SA21A-0264
Evolution of the Detached Westward Flow Channel as Observed by the Unwin HF Radar
We examine the spatial and temporal evolution of latitudinally narrow regions with enhanced Doppler velocity observed by the Unwin TIGER HF radar equatorward of Auroral Westward Flow Channels. AWFCs were detected by both the Bruny Island and New Zealand (Unwin) TIGER radars as regions with enhanced westward convection, at about -62 deg MLAT. A second, more equatorward (~ -60 deg MLAT) channel with enhanced westward convection was detected only by the Unwin radar. The spatio-temporal behaviour of the second channel and its characteristics were found to be significantly different from those of AWFCs, e.g. both the channel and flow directions were significantly non-L-shell-aligned. We also investigate the relationship between the flow speeds within the two types of flow channels. In all cases, the second channel appeared to originate within or close to the AWFC, with the flow deviation from the magnetic L-shell direction and latitudinal separation between channels increasing with time. In sharp contrast to the AWFC that persisted for 2-3 hours, the second channel was recognizable only for 30-50 min. A relation between multiple flow channels and other subauroral phenomena such as subauroral ion drifts (SAID) and subauroral polarization streams (SAPS), and the implications of observations for models of SAID and SAPS formation are discussed.
SA21A-0265
Initial Observations of Storm-Time and Disturbance Electric Fields in the Subauroral and Mid-Latitude Ionospheres Using the SuperDARN-Storm Radar at Wallops Island, VA
In May of 2005, the Johns Hopkins University Applied Physics Laboratory in collaboration with the Goddard Space Flight Center Wallops Flight Facility began operation of a new SuperDARN radar located near the Wallops Island sounding rocket launch site. The radar is the first of the SuperDARN network that has been sited at a mid-latitude location from which it can detect electron density irregularities produced by ionospheric electric fields and density gradients during disturbed geomagnetic conditions with particular emphasis on geomagnetic storms. The radar scans over a 52 degree azimuth sector that extends over much of the North Atlantic Ocean and has spatial and temporal resolutions of ~50 km and 1-2 minutes. Doppler information from the backscattered signals is used to determine the spatial structure and temporal variability of electric fields and plasma convection in the low-latitude portion of the auroral, subauroral and mid-latitude ionospheres. Since the radar began operations, there have been significant geomagnetic storms on May 15th, June 12th, June 23rd, August 24th, and August 31st of the present year. There have also been a number of other days that have displayed strong non-storm disturbances. Using these events we have been able to identify storm-enhanced convection electric fields at all local times and a broad range of latitudes extending from 50-70 degrees geomagnetic. In this paper, we present examples of penetrating electric fields at a number of local times as well as midnight sector subauroral flow enhancements that are very similar to the SAID events observed with low-altitude spacecraft. One of the unique aspects of the later phenomena is that the Wallops radar allows us to observe the growth and decay of SAID-type flows.
SA21A-0266
A Survey of the Storm-Time Ionospheric Scatter Seen by the Mid-Latitude SuperDARN Wallops Island Radar
We present a survey of the ionospheric backscatter from the SuperDARN Wallops Island radar versus magnetic latitude and local time. Since the radar came into operation in early May 2005 it has made frequent observations of disturbed and storm time electric fields and plasma motions at magnetic latitudes of 50-70 degrees. On occasion, the radar observes enhanced flows for several hours in similar local time sectors for several consecutive days. We show several examples of penetration electric fields and discuss the importance of these lower-latitude convection measurements in the determination of the total cross polar cap potential. Without data from mid-latitudes, the SuperDARN polar cap potential may be significantly underestimated during disturbed conditions and geomagnetic storms. We also present initial results from our efforts to develop an observational model of mid-latitude storm-time convection. This will be the first step in developing an observational model of the spatial and temporal evolution of inner magnetosphere electric fields during storm-time conditions.
SA21A-0267
Low-latitude Ionosphere-Thermosphere Response to Electric Fields During Magnetic Storms
The low-latitude and equatorial ionosphere dynamics is mostly controlled by electric fields. During disturbed periods, magnetospheric electric fields can penetrate into the low-latitude and equatorial ionosphere as a consequence of rapid changes in magnetospheric convection. On the other hand, the dynamo action of thermospheric winds driven by storm heating at high latitudes modifies the electric field characteristic of quiet periods at those latitudes. In this work, ionosonde, magnetometer and satellite observations, as well as the global, three-dimensional, time-dependent, non-linear coupled model of the thermosphere, ionosphere, plasmasphere and electrodynamics (CTIPe) are used to analyse both prompt penetration and disturbance dynamo electric field effects on low-latitude ionosphere during periods of intense magnetic activity.
SA21A-0268
Unusual topside ionospheric density response to the November 2003 superstorm
We use observations from a variety of different ground and space-based instruments, including ionosonde, ground and space-based Global Positioning System (GPS) receivers, magnetometers, and the solar wind data from the Advanced Composition Explorer (ACE), to examine the response of the ionospheric F2-layer height during the November 2003 superstorm. We found that the topside ionosphere responded unusually to the November 20, 2003 severe storm. While ground-based GPS receivers observed a large enhancement in dayside TEC, the Low-Earth orbiting (~400 km) CHAMP satellite did not show any sign of dayside TEC enhancement. The real-time vertical density profiles, constructed from ground based GPS TEC using a tomographic reconstruction technique, clearly revealed that the ionospheric F2-layer peak height had been depressed down to lower altitudes. Ionospheric F-layer peak height (hmF2) from the nearby ionosonde stations over Europe also showed that the dayside F2-layer peak height was below 350 km, which is below the orbiting height of CHAMP, on 20 November 2003. The vertical E x B drift (estimated from ground-based magnetometer equatorial electrojet delta H) did show dayside strong downward drifts, which may be attributed to the ionospheric disturbance dynamo electric field produced by the large amount of energy dissipation into high latitude regions. This storm demonstrates that care has to be taken in interpreting data from LEO satellites.
SA21A-0269
The Longitudinal Dependence of the Mid-Latitude ionospheric Effect of Large Geomagnetic Storms
In recent years much attention has been given to the effect of large geomagnetic storms over the region of the USA. Enhancements of TEC by a factor of two or more have been reported, and, of very special interest from the GPS point of view, very steep ionospheric density gradients have been reported in the American sector. A survey of recent literature on this subject leaves one to wonder whether these storm effects are confined to the longitudes of the North American continent, or whether such effects might be present around the globe. We address this question with both a modeling approach and a systematic analysis of ionosonde data from the last 20 years. In our analysis of the observations we look for the presence or absence of four specific characteristics: a dusk effect, a positive storm phase, a negative storm phase, and a steep density gradient. We have previously reported on our success in modeling the TEC enhancements and high density gradients in the American sector by introducing a penetrating electric field that induces an upward vertical drift in the dayside mid-latitude ionosphere. Here we employ the same modeling approach at other longitudes, and compare the results with ionosonde observations obtained from the SPIDR data base for stations in the magnetic latitude range of 40-50 deg.
SA21A-0270
Global ionospheric disturbances during super magnetic storms
Magnetic storms represent the largest disturbances in the magnetosphere and ionosphere. We will present the ionospheric observations by the Millstone Hill incoherent scatter radar, global GPS network, and TIMED GUVI instrument during two super storms. The sudden commencement (SSC) of the 15 July 2000 storm occurred at 19 UT, and the minimum Dst reached -301 nT. The dayside midlatitude ionospheric F region electron density showed a sudden decrease at Millstone Hill and Eglin in response to the SSC. The elevation scan measurements of the Millstone HIll radar show that the sudden decrease in the ionospheric electron density was related to an electron density trough which had an equatorward boundary at Eglin (magnetic latitude 41 degree) at 16 MLT. The formation of the trough may be related to equatorward incursion of the disturbance SAPS electric field. The dayside TEC decreased significantly at the equatorial and upper midlatitudes, and an enhanced TEC band occurred between the depleted regions. The SSC of the 29 October 2003 storm occurred at 07 UT, the storm was further enhanced at 18 UT, and the minimum Dst reached -363 nT. The Millstone Hill radar also detected a sudden decrease of the dayside F region electron density immediately after the storm enhancement. The simultaneous TIMED GUVI measurements show a significant decrease in the O/N2 ratio over the Atlantic sector from the auroral zone to anomaly latitudes, and large TEC depletions occurred coincidentally with the O/N2 decrease. In this second case, both the enhanced electric field and decrease of O/N2 ratio contributed to the depletion of the dayside midlatitude F-region electron density and TEC. The multiple measurements during the two storms reveal the distinct properties and mechanisms of the global ionospheric disturbances.
SA21A-0271
Storm Time Effects on the Low- to Mid-Latitude Ionosphere
The first self-consistent study of the impact of storm-time penetration electric fields on the low- to mid-latitude ionosphere is presented. The inner magnetosphere is described by the Rice Convection Model (RCM) and the ionosphere is described by the Naval Research Laboratory (NRL) code SAMI3. The codes are coupled electrodynamically through the electrostatic potential equation, and the storm is modeled via changes in the polar cap potential. Neutral wind driven electric fields are estimated from the Fejer/Scherliess quiet time model. It is found that temporal changes in the polar cap potential produce electric fields that modify the $F$ region equatorial $E × B$ drift velocities: the velocities increase in the daytime and decrease in the nighttime by up to a factor of two. This causes the total electron content (TEC) in the daytime, mid-latitude ionosphere to increase by up to 35%. In addition, the 'fountain effect' is enhanced in the post-sunset period. \medskip \noindent Research supported by NASA and ONR.
SA21A-0272
Effects of neutral compositions on the ionospheric positive storms during the recovery phase
The ionosonde measurements over Millstone Hill (42.6°N, 71.5°W), Wallops Is (37.9°N, 75.5°W), Eglin Afb (30.4°N, 86.7°W) and Boulder (40°N, 105.3°W) along with simultaneous GUVI/TIMED [O]/[N2] density ratio measurements are analyzed to investigate positive storm effects during the recovery phase of the April 2004 magnetic storm. The results show that the peak density NmF2 increases significantly on 4 April, 2004 (the recovery phase) with respect to the quiet reference days, especially over Boulder. It is generally accepted that the daytime positive storm results from dynamic processes (the neutral winds/electric field effects) that lift the F2 layer, decreases the recombination rate, and increases the electron density. However, this can't explain these observed phenomena on 4 April, where hmF2 doesn't present evident changes during this period. In fact during this period we find an evident increase in the simultaneous TIMED/GUVI [O]/[N2] density ratio. We suggest that the thermospheric composition perturbation should contribute largely to the ionospheric positive storms at middle latitudes during the recovery phase of the April 2004 storm.
SA21A-0273
The dynamics of thermospheric composition and ionospheric total electron content during geomagnetic storms.
The geomagnetic storms of April 17-21, 2002 and May 29-30, 2003 caused large decreases in the O/N2 column density ratio in the thermosphere. For these storms, O/N2 column density decreases of > 50% were observed to extend to mid-to-low latitudes with the FUV sensitive Earth Camera of the Visible Imaging System (VIS) on the Polar spacecraft. Simultaneously in these same regions, the ground-based GPS network observed ~80% reductions in the Total Electron Content (TEC) of the ionosphere. The reduction in the O/N2 column density ratio is due mainly to increases in the molecular species that have welled-Up into the thermosphere from the lower levels of the atmosphere due to auroral heating. The geomagnetic-storm driven increase in molecular densities at typical ionospheric heights rapidly charge exchange with the ambient ionized atoms and subsequently dissociatively recombine with the ionospheric electrons leading to a reduction in the total charge density. The transition boundaries between high and low regions of O/N2 as well as TEC can be tracked in the images and the thermospheric winds can be determined from the motion of the boundaries. The motion of these boundaries during the development of the geomagnetic storm will be discussed.
SA21A-0274
Seasonal effects on negative ionospheric storms at midday
Ionospheric storm effects at midday are examined for 36 prominent geomagnetic storms (Dst < -80 nT) that occurred between 1999 and 2002, using GPS-based total electron content (TEC). It is found that there is a strong seasonal effect on the latitudinal extent of negative TEC storm at midday - negative TEC storms penetrate deeper in latitudes in the summer than in the winter hemisphere. It is also found that the penetration of negative TEC storms is more pronounced for large than small storms. We suggest that large-scale thermospheric circulation and seasonally asymmetric north-south auroral heating are likely the main contributors. It is also shown that enhanced dayside Birkeland currents can also cause ''prompt'' equatorward penetration of negative TEC storms at midday. Our results suggest that thermospheric heating and resulting circulation need to be critically examined to quantify the actual Joule heating enhancement and test whether it is sufficient to overwhelm the prevailing winds.
SA21A-0275
Anomalous Nighttime Plasma Structure in the Recovery Phase of a Superstorm
During intense geomagnetic storms, observations of total electron content using orbiting Global Positioning System receivers and spaceborne radar altimeters suggest that large-scale and large-magnitude dayside increases in ionospheric total electron content can occur within a few hours after the onset of solar wind conditions leading to the storm. Particular storms showing this feature are: October 29, 2003, October 30, 2003, and November 7, 2004. Another feature that has emerged in the study of these superstorms is the presence of significant post-dusk localized TEC enhancements over mid-latitudes, during the recovery phase of the storm, that persist until dawn. We will present measurements from ground and space-based GPS receivers that reveal the characteristics of these localized features, where they appear, their persistence and other characteristics. We speculate that these features are difficult to reproduce using existing models of the Earth's ionosphere in the absence of solar radiation to generate plasma. Nevertheless, they may have significant impact on GPS-based navigation systems affected by the ionosphere.
SA21A-0276
Enhancements of OI 630.0 nm Emission And Ionospheric Tomography Using GPS STEC Measurements During the Period of the Strong Geomagnetic Storm, 2003 Halloween Event in Korea
All-sky camera and GPS measurements were used to investigate the thermosphere and ionosphere during the strong geomagnetic storm period of the 28-31 October 2003. Enhancement in 630.0 nm emission was observed in the northern sky from all-sky images taken at Mt. Bohyun (36.2° N, 128.9° E, geomagnetic latitude = 29°), Korea at 17:48-18:58 UT on 29 October during the main phase of the geomagnetic storm. We show the vertical variation of electron density between 28 and 31 October 2003. The vertical profiles of electron distribution have been examined by the computerized tomographic method using Algebraic Reconstruction Technique (ART). The slant total electron contents (STEC) for ionospheric tomography were measured at the regional GPS reference network of the nine stations that have been operated by Korea Astronomy & Space Science Institute (KASI). The results of ionospheric tomography are compared with Ionosonde measurements and IRI-2001 model. The possible cause of enhancement in 630.0 nm emission and the variation of electron density during the period of the geomagnetic storm will be discussed.
SA21A-0277
Prompt Derivation of TEC from GEONET Data for Space Weather Monitoring
GEONET is the dense GPS receiver network in JAPAN. The data have been used to derive TEC to study ionospheric disturbances in NICT. Quick distribution of the data, within a few hours, has been started recently. We have developed a new method of prompt derivation of TEC from the data and use the TEC distribution over Japan in our daily operation of Space Weather Forecast Center at NICT (RWC Japan of ISES). We will present the outline of the system of prompt derivation of TEC, its performance results, and its capability of monitoring the ionosphere over Japan with some specific events of ionospheric disturbances.
SA21A-0278
Ionospheric Indices Based on GPS TEC
The solar terrestrial environment is presently characterized by a suite of indices that represent the system's dynamics and indicate the degree of space weather effects. These indices an have extended heritage based on measurements that are well calibrated and readily available. Examples of these are the solar radio flux at 10.7 cm (F10.7), magnetospheric currents inferred from ground-based magnetographs (Dst), and auroral electrojet also based on ground-based magnetograms (AE family of indices). At the present time, the ionosphere's dynamics and response to space weather are not characterized by a "true" ionosphere index. However, since ionospheric plasma variability has a major adverse effect on human space technologies, the creation of such an index may be appropriate. The major adverse effects are associated with radio wave propagation through the ionosphere either communications or navigation. Over the past decade thousands of ground-based dual frequency GPS receivers have been deployed. Each of these measures ionospheric total electron content (TEC) continuously in multiple directions. Hence, with the standardized formatting of these measurements and their near real-time nature, a unique ionospheric data stream exists from which indices can, in principle, be developed. This study is an initial exploration of how a purely ionospheric index could be derived from these GPS TEC data. Regional versus global issues are addressed, as well as diurnal issues.
SA21A-0279
ROCSAT Observations of Meso-Scale Density and Flow Undulations in Conjuction with Intermediate-Scale Density Irregularities at Midlatitude Topside Ionosphere
ROCSAT-1 orbiting at 600 km topside ionosphere frequently observes the meso-scale (~50 to 1000 km) ion density and flow undulations at low- to mid-latitudes. During the 8 January 2000 event, noticeable intermediate-scale (1 to 50 km) density irregularities were also observed at midlatitude in conjunction with the meso-scale undulations in many consecutive ROCSAT orbits. The meso-scale density and flow undulations indicate in-phase variations among the radial outward flow, westward flow, and the density enhancement. During these consecutive ROCSAT orbits of observing the meso-scale undulations, the calculated electric field perturbations all point to the northeast-southwest direction at about ° in azimuth. This implies that a frontal structure of the meso-scale disturbance is aligned from northwest to southeast in geographic coordinate. The in-phase undulations of the flow and density variations together with the tilted frontal structure for the meso-scale disturbance fit the predicting result of the Perkins instability [Perkins, 1973]. It could also be caused by the disturbances mapped from plasma cloud instabilities in E region in the model of Hysell et al. [2002] or from the instabilities in the sporadic E layers proposed by Haldoupis et al. [2003] and Tsunoda et al. [2004]. As for the intermediate-scale density irregularities, no correlated phase relationship is found between the density fluctuations and the flow variations. From the fact that the occurrences of the intermediate-scale irregularities are isolated from the meso-scale undulations, we conclude that the cause of the intermediate-scale irregularities should be different from what triggered the meso-scale undulations. The possible interaction between the two triggering mechanisms for the irregularities of the two different scales will be discussed.
SA21A-0280
The Study of Spread F and GPS Phase Fluctuation at Taiwan
This study focus on spread F and GPS phase fluctuation at Taiwan where is north equatorial ionization anomaly (EIA) region. The data came from an ionosonde (24.95 N, 121.23 E) and a GPS receiver (25.17 N, 121.57 E) both setup at north of Taiwan and the observation period was from 1996 (solar minimum year) to 2000 (solar maximum year). The spread F were divided into two category, range spread F and frequency spread F, and performed statistic analysis which include monthly and nighttime variation. Analogously, GPS phase fluctuations were divided into three levels to represent irregularity strength and performed same process as spread F. It is the first time to compare GPS phase fluctuations with ionosonde spread F in the EIA region, and the results of comparison show many interesting points and worth to study more detail.
SA21A-0281
Equatorial Anomaly TEC Observation in China
Since May 2005, a GPS receiver chain had been established at equatorial anomaly region in China. The chain is composed of 4 GPS receivers located at Fuzhou XiamenGuangzhou and Nanning. Shown in the following are geographic and geomagnetic coordinates of the 4 stations. 1,Fuzhou: (26.1N, 119.3E--14.4N, 188.4E); 2,Xiamen: (24.5N, 118.1E--13.2N, 187.4E); 3,Guangzhou: (23.1N, 113.2E--11.8N, 182.8E); 4,Nanning : (22.8N, 108.3E-- 11.4N, 178.2E). The aim of the observation is to study the TEC and ionospheric scintillation at equatorial anomaly in China area. This paper presents a preliminary result of TEC observed with the chain, including geomagnetic quiet times and TEC response to geomagnetic storms.
SA21A-0282
Characteristics of Plasma Depletions Over Indian Region During Solar Maximum
The all sky imaging observations from Kavalur $(12.56° N, 78.8° E)$, India during February-April in 2002 showed the occurrence of plasma depletions in several consecutive nights. Depletions were present in 630.0 and 777.4 nm for about 80% of the total nights of observation. Out of this, about 70% of the nights showed depletions in 557.7 nm also. There was no significant geomagentic activity during the period. The h'F variation obtained from Trivandrum (7.6 °N, 76.9°E) showed rapid upward motion of F-layer in the post-sunset hours, with vertical velocity in the range 30-70 m/s, and an average value of 41 m/s. About 37% of the nights of depletions in 630.0 nm showed the midnight/post- midnight generation of irregularities within the field of view. In contrast to 630.0 and 777.4 nm, depletions were seen in 557.7 nm around midnight or in the post-midnight hours. Simulations confirm that during solar maximum the thermsperic component of 557.7 nm emission dominates over its mesospheric counterpart in the post-midnight hours, while in solar minimum, the mesospheric component is higher throughout the night.
SA21A-0283
Particle and field characteristics of broadband electrons observed by the FAST satellite during geomagnetic storms
Broadband electrons represent remarkable flux enhancements of precipitating electrons over a broad energy range of 30eV-30keV near the equatorward edge of the aurora oval during geomagnetic storms. These flux enhancements were initially reported using particle data of the DMSP satellites, which did not measure pitch angle distribution of precipitating electrons. Here, we investigate broadband electrons using data from the FAST satellite. Sixteen events of broadband electrons were identified from the electron energy spectra for large geomagnetic storms between September 1996 and March 2004. We analyzed in detail energy, pitch angle distribution, and wave spectra during the broadband electron event of July 15, 2000, observed at an altitude of ~2000 km. This event was observed at ~ 10 minutes after the onset of a substorm during the main phase of a storm. The broadband electrons were not observed in one orbit (~ 133 min.) before and after the event at the same local time. These results suggest rapid particle acceleration occurring in the inner magnetosphere associated with a storm-time substorm. During this event, electron flux parallel to the local magnetic field tends to be higher than the perpendicular flux at a low energy range below 1 keV, suggesting parallel acceleration of low energy electrons at low altitudes near the satellite. At a high energy range above 1 keV, electron fluxes show isotropic or double loss-cone features. In the presentation, we show further details of the distribution function of broadband electrons and field characteristics.
SA21A-0284
Study of Proton cutoffs during geomagnetically disturbed times
It is currently believed that solar energetic particles (SEP) may be accelerated at solar flares and/or at interplanetary shocks driven by coronal mass ejections (CMEs). CMEs also cause intense geomagnetic storms during which the geomagnetic field can be highly distorted.SEP fluxes penetrate the terrestrial magnetosphere and reach specific regions depending upon the geomagnetic field configuration. The cutoff latitude is a well defined latitude below which a charged particle of a given rigidity (momentum per unit charge) arriving from a given direction cannot penetrate. SEP cutoff location can therefore be potentially useful in determining the geomagnetic field configuration. This paper reports on the measurements of solar energetic proton cutoffs made by two satellites, SAMPEX and Polar during geomagnetically disturbed times. We study select SEP events and compare our measurements with cutoffs calculated by a charged particle tracing code which utilizes several currently used models of the geomagnetic field. The measured SEP proton cutoffs cover a wide range of rigidities and are obtained at high-altitudes by the HIST detector onboard Polar and at low-altitudes by the PET detctor onboard SAMPEX.
SA21A-0285
Modeled Solar Energetic Particle Trapping in the Earth's Radiation Belts During Geomagnetic Storms and Comparison With Observed Energy Spectra
Solar energetic particles (SEPs) may be promptly trapped in the Earth's radiation belts during geomagnetic storms due to shock related compressions in the geomagnetic cutoff (Kress et al. 2004; 2005). As a test of this non-adiabatic mechanism for populating energetic ion belts, SAMPEX energy spectra from newly formed belts between L=2 and L=3 are compared with numerically modeled magnetospheric SEP fluxes. Beginning with an isotropic energetic particle distribution with energy spectra measured on open field lines mapping directly to the solar wind, the formation of new belts is modeled by following test particle Lorentz trajectories in time dependent fields obtained from the Lyon-Feder-Mobarry (LFM) global MHD magnetospheric simulation code.
SA21A-0286
Cluster Observations of Pc 1-2 Waves and Associated Ion Distributions During the October and November 2003 Magnetic Storms
Unusual wave activity in the Pc 1-2 frequency band (0.1-5 Hz) was observed by the Cluster spacecraft in association with the two large geomagnetic storms of late 2003. During the onset of the Halloween storm on October 29, 2003, intense broadband activity between ~0.1 and 0.6 Hz appeared at all 4 spacecraft on both sides of the magnetic equator at perigee (near 1400 UT and 08:45 MLT). Power was especially strong and more structured in frequency in the compressional component: a minimum in wave power was observed at 0.38 Hz, corresponding to the oxygen ion cyclotron frequency. Poynting vector calculations indicated that wave power was primarily directed radially outward rather than along the magnetic field. Narrowband purely compressional waves near 0.15 Hz appeared at higher dayside latitudes in the southern hemisphere. CIS ion spectrometer data during this pass revealed that O$^+$ was the dominant energetic ion. During the recovery phase of the November storm, on November 22, 2003, predominantly transverse 1.8 Hz waves with peak-to-peak amplitude of 10 nT were observed by all four spacecraft near perigee at L = 4.4. During this more typical Pc 1 event, wave power was directed along {\bf B}, toward the northern ionosphere. An unusually polarized 2.3 Hz emission (with power in the radial and compressional, but not azimuthal directions) was observed at L = 5.4-5.9, 10-15° south of the magnetic equator. We infer that this wave event may have been generated on lower L shells and propagated obliquely to Cluster's location. Consistent with other recent observations, anisotropic plasma sheet / ring current proton distributions appeared to be a necessary condition for occurrence of waves during both passes, but was not always a sufficient condition. The transverse waves of Nov. 22 occurred in regions which also contained greatly increased fluxes of cool ions (E < 1 keV). On both days Cluster observed features not previously reported, and we note that the purely compressional nature of the October 29 events was not anticipated in previous theoretical studies. The fact that these unusually polarized waves occurred in association with very intense geomagnetic storms suggests that they are likely to be extremely rare.
SA21A-0287
The Effects of Lower Hybrid Waves on Ring Current Protons During Periods of Magnetic Disturbance
Plasma wave data from the ISIS-1, ISEE-1, DE-1, and CLUSTER spacecraft suggest that the magnetosphere from L = 2 to L = 7 is commonly populated by small scale ( 2 - 100 m), small amplitude (0.1 - 1%) magnetic field aligned plasma density irregularities. Whistler mode waves propagating through regions containing these irregularities are commonly observed to excite lower hybrid waves through linear mode coupling as the irregularities scatter the whistler mode waves. During periods of magnetic disturbance intense whistler mode waves, such as ELF/VLF chorus, are generated near the magnetic equatorial plane on L shells in the range 3 - 7 and propagate towards lower latitudes. It can be expected that the intense chorus waves will also excite intense lower hybrid waves through linear mode coupling as the chorus waves propagate through regions containing the small scale irregularities. The excited lower hybrid waves generally have the appropriate phase velocities to interact with ring current protons through the transverse Landau resonance. In the present paper we calculate the pitch angle scattering of ring current protons due to transverse Landau interactions with lower hybrid waves excited through linear mode coupling during magnetically disturbed periods. We find the conditions under which this interaction could play an important role in determining the life time of ring current protons.
SA21A-0288
Relationship of the ring current plasma pressure from ENA images and field-aligned currents
The steady state MHD force balance equation and current continuity show that pressure gradients in the equatorial ring current are associated with field-aligned currents (FAC) for large spatial and slow temporal scale changes of the magnetic field. To obtain the ring current pressure, ion distributions are inverted from ENA images obtained by IMAGE/HENA and MENA and used to calculate the plasma density, temperature, and pressure for a series of geomagnetic storms/substorms on 22 January, 12 February, 9 and 10 March, 29 May, 23 September and 13 October in 2004. FAC patterns in the high-latitude ionosphere are derived from the Weimer 2005 FAC model with time shifted solar wind and IMF driven input parameters. Comparing the ring current pressure with the field-aligned current pattern mapped to the equator shows the dynamics of the relationship between the plasma pressure/pressure gradients and field-aligned currents for the series of storms/substorms addressed in this presentation.
SA21A-0289
Ring Current Asymmetry as Observed by Ground Magnetometers, In Situ, and Space-based Remote Sensing Data
During enhanced geomagnetic activity, the ring current is well-known to exhibit a strongly asymmetric structure. Some storm models predict a rapid change to symmetric ring current in early recovery, but this is not always what is seen. In particular, many use the ASY index to characterize the inner magnetospheric ring current morphology, as it is widely available and continuous, though it is not clear how well it represents what is actually occurring in the inner magnetosphere. The increased availability of in situ and remote sensing measurements from instruments on spacecraft such as POLAR and IMAGE, has given physicists the opportunity to re-evaulate the meaning and usefulness of such indices and gain a better understanding of the ring current morphology. The asymmetric index (ASY), in particular, is analyzed to evaluate its usefulness in parameterizing the asymmetry of the storm-time ring current. Data used for this evaluation include POLAR CAMMICE and LANL in situ data and IMAGE HENA data. We analyze the ring current morphology in storm times and discuss whether ASY provides a useful characterization.
SA21A-0290
Reinterpreting the Burton-McPherron-Russell Equation for Predicting Dst
The simple equation proposed by Burton et al. [1975] and extensively applied with considerable success for predicting the time series of the geomagnetic storm index $Dst$ is generally derived solely from conservation of energy: the total energy in the ring current plasma, related to $Dst$ by the Dessler-Parker-Sckopke theorem, is calculated from a solar-wind-controlled energy input (source) rate and an effective loss rate, without describing the specific energization processes. More recently, numerical simulation models of ring current evolution have relied on the opposite approximation: they describe the energization (particle drifts under solar-wind-controlled electric fields) and loss processes, without imposing conservation of energy. The fact that, despite their different underlying assumptions, predictions of $Dst$ by both methods agree reasonably well with each other and with observations suggests that some of the assumptions need to be reexamined. The Dessler-Parker-Sckopke theorem, in its generalized form, contains a magnetotail surface term proportional to the open magnetic flux, the time derivative of which equals the difference between the electric field integrals along the dayside and along the nightside reconnection lines. The dayside integral contributes a term to the equation for $(d/dt)Dst$ that is identical in form and (within the uncertainties) consistent in magnitude with the empirically determined source term of the Burton-McPherron-Russell equation. The success of the empirical equation in predicting $Dst$ then implies that the two remaining source terms in the theoretical equation, the contribution of the nightside integral in the magnetotail term and the rate of increase of plasma energy content, sum to zero (at least approximately); this is equivalent to the statement that the amount of kinetic energy being added to the ring current plasma equals a fraction $X/{\mathcal L}_{MT}$ of the magnetic energy being removed from the magnetotail by nightside reconnection ($X ~ 10 {\mathrm R_E} =$ distance between Earth and the inner edge of the magnetotail, ${\mathcal L}_{MT} =$ effective length of the magnetotail). The simplest interpretation is that the energy of ring current plasma is indeed being supplied primarily from the magnetotail by processes that involve nightside reconnection in an essential way.
SA21A-0291
Self-consistent Modeling of Magnetic Fields and Plasmas in the Inner Magnetosphere During Geomagnetic Storms
Observations as well as computational simulations show that during a magnetic storm the magnetic field in the inner magnetosphere on the night side can be very stretched compared to a dipole. This is why a magnetically self-consistent treatment of plasma transport is crucial during such events. In this work we extend our previous ''1-way'' coupling between a kinetic ring current model and a magnetospheric equilibrium model (in which force-balanced fields are computed using the pressures from the kinetic model) to a fully magnetically self-consistent approach in which the force-balanced fields are fed back into the kinetic model to guide its continued evolution. The self-consistent approach is then applied to the simulation of the April 22, 2001 storm, one of the GEM Storm Challenge events. The results use boundary and initial conditions for the kinetic model from several spacecraft, as well as magnetic flux boundary conditions for the equilibrium model from the empirical model of the geomagnetic field T89. The results obtained with this self-consistent approach are fundamentally different from runs of the kinetic model with a dipolar background. The most significant features of the self-consistent results are lower plasma transport and plasma pressure in the inner magnetosphere (about half of that obtained with the dipole) and local, narrow pressure peaks as well as significantly enhanced plasma β in localized regions on the night side.
SA21A-0292
SC related electric and magnetic field variations in the inner magnetosphere and plasmasphere regions
Electric and magnetic field variations inside the plasmasphere associated with SCs identified on the ground are analyzed based on the Akebono satellite observations which have been carried out more than 13 years since March 1989. 153 electric field observation data corresponding to SCs show abrupt change of intensity as well as direction within a few minutes inside the plasmasphere. Temporal variations of the electric field showed a bipolar waveform with the amplitude range of 0.2-38 mV/m. The electric field signature is followed by a dumping oscillation with the period of Pc3-4 ranges. The magnetic field variations of 33 SCs also show an abrupt increase of 0.2-65 nT within a few minutes, which indicate the compression of the magnetosphere due to the discontinuity of solar wind. The initial excursion of the electric field during SCs tends to be directed westward. The amplitude does not show a dependence on magnetic local time that has been observed outside the plasmasphere. The magnitude of the electric field variations tends to be proportional with the power of 0.65 to the magnetic field variation in the plasmasphere. The Poynting vector of the initial SC impulse is directed toward the earth, which suggests that energy of magnetic disturbances associated with SCs propagates toward the earth inside the plasmasphere with the refraction due to the plasma density gradient. One of the most interesting results from the present study is that a DC offset of the Ey component of the electric field appears after the initial electric field impulse associated with SCs. This signature is interpreted to be a magnetospheric convection electric field penetrates into the inner plasmasphere (L=2.5). The intensity of the offset of the Ey field gradually increases by 0.5-2.0 mV/m about 1-2 minutes after the onset of the initial electric field impulse and persists about 10-30 minutes.
SA21A-0293
The Influence Of Substorm-Induced Electric Fields On The Build-Up Of Particle Radiation During Geospace Magnetic Storms
The enhanced magnetospheric convection electric field and the substorm-induced electric fields are the drivers of plasma acceleration during geospace magnetic storms. The relative influence of the two drivers on the development of the storm-time ring current is the topic of this study. We use a three-dimensional dynamic ion-tracing model, to construct maps of the temporal and spatial variations of ion number densities in the inner magnetosphere. Outflowing ionospheric oxygen ions and protons are traced under two distinct scenarios: in the first case, we follow their transport and acceleration under the influence of a large convection electric field only. In the second case, an impulsive electric field is added due to magnetic field dipolarization, as observed by spacecraft during substorm expansion. Plasma sheet particles are also traced under the above conditions. According to this study the inclusion of substorm-induced electric fields renders ion acceleration much more efficiently. The difference in energization is much more prominent for O+ ions, which have been observed to be preferentially accelerated by substorm-induced electric fields. For both ion species large-scale magnetospheric convection alone is not sufficient to accelerate these particles to ring current energies.
SA21A-0294
The response of the inner magnetospheric electric field to global stormtime ionosphere-thermosphere changes
The interaction between the solar wind and magnetosphere imposes a convection electric field across the magnetosphere. This electric field is associated with the region-1 Birkeland currents and is called the "driving" or the "convection" field. A second electric field, called the shielding field, is generated by the region-2 Birkeland currents. The strength of this electric field is related to both the density gradient along the inner edge of the plasma sheet and the conductivity of the ionosphere. The "penetration" electric field is the difference between the convection field and the shielding field. During magnetic storms, the ionospheric conductivity changes due to changes in auroral particle precipitation and the global ionospheric response. This study examines the impact on the subauroral electric field caused by conductivity changes that are part of the global ionospheric-thermospheric (IM) response to the magnetic storm. Using time-varying conductances calculated from the Thermosphere-Ionosphere-Mesosphere-Electrodynamics General Circulation Model (TIME-GCM) in the Rice Convection Model, the impact of the global IM response upon the development of the subauroral electric field is investigated.
SA21A-0295
Analysis of the Octuber 3-7 2000 GEM Storm with the WINDMI Model
he 8 dimensional physics model WINDMI is used to analyze the October 3-7, 2000 geomagnetic storm using solar wind input data from the ACE satellite. This period was chosen because it contains an extended interval of well-defined and quasi-periodic auroral activations called sawtooth oscillations, a phenomena whose relationship to substorm processes and to upstream solar wind drivers is still under debate. The question of whether multiple sawtooth oscillations are triggered by periodic upstream solar wind features or by internal magnetospheric processes is addressed. The model predicts both the occurrence of 8 auroral activations identified as sawtooth events during the 24 hour period on the 4th of October, in agreement with the measured $AL$ index, and also an earlier multiple sawtooth interval on the 3rd of October, in agreement with the measured $AL$ index. These intervals occur during steady but moderate solar wind IMF $B_z$ values and the periodicity of the sawtooth events was not directly related to any periodic features in the upstream solar wind. The model also predicts the geomagnetic $D_{\mathrm{st}}$ index through the main and recovery phase of the storm.
SA21A-0296
Analysis of the October 3-7 2000 and April 15-24 2002 Geomagnetic Storms with the WINDMI model
A computationally optimized model of the magnetosphere-ionosphere system called WINDMI is used to analyze two large geomagnetic storm events, Oct 3-7 2000 and Apr 15-24 2002. These two storms share common features such as the passage of a magnetic cloud, shock events and the occurrence of periodic substorms. The input into the model is a driving voltage derived from the solar wind dynamic pressure and the interplanetary magnetic field measured by the ACE satellite. Two key outputs of the model are (1) the nightside field aligned region 1 current that closes in the auroral ionosphere giving the $AL$ index from the westward electroject and (2) the total energy in the ring current plasma driven by the plasma sheet with losses from the charge exchange of the fast ions which is then converted to the ground based $D_{\rm st}$ signal through the Dessler-Parker-Schopke relationship. The model parameters are optimized using a genetic algorithm to search for solutions that simultaneously have least mean square fit to the $AL$ and $D_{\rm st}$ indices and also possess substorms of period 2-4 hours. Good results have been obtained for both geomagnetic storm periods.
SA21A-0297
Plasma sheet parameters and their statistical relationship to ring current injections
We are interested in understanding the physical process in the plasma sheet and inner magnetosphere during magnetic storms that differentiates ring current injection intervals from non-injection intervals. We contrast plasma sheet plasma parameters during injection intervals to parameters during similar non-injection intervals. Looking at the temperature, density, and pressure alone is misleading, since variations in these quantities may be due to variations in the level of magnetic stretching, which would adiabatically alter the plasma moments and/or cause apparent variations due to changes in magnetic field mapping. In order to best account for these, we use a Tsyganenko magnetic field model to estimate the effect of the magnetic field, and calculate adiabatically invariant quantities to represent the pressure, temperature, and density. The results of the study seem to show that the invariant pressure and invariant density are lower than usual during ring current injection intervals, while the invariant temperature is apparently not significantly different. The implications and physical interpretations of the results as they relate to magnetic storms will be explored.
SA21A-0298
Variability Of The Center Of The Equatorial Electrojet At West African And Indian Sub-Sectors As Obtained From A Thick Current Shell Model
A tested thick current shell model format of Equatorial electrojet, an intense current flowing eastward in the low latitude ionosphere within the narrow region flanking the dip equator, have been used to evaluate the hourly values of the center of equatorial electrojet at the West African and Indian sub sectors. The thick current shell model, which takes into account the vertical ionospheric currents, were used to fit data of equatorial electrojet indices obtained from ground observations. The equatorial electrojet center exhibits diurnal and seasonal variations at both sectors. At the Indian sector, the center of EEJ is observed to migrate northwards towards the dip equator from the dawn such that it is closer to the dip equator at about local noon and then recline southwards towards the dusk. The variability of the jet center is explicable in terms of the meridional winds. The model results tallied with the satellite observations.