron density images obtained tomographically from the 135.6 nm emissions measured by the GUVI instrument aboard the TIMED satellite that result from radiative recombination of O+ and compare those with the corresponding 630.0 nm OI images recorded in the Brazilian sector. The GUVI results provide altitude vs. longitude information on depleted regions in the ionospheric plasma density that are complementary to the single-height latitude-longitude images obtained with the airglow imager.
E-region decameter-scale plasma waves observed by the dual TIGER HF radars
Authors: Carter B. A. , Makarevich R. A.
Published: June 2010

Abstract. The dual Tasman International Geospace Environment Radar (TIGER) HF radars regularly observe E-region echoes at sub-auroral magnetic latitudes 58°–60° S including during geomagnetic storms. We present a statistical analysis of E-region backscatter observed in a period of ~2 years (late 2004–2006) by the TIGER Bruny Island and Unwin HF radars, with particular emphasis on storm-time backscatter. It is found that the HF echoes normally form a 300-km-wide band at ranges 225–540 km. In the evening sector during geomagnetic storms, however, the HF echoes form a curved band joining to the F-region band at ~700 km. The curved band lies close to the locations where the geometric aspect angle is zero, implying little to no refraction during geomagnetic storms, which is an opposite result to what has been reported in the past. The echo occurrence, Doppler velocity, and spectral width of the HF echoes are examined in order to determine whether new HF echo types are observed at sub-auroral latitudes, particularly during geomagnetic storms. The datasets of both TIGER radars are found to be dominated by low-velocity echoes. A separate population of storm-time echoes is also identified within the datasets of both radars with most of these echoes showing similar characteristics to the low-velocity echo population. The storm-time backscatter observed by the Bruny Island radar, on the other hand, includes near-range echoes (r<405 km) that exhibit some characteristics of what has been previously termed the High Aspect angle Irregularity Region (HAIR) echoes. We show that these echoes appear to be a storm-time phenomenon and further investigate this population by comparing their Doppler velocity with the simultaneously measured F- and E-region irregularity velocities. It is suggested that the HAIR-like echoes are observed only by HF radars with relatively poor geometric aspect angles when electron density is low and when the electric field is particularly high.
Comparing daytime, equatorial E×B drift velocities and TOPEX/TEC observations associated with the 4-cell, non-migrating tidal structure
Authors: Anderson D. , Araujo-Pradere E. , Scherliess L.
Published: June 2010

Abstract. We investigate the seasonal and longitude dependence of the daytime, vertical E×B drift velocities, on a day-to-day basis, using a recently-developed technique for inferring realistic E×B drifts from ground-based magnetometer observations. We have chosen only quiet days, Ap<10, from January 2001 through December 2002, so that the main contribution to the variability is due to the variability in the tidal forcing from below. In order to study the longitude dependence in daytime E×B drift velocities, we use appropriately-placed magnetometers in the Peruvian, Philippine, Indonesian and Indian longitude sectors. Since we are particularly interested in quantifying the E×B drift velocities associated with the 4-cell, non-migrating tidal structure, we compare the seasonal and longitude E×B drift structure with TOPEX satellite observations of Total Electron Content (TEC). We outline a plan to establish the magnitude of the longitude gradients that exist in the daytime, vertical E×B drift velocities at the boundaries of the observed 4-cell patterns and to theoretically identify the physical mechanisms that account for these sharp gradients. The paper demonstrates that sharp gradients in E×B drift velocities exist at one of the 4-cell boundaries and outlines how the C/NOFS IVM and VEFI sensor observations could be used to establish the E×B drift longitude gradients at the boundaries of each of the 4 cells. In addition, the paper identifies one of the theoretical, atmosphere/ionosphere models that could be employed to identify the physical mechanisms that might explain these observations.
Multi-spacecraft measurement of anisotropic power levels and scaling in solar wind turbulence
Authors: Osman K. T. , Horbury T. S.
Published: June 2010

Abstract. Measurements by the four Cluster spacecraft in the solar wind are used to determine quantitatively the field-aligned anisotropy of magnetohydrodynamic inertial range turbulence power levels and spectral indexes. We find, using time-lagged second order structure functions, that the spectral index is near 2 around the field-parallel direction, which is consistent with a "critical balance" turbulent cascade. Solar wind fluctuations are found to be anisotropic with power mainly in wavevectors perpendicular to the mean field, where the spectral index is around 5/3.
Global properties of magnetotail current sheet flapping: THEMIS perspectives
Authors: Runov A. , Angelopoulos V. , Sergeev V. A. , Glassmeier K.-H. , Auster U. , McFadden J. , Larson D. , Mann I.
Published: June 2010

Abstract. A sequence of magnetic field oscillations with an amplitude of up to 30 nT and a time scale of 30 min was detected by four of the five THEMIS spacecraft in the magnetotail plasma sheet. The probes P1 and P2 were at X=−15.2 and −12.7 RE and P3 and P4 were at X=−7.9 RE. All four probes were at −6.5>Y>−7.5 RE (major conjunction). Multi-point timing analysis of the magnetic field variations shows that fronts of the oscillations propagated flankward (dawnward and Earthward) nearly perpendicular to the direction of the magnetic maximum variation (B1) at velocities of 20–30 km/s. These are typical characteristics of current sheet flapping motion. The observed anti-correlation between ∂B1/∂t and the Z-component of the bulk velocity make it possible to estimate a flapping amplitude of 1 to 3 RE. The cross-tail scale wave-length was found to be about 5 RE. Thus the flapping waves are steep tail-aligned structures with a lengthwise scale of >10 RE. The intermittent plasma motion with the cross-tail velocity component changing its sign, observed during flapping, indicates that the flapping waves were propagating through the ambient plasma. Simultaneous observations of the magnetic field variations by THEMIS ground-based magnetometers show that the flapping oscillations were observed during the growth phase of a substorm.
4-D modeling of CME expansion and EUV dimming observed with STEREO/EUVI
Authors: Aschwanden M. J.
Published: June 2010

Abstract. This is the first attempt to model the kinematics of a CME launch and the resulting EUV dimming quantitatively with a self-consistent model. Our 4-D-model assumes self-similar expansion of a spherical CME geometry that consists of a CME front with density compression and a cavity with density rarefaction, satisfying mass conservation of the total CME and swept-up corona. The model contains 14 free parameters and is fitted to the 25 March 2008 CME event observed with STEREO/A and B. Our model is able to reproduce the observed CME expansion and related EUV dimming during the initial phase from 18:30 UT to 19:00 UT. The CME kinematics can be characterized by a constant acceleration (i.e., a constant magnetic driving force). While the observations of EUVI/A are consistent with a spherical bubble geometry, we detect significant asymmetries and density inhomogeneities with EUVI/B. This new forward-modeling method demonstrates how the observed EUV dimming can be used to model physical parameters of the CME source region, the CME geometry, and CME kinematics.
First simultaneous measurements of waves generated at the bow shock in the solar wind, the magnetosphere and on the ground
Authors: Clausen L. B. N. , Yeoman T. K. , Fear R. C. , Behlke R. , Lucek E. A. , Engebretson M. J.
Published: June 2010

Abstract. On 5 September 2002 the Geotail satellite observed the cone angle of the Interplanetary Magnetic Field (IMF) change to values below 30° during a 56 min interval between 18:14 and 19:10 UT. This triggered the generation of upstream waves at the bow shock, 13 RE downstream of the position of Geotail. Upstream generated waves were subsequently observed by Geotail between 18:30 and 18:48 UT, during times the IMF cone angle dropped below values of 10°. At 18:24 UT all four Cluster satellites simultaneously observed a sudden increase in wave power in all three magnetic field components, independent of their position in the dayside magnetosphere. We show that the 10 min delay between the change in IMF direction as observed by Geotail and the increase in wave power observed by Cluster is consistent with the propagation of the IMF change from the Geotail position to the bow shock and the propagation of the generated waves through the bow shock, magnetosheath and magnetosphere towards the position of the Cluster satellites. We go on to show that the wave power recorded by the Cluster satellites in the component containing the poloidal and compressional pulsations was broadband and unstructured; the power in the component containing toroidal oscillations was structured and shows the existence of multi-harmonic Alfvénic continuum waves on field lines. Model predictions of these frequencies fit well with the observations. An increase in wave power associated with the change in IMF direction was also registered by ground based magnetometers which were magnetically conjunct with the Cluster satellites during the event. To the best of our knowledge we present the first simultaneous observations of waves created by backstreaming ions at the bow shock in the solar wind, the dayside magnetosphere and on the ground.
Transient teleconnection event at the onset of a planet-encircling dust storm on Mars
Authors: Martínez-Alvarado O. , Montabone L. , Lewis S. R. , Moroz I. M. , Read P. L.
Published: June 2010

Abstract. We use proper orthogonal decomposition (POD) to study a transient teleconnection event at the onset of the 2001 planet-encircling dust storm on Mars, in terms of empirical orthogonal functions (EOFs). There are several differences between this and previous studies of atmospheric events using EOFs. First, instead of using a single variable such as surface pressure or geopotential height on a given pressure surface, we use a dataset describing the evolution in time of global and fully three-dimensional atmospheric fields such as horizontal velocity and temperature. These fields are produced by assimilating Thermal Emission Spectrometer observations from NASA's Mars Global Surveyor spacecraft into a Mars general circulation model. We use total atmospheric energy (TE) as a physically meaningful quantity which weights the state variables. Second, instead of adopting the EOFs to define teleconnection patterns as planetary-scale correlations that explain a large portion of long time-scale variability, we use EOFs to understand transient processes due to localised heating perturbations that have implications for the atmospheric circulation over distant regions. The localised perturbation is given by anomalous heating due to the enhanced presence of dust around the northern edge of the Hellas Planitia basin on Mars. We show that the localised disturbance is seemingly restricted to a small number (a few tens) of EOFs. These can be classified as low-order, transitional, or high-order EOFs according to the TE amount they explain throughout the event. Despite the global character of the EOFs, they show the capability of accounting for the localised effects of the perturbation via the presence of specific centres of action. We finally discuss possible applications for the study of terrestrial phenomena with similar characteristics.
In situ observations from STEREO/PLASTIC: a test for L5 space weather monitors
Authors: Simunac K. D. C. , Kistler L. M. , Galvin A. B. , Popecki M. A. , Farrugia C. J.
Published: June 2010

Abstract. Stream interaction regions (SIRs) that corotate with the Sun (corotating interaction regions, or CIRs) are known to cause recurrent geomagnetic storms. The Earth's L5 Lagrange point, separated from the Earth by 60 degrees in heliographic longitude, is a logical location for a solar wind monitor – nearly all SIRs/CIRs will be observed at L5 several days prior to their arrival at Earth. Because the Sun's heliographic equator is tilted about 7 degrees with respect to the ecliptic plane, the separation in heliographic latitude between L5 and Earth can be more than 5 degrees. In July 2008, during the period of minimal solar activity at the end of solar cycle 23, the two STEREO observatories were separated by about 60 degrees in longitude and more than 4 degrees in heliographic latitude. This time period affords a timely test for the practical application of a solar wind monitor at L5. We compare in situ observations from PLASTIC/AHEAD and PLASTIC/BEHIND, and report on how well the BEHIND data can be used as a forecasting tool for in situ conditions at the AHEAD spacecraft with the assumptions of ideal corotation and minimal source evolution. Preliminary results show the bulk proton parameters (density and bulk speed) are not in quantitative agreement from one observatory to the next, but the qualitative profiles are similar.
Field-aligned structure of poloidal Alfvén waves in a finite pressure plasma
Authors: Mager P. N. , Klimushkin D. Yu. , Pilipenko V. A. , Schäfer S.
Published: June 2010

Abstract. This paper is devoted to analytical and numerical studies of the parallel structure of poloidal Alfvén waves in a finite pressure plasma. The effects of finite-beta plasma are especially essential near the magnetospheric equator, where an opaque (non-transparent) region for Alfvén waves can be formed. This region is bounded by two turning points which restrain penetration of the wave energy far from the ionosphere, and an Alfvén resonator appears on a part of the field line adjacent to the ionosphere. Due to this effect the ULF pulsations in the Northern and Southern Hemispheres can be non-conjugated. Another result is a peculiar field-aligned structure of the wave magnetic field: its fundamental harmonic must have three nodes, rather than one node as is the case in cold plasma.
Modulation of nightside polar patches by substorm activity
Authors: Wood A. G. , Pryse S. E. , Moen J.
Published: June 2010

Abstract. Results are presented from a multi-instrument study showing the influence of geomagnetic substorm activity on the spatial distribution of the high-latitude ionospheric plasma. Incoherent scatter radar and radio tomography measurements on 12 December 2001 were used to directly observe the remnants of polar patches in the nightside ionosphere and to investigate their characteristics. The patches occurred under conditions of IMF Bz negative and IMF By negative. They were attributed to dayside photoionisation transported by the high-latitude convection pattern across the polar cap and into the nighttime European sector. The patches on the nightside were separated by some 5° latitude during substorm expansion, but this was reduced to some 2° when the activity had subsided. The different patch separations resulted from the expansion and contraction of the high-latitude plasma convection pattern on the nightside in response to the substorm activity. The patches of larger separation occurred in the antisunward cross-polar flow as it entered the nightside sector. Those of smaller separation were also in antisunward flow, but close to the equatorward edge of the convection pattern, in the slower, diverging flow at the Harang discontinuity. A patch repetition time of some 10 to 30 min was estimated depending on the phase of the substorm.
Fibre structure of decametric type II radio bursts as a manifestation of emission propagation effects in a disturbed near-solar plasma
Authors: Afanasiev A. N.
Published: June 2010

Abstract. This paper addresses the fine structure of solar decametric type II radio bursts in the form of drifting narrowband fibres on the dynamic spectrum. Observations show that this structure appears in those events where there is a coronal mass ejection (CME) traveling in the near-solar space ahead of the shock wave responsible for the radio burst. The diversity in observed morphology of fibres and values of their parameters implies that the fibres may be caused by different formation mechanisms. The burst emission propagates through extremely inhomogeneous plasma of the CME, so one possible mechanism can be related to radio propagation effects. I suggest that the fibres in some events represent traces of radio emission caustics, which are formed due to regular refraction of radio waves on the large-scale inhomogeneous structure of the CME front. To support this hypothesis, I have modeled the propagation of radio waves through inhomogeneous plasma of the CME, taking into consideration the presence of electron density fluctuations in it. The calculations, which are based on the Monte Carlo technique, indicate that, in particular, the emission of the fibres should be harmonic. Moreover, the mechanism under consideration suggests that in solar observations from two different points in space, the observed sets of fibres can be shifted in frequency with respect to one another or can have a different structure. This potentially can be used for identifying fibres caused by the propagation effects.
A route to explosive large-scale magnetic reconnection in a super-ion-scale current sheet
Authors: Tanaka K. G. , Haijima K. , Fujimoto M. , Shinohara I.
Published: June 2010

Abstract. How to trigger magnetic reconnection is one of the most interesting and important problems in space plasma physics. Recently, electron temperature anisotropy (αeo=Te⊥/Te||) at the center of a current sheet and non-local effect of the lower-hybrid drift instability (LHDI) that develops at the current sheet edges have attracted attention in this context. In addition to these effects, here we also study the effects of ion temperature anisotropy (αio=Ti⊥/Ti||). Electron anisotropy effects are known to be helpless in a current sheet whose thickness is of ion-scale. In this range of current sheet thickness, the LHDI effects are shown to weaken substantially with a small increase in thickness and the obtained saturation level is too low for a large-scale reconnection to be achieved. Then we investigate whether introduction of electron and ion temperature anisotropies in the initial stage would couple with the LHDI effects to revive quick triggering of large-scale reconnection in a super-ion-scale current sheet. The results are as follows. (1) The initial electron temperature anisotropy is consumed very quickly when a number of minuscule magnetic islands (each lateral length is 1.5~3 times the ion inertial length) form. These minuscule islands do not coalesce into a large-scale island to enable large-scale reconnection. (2) The subsequent LHDI effects disturb the current sheet filled with the small islands. This makes the triggering time scale to be accelerated substantially but does not enhance the saturation level of reconnected flux. (3) When the ion temperature anisotropy is added, it survives through the small island formation stage and makes even quicker triggering to happen when the LHDI effects set-in. Furthermore the saturation level is seen to be elevated by a factor of ~2 and large-scale reconnection is achieved only in this case. Comparison with two-dimensional simulations that exclude the LHDI effects confirms that the saturation level enhancement is due to the ion anisotropy effects, while the LHDI effects shorten the overall time scale significantly. The results imply that the ion temperature anisotropy is one of the key properties that enable large-scale magnetic reconnection to develop in a super-ion-scale current sheet.
Scale size and life time of energy conversion regions observed by Cluster in the plasma sheet
Authors: Hamrin M. , Norqvist P. , Marghitu O. , Vaivads A. , Klecker B. , Kistler L. M. , Dandouras I.
Published: June 2010

Abstract. In this article, and in a companion paper by Hamrin et al. (2009) [Occurrence and location of concentrated load and generator regions observed by Cluster in the plasma sheet], we investigate localized energy conversion regions (ECRs) in Earth's plasma sheet. From more than 80 Cluster plasma sheet crossings (660 h data) at the altitude of about 15–20 RE in the summer and fall of 2001, we have identified 116 Concentrated Load Regions (CLRs) and 35 Concentrated Generator Regions (CGRs). By examining variations in the power density, E·J, where E is the electric field and J is the current density obtained by Cluster, we have estimated typical values of the scale size and life time of the CLRs and the CGRs. We find that a majority of the observed ECRs are rather stationary in space, but varying in time. Assuming that the ECRs are cylindrically shaped and equal in size, we conclude that the typical scale size of the ECRs is 2 RE≲ΔSECR≲5 RE. The ECRs hence occupy a significant portion of the mid altitude plasma sheet. Moreover, the CLRs appear to be somewhat larger than the CGRs. The life time of the ECRs are of the order of 1–10 min, consistent with the large scale magnetotail MHD simulations of Birn and Hesse (2005). The life time of the CGRs is somewhat shorter than for the CLRs. On time scales of 1–10 min, we believe that ECRs rise and vanish in significant regions of the plasma sheet, possibly oscillating between load and generator character. It is probable that at least some of the observed ECRs oscillate energy back and forth in the plasma sheet instead of channeling it to the ionosphere.
Inferring hydroxyl layer peak heights from ground-based measurements of OH(6-2) band integrated emission rate at Longyearbyen (78° N, 16° E)
Authors: Mulligan F. J. , Dyrland M. E. , Sigernes F. , Deehr C. S.
Published: June 2010

Abstract. Measurements of hydroxyl nightglow emissions over Longyearbyen (78° N, 16° E) recorded simultaneously by the SABER instrument onboard the TIMED satellite and a ground-based Ebert-Fastie spectrometer have been used to derive an empirical formula for the height of the OH layer as a function of the integrated emission rate (IER). Altitude profiles of the OH volume emission rate (VER) derived from SABER observations over a period of more than six years provided a relation between the height of the OH layer peak and the integrated emission rate following the procedure described by Liu and Shepherd (2006). An extended period of overlap of SABER and ground-based spectrometer measurements of OH(6-2) IER during the 2003–2004 winter season allowed us to express ground-based IER values in terms of their satellite equivalents. The combination of these two formulae provided a method for inferring an altitude of the OH emission layer over Longyearbyen from ground-based measurements alone. Such a method is required when SABER is in a southward looking yaw cycle. In the SABER data for the period 2002–2008, the peak altitude of the OH layer ranged from a minimum near 76 km to a maximum near 90 km. The uncertainty in the inferred altitude of the peak emission, which includes a contribution for atmospheric extinction, was estimated to be ±2.7 km and is comparable with the ±2.6 km value quoted for the nominal altitude (87 km) of the OH layer. Longer periods of overlap of satellite and ground-based measurements together with simultaneous on-site measurements of atmospheric extinction could reduce the uncertainty to approximately 2 km.
Modelling of mirror mode structures as propagating slow magnetosonic solitons
Authors: Stasiewicz K. , Cheng C. Z.
Published: June 2010

Abstract. Cluster measurements in the magnetosheath with spacecraft separations of 2000 km indicate that magnetic pulsations interpreted as mirror mode structures are not frozen in plasma flow, but do propagate with speeds of up to ~50 km/s. Properties of these pulsations are shown to be consistent with propagating slow magnetosonic solitons. By using nonlinear two fluid theory we demonstrate that the well known classical mirror instability condition corresponds to a small subset in a continuum of exponentially varying solutions. With the measured plasma moments we have determined parameters of the polybaric pressure model in the region of occurrence of mirror type structures and applied it to numerical modelling of these structures. In individual cases we obtain excellent agreement between observed mirror mode structures and numerical solutions for magnetosonic solitons.
Fine structures and dynamics in auroral initial brightening at substorm onsets
Authors: Sakaguchi K. , Shiokawa K. , Ieda A. , Nomura R. , Nakajima A. , Greffen M. , Donovan E. , Mann I. R. , Kim H. , Lessard M.
Published: June 2010

Abstract. We show four auroral initial brightening events at substorm onsets focusing on fine structures and their longitudinal dynamics, which were observed by all-sky TV cameras (30-Hz sampling) on January 2008, in Canada. For two initial brightenings started in the field of views of the cameras, we found that they started at longitudinal segments with a size of less than ~30–60 km. One brightening expanded with wavy structures and the other expanded as a straight arc. Although the two events had different structures, both brightening auroras expanded with an average speed of ~20 km/s in the first 10 s, and ~10 km/s in the following 10 s. The other two events show that brightening auroras developed with periodic structures, with longitudinal wavelengths of ~100–200 km. Assuming that the brightening auroras are mapped to the physical processes occurring in the plasma sheet, we found that the scale size (30–60 km) and the expanding speed (20 km/s) of brightening auroras correspond to the order of ion gyro radii (~500–1400 km) and Alfvén speed or fast ion-flow speed (~400 km/s), respectively, in the plasma sheet.
Observational evidences on the modulation of the South American Low Level Jet east of the Andes according the ENSO variability
Authors: Silva G. A. M. , Ambrizzi T. , Marengo J. A.
Published: June 2010

Abstract. The differences on the phase and wavelength of the quasi-stationary waves over the South America generated by El Niño (EN) and La Niña (LN) events seem to affect the daily evolution of the South American Low Level Jet east of the Andes (SALLJ). For the austral summer period of 1977–2004 the SALLJ episodes detected according to Bonner criterion 1 show normal to above-normal frequency in EN years, and in LN years the episodes show normal to below-normal frequency. During EN and LN years the SALLJ episodes were associated with positive rainfall anomalies over the La Plata Basin, but more intense during LN years. During EN years the increase in the SALLJ cases were associated to intensification of the Subtropical Jet (SJ) around 30° S and positive Sea Level Pressure (SLP) anomalies over the western equatorial Atlantic and tropical South America, particularly over central Brazil. This favored the intensification of the northeasterly trade winds over the northern continent and it channeled by the Andes mountain to the La Plata Basin region where negative SLP are found. The SALLJ cases identified during the LN events were weaker and less frequent when compared to those for EN years. In this case the SJ was weaker than in EN years and the negative SLP anomalies over the tropical continent contributed to the inversion of the northeasterly trade winds. Also a southerly flow anomaly was generated by the geostrophic balance due to the anomalous blocking over southeast Pacific and the intense cyclonic transient over the southern tip of South America. As result the warm tropical air brought by the SALLJ encounters the cold extratropical air from the southerly winds over the La Plata basin. This configuration can increase the conditional instability over the La Plata basin and may explain the more intense positive rainfall anomalies in SALLJ cases during LN years than in EN years.
Low frequency eigenmodes of thin anisotropic current sheets and Cluster observations
Authors: Zelenyi L. M. , Artemyev A. V. , Petrukovich A. A. , Nakamura R. , Malova H. V. , Popov V. Y.
Published: June 2010

Abstract. The eigenmodes of low frequency perturbations of thin anisotropic current sheets with a finite value of the normal magnetic field, are investigated in this paper. It is shown that two possible polarizations of symmetric and asymmetric modes (sausage and kink) exist where the growth rate of instabilities is positive. In addition, we demonstrate that a tearing instability might have a positive growth rate in thin anisotropic current sheets. The class of relatively fast wavy flapping oscillations observed by Cluster is described. The main direction of wave motion coincides with the direction of the current and the typical velocity of this motion is comparable with the plasma drift velocity in the current sheet. The comparison of these characteristics with theoretical predictions of the model of anisotropic thin current sheets, demonstrates that, in principle, the theory adequately describes the observations.
Electrojet control of ambient ionization near the crest of the equatorial anomaly in the Indian zone
Authors: Chakraborty S. K. , Hajra R.
Published: June 2010

Abstract. A long-term (1978–1990) database of total electron content (TEC) from a location (Calcutta: 22.58° N, 88.38° E geographic, dip: 32° N) near the northern crest of the equatorial ionization anomaly has extensively been studied to characterize the contribution of fountain effect in the maintenance of ambient ionization. The equatorial electrojet (EEJ) data obtained from ground magnetometer recording are used to assess the contribution of equatorial fountain. Analysis made with instantaneous values, day's maximum values and time-integrated values of EEJ strength exhibit more or less similar features. When instantaneous values of EEJ are considered TEC variations exhibit two maxima in correlation, one around 10:00–12:00 IST and the other around 18:00–20:00 IST. The later maximum in correlation coefficient is conspicuously absent when integrated values of EEJ are considered. An impulse-like feature is reflected in the diurnal TEC variation during the time intervals (09:00–10:00 IST) and (18:00–19:00 IST). The statistical analysis reveals greater correspondence with high level of significance between diurnal TEC and EEJ in the descending epoch of solar cycle than in the ascending one. On the seasonal basis, TEC in the summer solstitial months are observed to be more sensitive to the changes in EEJ strength than in the equinoctial and winter solstitial months. Combining the effects of solar flux, season, local time and EEJ an empirical formula for monthly mean diurnal TEC has been developed and validated using observed TEC data. An estimation of the relative contributions of the several terms appearing in the formula reveals much more solar flux contribution (~50–70%) in the maintenance of ambient ionization around the present location than the EEJ effects (maximum~20%).
On the 3-D reconstruction of Coronal Mass Ejections using coronagraph data
Authors: Mierla M. , Inhester B. , Antunes A. , Boursier Y. , Byrne J. P. , Colaninno R. , Davila J. , de Koning C. A. , Gallagher P. T. , Gissot S. , Howard R. A. , Howard T. A. , Kramar M. , Lamy P. , Liewer P. C. , Maloney S. , Marqué C. , McAteer R. T. J. , Moran T. , Rodriguez L. , Srivastava N. , Cyr O. C. St. , Stenborg G. , Temmer M. , Thernisien A. , Vourlidas A. , West M. J. , Wood B. E. , Zhukov A. N.
Published: June 2010

Abstract. Coronal Mass ejections (CMEs) are enormous eruptions of magnetized plasma expelled from the Sun into the interplanetary space, over the course of hours to days. They can create major disturbances in the interplanetary medium and trigger severe magnetic storms when they collide with the Earth's magnetosphere. It is important to know their real speed, propagation direction and 3-D configuration in order to accurately predict their arrival time at the Earth. Using data from the SECCHI coronagraphs onboard the STEREO mission, which was launched in October 2006, we can infer the propagation direction and the 3-D structure of such events. In this review, we first describe different techniques that were used to model the 3-D configuration of CMEs in the coronagraph field of view (up to 15 R⊙). Then, we apply these techniques to different CMEs observed by various coronagraphs. A comparison of results obtained from the application of different reconstruction algorithms is presented and discussed.
Statistics of counter-streaming solar wind suprathermal electrons at solar minimum: STEREO observations
Authors: Lavraud B. , Opitz A. , Gosling J. T. , Rouillard A. P. , Meziane K. , Sauvaud J.-A. , Fedorov A. , Dandouras I. , Génot V. , Jacquey C. , Louarn P. , Mazelle C. , Penou E. , Larson D. E. , Luhmann J. G. , Schroeder P. , Jian L. , Russell C. T. , Foullon C. , Skoug R. M. , Steinberg J. T. , Simunac K. D. , Galvin A. B.
Published: June 2010

Abstract. Previous work has shown that solar wind suprathermal electrons can display a number of features in terms of their anisotropy. Of importance is the occurrence of counter-streaming electron patterns, i.e., with "beams" both parallel and anti-parallel to the local magnetic field, which is believed to shed light on the heliospheric magnetic field topology. In the present study, we use STEREO data to obtain the statistical properties of counter-streaming suprathermal electrons (CSEs) in the vicinity of corotating interaction regions (CIRs) during the period March–December 2007. Because this period corresponds to a minimum of solar activity, the results are unrelated to the sampling of large-scale coronal mass ejections, which can lead to CSE owing to their closed magnetic field topology. The present study statistically confirms that CSEs are primarily the result of suprathermal electron leakage from the compressed CIR into the upstream regions with the combined occurrence of halo depletion at 90° pitch angle. The occurrence rate of CSE is found to be about 15–20% on average during the period analyzed (depending on the criteria used), but superposed epoch analysis demonstrates that CSEs are preferentially observed both before and after the passage of the stream interface (with peak occurrence rate >35% in the trailing high speed stream), as well as both inside and outside CIRs. The results quantitatively show that CSEs are common in the solar wind during solar minimum, but yet they suggest that such distributions would be much more common if pitch angle scattering were absent. We further argue that (1) the formation of shocks contributes to the occurrence of enhanced counter-streaming sunward-directed fluxes, but does not appear to be a necessary condition, and (2) that the presence of small-scale transients with closed-field topologies likely also contributes to the occurrence of counter-streaming patterns, but only in the slow solar wind prior to CIRs.
The influence of Titan on Saturn kilometric radiation
Authors: Menietti J. D. , Ye S.-Y. , Piker C. W. , Cecconi B.
Published: June 2010

Abstract. Previous studies have shown that the occurrence probability of Saturn Kilometric Radiation (SKR) appears to be influenced by the local time of Titan. Using a more extensive set of data than the original study, we confirm the correlation of higher occurrence probability of SKR when Titan is located near local midnight. In addition, the direction finding capability of the Cassini Radio Plasma Wave instrument (RPWS) is used to determine if this radio emission emanates from particular source regions. We find that most source regions of SKR are located in the mid-morning sector of local time even when Titan is located near midnight. However, some emission does appear to have a source in the Saturnian nightside, consistent with electron precipitation from field lines that have recently mapped to near Titan.
Analysis of gravity-waves produced by intense tropical cyclones
Authors: Chane Ming F. , Chen Z. , Roux F.
Published: June 2010

Abstract. Conventional and wavelet methods are combined to characterize gravity-waves (GWs) produced by two intense tropical cyclones (TCs) in the upper troposphere and lower stratosphere (UT/LS) from GPS winsonde data. Analyses reveal large contribution of GWs induced by TCs to wave energy densities in the UT/LS. An increase in total energy density of about 30% of the climatological energy density in austral summer was estimated in the LS above Tromelin during TC Dina. Four distinct periods in GW activity in relation with TC Faxai stages is observed in the UT. Globally, GWs have periods of 6 h–2.5 days, vertical wavelenghts of 1–3 km and horizontal wavelengths <1000 km in the UT during the evolution of TCs. Horizontal wavelengths are longer in the LS and about 2200 km during TCs. Convective activity over the basin and GW energy density were modulated by mixed equatorial waves of 3–4 days, 6–8 days and 10–13 days confirmed by Hövmöller diagram, Fourier and wavelet analyses of OLR data. Moreover, location of GW sources is below the tropopause height when TCs are intense otherwise varies at lower tropospheric heights depending on the strength of convection. Finally, the maximum surface wind speeds of TCs Dina and Faxai can be linearly estimated with total energy densities.
Low altitude energetic electron lifetimes after enhanced magnetic activity as deduced from SAC-C and DEMETER data
Authors: Benck S. , Mazzino L. , Cyamukungu M. , Cabrera J. , Pierrard V.
Published: June 2010

Abstract. When flux enhancements of energetic electrons are produced as a consequence of geomagnetic storm occurrence, they tend to vanish gradually when the magnetic activity calms down and the fluxes decay to quiet-time levels. We use SAC-C and DEMETER low altitude observations to estimate the energetic electron lifetimes (E=0.16–1.4 MeV, L=1.6–5, B=0.22–0.46 G) and compare the decay rates to those observed at high altitude. While crossing the radiation belts at high latitude, the SAC-C and DEMETER instruments sample particles with small equatorial pitch angles (αeq<18° for L>2.5) whereas the comparison is done with other satellite data measured mainly in the equatorial plane (for αeq>75°). While in the inner belt and in the slot region no significant lifetime differences are observed from the data sets with different αeq, in the outer belt, for the least energetic electrons (<500 keV), the lifetimes are up to ~3 times larger for the electrons with the equatorial pitch-angle close to the loss cone than for those mirroring near the equator. The difference decreases with increasing energy and vanishes for energies of about 1 MeV.