SM13A-1181 1340h
Low altitude ENA emissions observed from various vantage points on IMAGE
Interaction between the atmosphere and proton precipitation from the ring current results in proton ENA emission into space, due to an effective reflection from the atmosphere. Observation of this emission from the orbiting IMAGE spacecraft is strongly dependent upon the location of the spacecraft, because the emission is non-isotropic and the flux of reflected ENAs is therefore non-homogeneous in space. We have presented observations of reflected ENAs taken when IMAGE was at relatively low altitude. In this paper we will present results from a wider range of IMAGE altitudes. We present latitude distributions of the reflected ENA source along with estimates of the pitch angle distributions at the source location. We will discuss these results in terms of the reflection process and what we can learn about the proton precipitation by studying the reflected ENA distributions.
SM13A-1182 1340h
Geomagnetic Activity Dependence of the Ratio N+/O+ in the Ring Current
Based on the energetic particle measurement obtained by CRRES/MICS, ion composition variations in the ring current have been investigated. Observation shows that in addition to O+ and H+, N+ ions are also an important composition in the ring current region. The ratio of N+/O+ during geomagnetic quiet times is about 0.26, while a smaller valued could be found for strong active times. The variation of the ratio follows the same trace as the Dst index. Through a statistic study, it is demonstrated that the ratio of N+/O+ decreases with an enhanced geomagnetic activity for strong storms, whereas for small storms, there is no obvious correlations of the ratio to the activity level. Based on the IRI model, we show that different ion species reach their peak values at different altitude. The maximum of oxygen ions sit in a lower altitude than that of nitrogen ions. It is thus implied that the altitude of the ion up-flowing in the ionosphere is closely related to the geomagnetic activity. The stronger storms, the lower ionosphere could be involved in the magnetosphere-ionosphere coupling.
SM13A-1183 1340h
Investigation of the Effects of IMF Orientation Upon Delivery of Plasma Sheet Material to the Inner Magnetosphere
The orientation of the interplanetary magnetic field (IMF) is known to strongly control the entry of solar wind material into the Earth's magnetosphere. Within the magnetosphere various plasma properties and parameters are known to be IMF dependent. In this study we use Magnetospheric Plasma Analyser (MPA) data from the LANL constellation of satellites located in geosynchronous orbit, in conjunction with the imaging capabilities of the Medium Energy Neutral Atom (MENA) imager on-board the IMAGE satellite, to determine the effects of IMF orientation on the transport of plasma from the plasma sheet into the inner magnetosphere. A statistical study of MPA data is performed to determine bulk plasma properties at geosynchronous orbit in relation to IMF-By and IMF-Bz. In a parallel statistical study we use MENA data to determine the location of the peak nightside energetic neutral atom (ENA) emissons and to investigate whether this peak, which may indicate substorm injection regions, is IMF-dependent.
SM13A-1184 1340h
Multi-Spacecraft Comparisons of Intense Activity at Low Auroral Latitudes During Major Geomagnetic Storms
Major geomagnetic storms (DST $<$ $\sim$ -200 nT) while quite rare (only $\sim$18 have occurred within the past 5 years) produce dramatic activity within most regions of the earth's magnetosphere, providing an opportunity to study the coupling of these different regions under extreme conditions. Possibly the most prominent type of activity common to such storms is a variety of aurora at low auroral zone latitudes, well equatorward of the standard Region I/II current systems. We present results of a study of such events where intense downgoing electron fluxes are observed in the FAST spacecraft data at altitudes of 3000-4000 km. We compare the particle distributions, and electric and magnetic wave characteristics at FAST during these events with concurrent data from spacecraft which are located at similar latitudes and local times to FAST but in more distant regions of the magnetosphere, at 5-10 R$_{E}$, including the Cluster, Polar, and several geosynchronous satellites. We also compare the in situ data with spacecraft auroral images. In particular, we investigate how observed low latitude aurora and their associated downward electron flux at FAST altitudes are coupled to conditions at 5-10 R$_{E}$ during major geomagnetic storms.
SM13A-1185 1340h
Multi-point observations of density structures in the polar cap
We investigate properties of plasma density irregularities in the polar cap at a radial distance of 5 Earth radii. Our analysis is primarily based on multi-point observations of auroral hiss. We analyze high resolution data of the wave instruments on board the four Cluster spacecraft. The local electron density is estimated, obtaining values close to 1 particle per cc, with density depletions decreasing down to one tenth of the density of the surrounding polar cap plasma. Combined analysis in different points in space gives us the orientation of the normal direction to these structures, the velocity of their drift, their size, and lifetime. We show that the density structures move at speeds of a few km/s. The corresponding convection electric field in the polar cap is then approximately 1 mV/m, consistent with the values expected based on previous observations by different methods. If we map the transverse dimension of the density depletions to the ionospheric heights, we obtain values of the order of a few tens of km. Their lifetime is often longer than tens of seconds.
http://terezka.ufa.cas.cz/santolik/papers/agu2004
SM13A-1186 1340h
A model on the interaction of magnetospheric relativistic electrons with Ultra-Low-Frequency (ULF) Waves
Recent paper by Tan, Fung and Shao [2004] shows evidences of resonant interaction and acceleration of energectic electrons with PC5 ULF waves (1-10 mHz) by analyzing CRRES and GOES satellites observations for Aug. 27, 1991 event. The event shows energetic electron flux being modulated and enhanced in 2 hours. In this presentation, we present a model of characteristic distributions of toroidal and poloidal waves in the equatorial plane during the event. By tracing particles in the electric field mapped out with CRRES observations using this model, we compared details of energetic electron flux variation to those observed by CRRES. We will also compare efficiencies of acceleration by toroidal wave to those by poloidal wave. Discussions will be given on furtehr implications of the model. Tan, L. C., S. F. Fung, and X. Shao (2004), Observation of magnetospheric relativistic electrons accelerated by Pc-5 ULF waves, Geophys. Rev. Lett., L14802, doi:10.1029/2004GL019459.
SM13A-1187 1340h
Seasonal Variations of Atmospheric Electricity Measured at Amundsen-Scott South Pole Station
This paper investigates seasonal variations of the vertical electric field and current density as measured at the South Pole between 1991 and 1993. After initial data reduction, a model approach was used to decouple the magnetospheric and atmospheric components of the measurements. This approach calculated and subtracted the polar-cap ionospheric potential from the measured data to obtain a signal of global tropospheric origin, in principle. The diurnal variations of the resulting data were averaged as a function of UT. These averages were calculated for the data as a whole and for the date sorted and binned by season and by magnetic activity level. The seasonally-binned average results are consistent with recent papers indicating that the electric field measurement show global convective-electrical activity to be a minimum during the northern hemisphere winter, in contradiction to the original 1929 Carnegie data. Because the electric field was a maximum during the northern hemisphere summer season, the mid-latitude regions must contribute more strongly than the tropics to global atmospheric electricity. This analysis supports the link of electrical activity to global temperature. The magnetic activity binned results suggest that the polar cap potential model used under estimates the cross polar cap potential when there is a high Kp index. This result can be explained if the model did not have equal weighting across the Kp range or if the limitation on the spherical harmonic coefficients did not give the potential at the South Pole. A complete high-latitude model is needed in order to estimate saturation of the cross-cap potential, as some theories predict.
SM13A-1188 1340h
The Relationship Between Chorus and Enhanced Relativistic Electron Fluxes in Geomagnetic Storms
It has been suggested that whistler mode chorus waves play a role in the acceleration and loss of radiation belt electrons during geomagnetic storms. In a previous statistical study of chorus received at Halley, Antarctica (76$^\circ$S 27$^\circ$W, $L$$=$$4.3$), during storms of the solar cycle 1992--2002, we found that on average chorus intensities were significantly enhanced in the storm recovery phase. In this paper we extend that study to provide stronger evidence of the link between chorus and electron acceleration. We selected a set of 244 storms in 1992--2002 having a minimum $D_{\rm st}$ less than $-50$~nT, for which average 1.8--3.5~MeV electron fluxes 2--3 days after the storm were available from the LANL satellites. This set was classified into two subsets according to whether the flux was less than or greater than an arbitrary threshold of 0.5 electrons cm$^{-2}$s$^{-1}$sr$^{-1}$keV$^{-1}$. A superposed epoch analysis of the whole set, using the times of minimum $D_{\rm st}$ as the set of epochs, reproduced the results of the earlier study, but when the two subsets were analysed separately, it was found that for the lower frequency channels, 0.5--1.0~kHz, characteristic of the main chorus band, the average intensities of chorus observed were larger for storms when the post-storm flux was high, consistent with theories that chorus is at least partly responsible for accelerating the electrons. Near the top of the chorus band (2.0 kHz) in the first 12 hours of the recovery phase, the reverse was the case; we explain this in terms of the opposing effects of a chorus source function with a frequency-dependent time constant, and a propagation function representing the wave attenuation between the source region in the magnetosphere and the receiver on the ground. A long (several-day) post-storm depression of wave power at frequencies above the chorus band is attributed to increased precipitation from the radiation belts, affecting absorption of radio atmospherics from tropical thunderstorms propagating to the receiver. The depression was greater for the set of storms characterised by high post-storm fluxes, which strengthens this interpretation. It was accompanied by longer lasting geomagnetic and substorm activity after the storm, as indicated by the $K_{\rm p}$ and $AE$ indices, consistent with recent suggestions that relativistic electron acceleration is more likely to occur in storms with substantial substorm activity in the recovery phase.
SM13A-1189 1340h
Scattering of Trapped Electrons by VLF Waves During a Magnetic Strom
The Source/Loss Cone Energetic Particle Spectrometer (SEPS) on the NASA Polar satellite measures particle fluxes with high angular resolution (1.5 deg) near the atmospheric loss cone. During the weak magnetic storm (Dst=-40 nT) of September 10, 1996 the trapped electron fluxes increased, and the angular distributions of down-going 150 keV electrons extended well inside the atmospheric loss cone. Simultaneous measurements of up-going electrons showed empty loss cones. These loss cone fluxes were observed at MLT of ~14 hrs, latitude near 45 deg, and L between 4 and 6.5, the extent of the diffusion into the loss cone increasing with increasing L. Wave measurements with the Plasma Wave Instrument, also on the Polar satellite, showed strong VLF hiss and chorus at the time of the pitch angle diffusion. The enhanced waves and electron precipitation persisted for several days. These observations support the original Kennel and Petschek (JGR 71, 1, 1966) concept that an increase in trapped electron flux would initiate wave growth and loss of particles by pitch angle scattering. However, in this case the waves did not propagate parallel to the magnetic field and thus would couple waves and particles at different L values.
SM13A-1190 1340h
Relativistic electron flux enhancement on October 28, 2003
Abrupt enhancement of relativistic electron (E$>$2MeV) flux was observed by geosynchronous and polar orbit satellites at ~11:50 UT on Oct. 28, 2003 after an intense X17 solar x-ray burst at 11:10 UT. The relativistic electron enhancement occurred before the magnetic storm starting at 6:00 UT on the next day and was directly correlated with the Solar Energetic Particle (SEP) event in the upstream solar wind. Observations by SAMPEX (E$>$1MeV) and NOAA/POES (E$>$0.3MeV) polar satellites show that the abrupt electron enhancement extends across all high L-values (L$>$6) with no notable time difference. The increase of electron flux lasted for more than one day, with its peak being clearly in conjunction with the arrival of an interplanetary shock at the Earth. Obviously, these relativistic electrons were not accelerated by the varying electric fields in geospace associated with development of the storm. Measurements from ACE/EPAM and SOHO/COSTEP experiments indicated that the enhancement of energetic electron with energy being a few hundreds keV in the solar wind was seen simultaneously with the increase of relativistic electron flux at high L-values in the Earth. Therefore the observations presented in this paper strongly suggest that the MeV electrons in the solar wind may provide an additional source for the relativistic electron in the magnetosphere.
SM13A-1191 1340h
Ring-Current Ion Angular Distributions: CAMMICE Observations
The evolution of ring current ion angular distributions is important to understanding transport and loss process. It is also important for understanding ENA images. Chen et al. Compared 40 - 150 keV proton pitch angle distributions with simulations involving transport and charge exchange losses (Chen et al., 1998, 1999). The He+ and O+ ions were not examined in those papers. Recent work has shown that at lower energies (below 5 to 25 keV) the ring current ions often have field aligned angular distributions in the inner magnetosphere. In the current study we examine the ring current ion angular distributions for H+, He+, He++ and O+ over the wide energy range (1 to 200 keV/q) covered by the Polar CAMMICE observations. For example, during a quiet period on 9 May 1999 the H+ and He+ angular distributions at 40 keV/q could be represented by Sin$^{N}$(alpha) with N=0.6 and 2.9 respectively at L=3.5 while N=0.25 for both near L=6.5. During quiet times, the O+ fluxes were too low to obtain a valid fit on short time scales. During the May 4, 1998 magnetic storm CAMMICE observed bi-directional field-aligned $<$ 10 keV H+, He+ and O+ ions for more than 30 minutes at L$<$6 Re while observing distributions peaked at 90 deg. for higher energies. We will provide such snapshots of the ring current ion angular distributions during both quiet and storm times plus statistical average angular distributions for the dominate species.
SM13A-1192 1340h
Remote-sensing and In Situ Study of Inner Magnetospheric Coupling During Storms and Substorms
During storms and substorms, the inner magnetosphere responds as a globally-coupled system. The components of this system are the plasmasphere, ring current, plasma sheet, and ionosphere. We present observations by IMAGE (which provides global snapshots of the plasmasphere, ring current, and aurora), by ground-based GPS receivers (which measure total electron content), and by in situ spacecraft both at geosynchronous orbit (i.e., LANL) and at ionospheric altitudes (i.e., DMSP). During mild storms with little or no substorm activity, (e.g., 17-18 June 2001) the inner magnetosphere responds mainly to external driving by the solar wind and IMF. During substorms (e.g., 17 April 2002) the inner magnetosphere evolves under the influence of both external and internal processes. We examine the coupling between the high-altitude equatorial plasmapheric plasma, and the ionospheric plasma at the footpoints of the magnetic field lines that pass through the plasmasphere. Weak coupling would result in, among other things, an altitude-dependent L-value for the location of the plasmapause. Strong coupling might occur especially during times when strong region 1 and region 2 current systems are in place.
SM13A-1193 1340h
Mid-latitude hiss and plasmaspheric notch
A newly identified whistler mode ELF/VLF emission, observed by the Cluster satellites, will be presented. In the vicinity of the plasmapause, around the geomagnetic equator, the four Cluster satellites often observe banded hiss-like electromagnetic emissions (BHE). Their frequency bandwidth is always in between the lower hybrid resonance and the electron gyrofrequency, from 2 kHz to 10 kHz. Based on two years of data measured by three waves experiments on Cluster (WHISPER, STAFF and WBD), the following properties of the BHE waves have been deduced: (i) their location is strongly correlated with the position of the plasmapause, (ii) no MLT dependence has been found, (iii) their spectral width is generally 1 to 2 kHz, and (iv) the central frequency of their emission band varies from 2 kHz to 10 kHz. All these features suggest that BHE are in fact mid-latitude hiss emissions (MLH). MLH have been rarely observed on a regular basis at such altitude. Based on this survey, the central frequency of mid-latitude hiss is shown to be correlated with the Kp index. This suggests either that these banded emissions are generated in a given f/fce range, or that there is a Kp dependent Doppler shift between the satellites and a possible moving source of the MLH Mid-latitude hiss case events observed within density depletion known as plasmaspheric notch (observed by the EUV instrument on IMAGE) will be presented. A recent study showed that plasmaspheric notch plays a crucial role in the generation of higher frequency emissions such as kilometric continuum. The role of plasmaspheric notch in the generation and/or the amplification of mid-latitude hiss will be addressed.
SM13A-1194 1340h
Redistribution of the Stormtime Ionosphere and the Formation of a Plasmaspheric Bulge
Storm enhanced density (SED) and plasmasphere drainage plumes resulting from the erosion of the plasmasphere boundary layer by sub-auroral disturbance electric fields have been identified from both ground and space. Here we examine the source region of the erosion plumes - seen as a localized enhancement of total electron content (TEC) in the post-noon plasmasphere/ionosphere at the base of the plume. Observations suggest that this enhanced TEC results from a poleward redistribution of dusk-sector low latitude thermal plasma during the early stages of a strong geomagnetic disturbance. Ground based and low-altitude observations with GPS TEC, incoherent scatter radar, and DMSP in situ observations are combined with F-region TEC observed by the Jason and Topex satellites to provide details and a temporal history of the evolution of such events. Seen from space by IMAGE EUV magnetospheric imagery, the region of enhanced TEC appears as a pronounced brightening in the inner plasmasphere. IMAGE FUV observes the associated disturbance of the low-latitude F region as a localized enhancement of the equatorial anomalies, and provides complementary images of this inner-plasmasphere/ionosphere feature. These effects are especially pronounced over the Americas and we suggest that this results from a strengthening of the equatorial ion fountain due to the effects of undershielded (penetrating) electric fields in the vicinity of the South Atlantic magnetic anomaly. The enhanced features, seen both from the ground and from space, corotate with the Earth once they are formed. The high-TEC plasma in these regions forms a source for the dense erosion plumes which occur during strong disturbance events.
SM13A-1195 1340h
Cluster Observations Whistler-mode Propagation Inside and Outside the Plasmasphere
ELF/VLF Chorus emissions and lightning- generated whistlers are two types of whistler mode waves commonly detected in the inner regions of the Earth's magnetosphere. Lightning-generated whistlers are generally observed in the region 2$<$L$<$6, while chorus is generally observed in the region 4$<$L$<$6. Studies of ELF/VLF chorus emissions observed near the magnetic equator have shown that their sources can be closely localized in space , while whistlers are known to be generated by lightning strikes on Earth, and can travel relatively longer distances into the magnetosphere with relatively broad wave fronts. Recently the Cluster spacecraft have provided a unique opportunity to obtain four simultaneous measurements of these ELF/VLF whistler mode waves at four separate points in space. In the present paper we use CLUSTER data to compare the time signatures of both chorus emissions and whistlers in order to determine how the spectral properties of these waves vary with position. In particular we determine differences in the frequency spectrum of the lightning-generated whistlers, both inside and outside the plasmasphere, and use these differences to test the hypothesis that whistlers propagating outside the plasmasphere are often strongly coupled to lower hybrid waves in regions where the plasma density profile is irregular. In the case of chorus emissions, we compare the frequency shifts of individual chorus elements as measured on the CLUSTER spacecraft and use this data to determine the spatial and temporal characteristics of the chorus source regions
SM13A-1196 1340h
Data-based Modeling of the Dynamical Inner Magnetosphere During Strong Geomagnetic Storms
This work builds on and extends our previous effort [{\it Tsyganenko et al.,} 2003] to develop a dynamical model of the storm-time geomagnetic field in the inner magnetosphere, using space magnetometer data taken during 37 major events in 1996--2000 and concurrent observations of the solar wind and IMF. The essence of the approach is to derive from the data the temporal variation of all major current systems contributing to the geomagnetic field during the entire storm cycle, using a simple model of their growth and decay. Each principal source of the external magnetic field (magnetopause, cross-tail current sheet, axisymmetric and partial ring currents, Birkeland currents) is controlled by a separate driving variable that includes a combination of geoeffective parameters in the form $N^\lambda V^\beta B_s^\gamma$, where $N$, $V$, and $B_s$ are the solar wind density, speed, and the magnitude of the southward component of the IMF, respectively. Each source was also assumed to have an individual relaxation timescale and residual quiet-time strength, so that its partial contribution to the total field was calculated for any moment as a time integral, taking into account the entire history of the external driving of the magnetosphere during each storm. In addition, the magnitudes of the principal field sources were assumed to saturate during extremely large storms with abnormally strong external driving. All the parameters of the model field sources, including their magnitudes, geometrical characteristics, solar wind/IMF driving functions, decay timescales, and saturation thresholds were treated as free variables, to be derived from the data by the least squares. The relaxation timescales of the individual magnetospheric field sources were found to largely differ between each other, from as large as $\sim$30 hours for the symmetrical ring current to only $\sim$50 min for the region~1 Birkeland current. The total magnitudes of the currents were also found to dramatically vary in the course of major storms, with the peak values as large as 5--8 MA for the symmetric ring current and region 1 field-aligned current. At the peak of the main phase, the total partial ring current can largely exceed the symmetric one, reaching $\sim$10 MA and even more, but it quickly subsides as the external solar wind driving disappears, with the relaxation time $\le$2 hours. The tail current dramatically increases during the main phase and shifts earthward, so that the peak current concentrates at unusually close distances $\sim$4-6$R_E$. This is accompanied by a significant thinning of the current sheet and enormous tailward stretching of the inner geomagnetic field lines. As an independent consistency test, we calculated the expected Dst-variation based on the model output at Earth's surface and compared it with the actual observed Dst. A good agreement (cumulative correlation coefficient R=0.92) was found, in spite of that $\sim$90% of the spacecraft data used in the fitting were taken at synchronous orbit and beyond, while only 3.7% of those data came from distances $2.5\le R\le4\,R_E$. The obtained results demonstrate the possibility to develop a dynamical model of the magnetic field, based on magnetospheric and interplanetary data and allowing one to reproduce and forecast the entire process of a geomagnetic storm, as it unfolds in time and space. Reference: N. A. Tsyganenko, H. J. Singer, J. C. Kasper, Storm-time distortion of the inner magnetosphere: How severe can it get ? J. Geophys. Res., v. 108(A5), 1209, 2003.
SM13A-1197 1340h
New Observations of the Non-Thermal Continuum Radiation at the Plasmapause
The non-thermal continuum radiation is an electromagnetic emission associated with the plasmapause and is an important feature of the coupled inner magnetosphere. It is now believed that there are three main types of non-thermal continuum radiation that are distinguished by their frequency range and source location. The normal continuum radiation (also referred to as the trapped and escaping continuum) is typically in the 5 to 100 kHz frequency range. The continuum enhancement is observed from 10-100 kHz frequency range coming from night-side source regions. Kilometric continuum is observed to be generated at the plasmapause, in the magnetic equator, deep in notch structures of the plasmasphere over a frequency range from 100 to 800 kHz. New observations of the normal non-thermal continuum from the IMAGE/RPI instrument show a distinct "Christmas-tree" pattern in the frequency-time spectrogram that extend from 10's of Hz into the kilometric continuum frequency range (300 kHz). These observations show source region at nearly all local times. New observations of the continuum enhancement shows that the emission is associated with night-side electron injections and results in a very broad emission cone extending in frequency up to 300 kHz. These new observations of NTC will be put in the context of their role in the coupling of the hot and cold plasma populations at the plasmapause as an inner magnetospheric response to geomagnetic storms.
SM13A-1198 1340h
Modeling of Radiation Belts Dynamics - Development of time dependent model and comparison with satellite data -
Drastic changes of the relativistic electron population in the radiation belt during magnetic storms have been observed for many years. Typically, the relativistic electron flux decreases during the main phase of the storm, and then recovers and increases from late main phase to the recovery phase. Although many mechanisms for flux variation including both adiabatic and non-adiabatic process have been proposed, identification of the dominant process is difficult because many physical processes occur simultaneously. Thus, the development of the dynamical model based on physical processes is necessary for quantitative understanding of the radiation belts. In order to investigate physical processes in the radiation belts, we develop 1D, time-dependent, physical model for the radiation belts. In the model, we solve the Fokker-Planck equation for radial diffusion. Several loss processes such as wave-particle interactions and Coulomb collisions inside plasmasphere and strong diffusion and EMIC/chorus loss outside plasmasphere are included as life times. The model can calculate time variation of the radiation belts using time-dependent radial diffusion coefficient and the data from SOPA instrument on the geosynchronous LANL satellites as the outer boundary conditions. The energy spectrum data derived from SOPA instrument are parameterized by relativistic double Maxwellian. Firstly, we reproduced the equilibrium structure of the radiation belts; inner belt, slot region, and outer belt. Next, we calculate time variation of the radiation belts and compare with data of JAXA/MDS-1 (Tsubasa) satellite. From 2002 to 2003, the MDS-1 satellite measured the energetic electron distribution with geosynchronous transfer orbit, and we can discuss temporal and spatial variation together with spectrum hardness of relativistic electrons for all regions of the radiation belts. In order to evaluate the variation of the outer boundary condition and time dependent radial diffusion coefficient, we perform numerical experiment with varying parameters in the model. As an initial result, the time dependent boundary condition is important for the flux decrease during the main phase and increase in the outer portion. However, the time dependent boundary condition does not affect the variation of the inner portion. On the other hand, the time dependent radial diffusion coefficient is effective for flux variation of slot region and inner portion of the outer belt. Furthermore, it is reveled that the simulated flux is smaller than the observed. It is expected that further processes such as internal process is necessary in the outer radiation belt.
SM13A-1199 1340h
Global Proton Pressure Distributions in the Inner Magnetosphere Derived by IMAGE/HENA Using Realistic Magnetic Fields and Their Relation to Birkeland Currents Measured by Iridium
Comparisons between IMAGE/HENA derived proton pressure-driven Birkeland currents and Iridium observations at ionospheric altitudes have shown that the IMAGE/HENA inversions currents are sensitive to the magnetic field used in the HENA inversion. This motivated improving the HENA inversion technique by using the latest Tsyganenko magnetic field model which was upgraded to represent storm-time effects in the inner magnetosphere. We present results using this new inversion. Since the retrieved proton fluxes are in the 10-200 keV range, we can only calculate the partial plasma pressure, about 60 percent of the total pressure, in the inner magnetosphere. We then calculate the electrical currents associated with that pressure distribution via the force balance equation (using the same Tsyganenko field model). The HENA proton pressures are compared against in-situ satellite observations as a cross check on the inversion. The more stringent test of the inversion is provided by comparing the Birkeland currents calculated from the HENA data against those derived from the magnetometer data obtained from the Iridium satellites. This inter-comparison not only allows us to validate the HENA inversions but also to shed light on the contribution of the proton pressure to the total current system and how this contribution depends on solar wind and magnetospheric conditions.
SM13A-1200 1340h
Simulation Study of the Inner Magnetosphere for May 2-6, 1998
Using the University of Michigan`s BATS-R-US MHD Model to drive the Fok Radiation Belt and Ring Current Models, we will examine the relative importance of different mechanisms for energy gains and flux enhancements for the inner magnetosphere during the May 2-6, 1998 storm. The global model provides the magnetic and electric fields for the inner magnetospheric models. The inner magnetospheric models solve the bounce-averaged distribution function for protons and electrons including terms for diffusion, convection, and loss processes. In particular we will examine how energy diffusion in the radiation belt model impacts flux enhancements during the recovery stage. We will also investigate how different mechanisms in the ring current model impact the rapid recovery on May 4. We will compare the results of the radiation belt and ring current models to LANL geosynchronous data to validate the results of the models.
SM13A-1201 1340h
A Statistical Study of Intense High-Altitude Electric Fields Using Cluster
The occurrence and characteristics of intense ($\geq$150 mV/m, mapped to the ionosphere) electric fields at high altitudes (4-7 R$_{E}$) are investigated in a statistical study using data from the Cluster satellites. The 36 months of EFW data used from four satellites give a good database for statistical interpretations. The relation of the events to MLT, Ilat, altitude and other parameters are investigated. An attempt to distinguish between divergent and convergent potential structures is made. The relation of the intense electric field events and up- and down-going currents is analyzed. Although the satellites at this stage in the investigation are considered as single point measurements, the possibilities of a four-point statistic are tempting.
SM13A-1202 1340h
LFM meets RCM: Initial results of two-way coupling
As part of the space environment modeling activities of the Center for Integrated Space Weather Modeling (CISM), we have been developing a coupled model that merges the Rice Convection Model (RCM) of the inner magnetospheric model with the Lyon-Fedder-Mobary (LFM) global MHD model of the magnetosphere. We present preliminary results from the coupled code where the LFM provides magnetic and electric fields, ionospheric conductivities, and plasma distributions to the RCM; the RCM then returns to the LFM updated plasma quantities. Using results from the coupled code with idealized inputs and varied coupling algorithms, we discuss the inner magnetosphere effects of this coupled model, such as the formation of region-2 field aligned currents, electric field shielding and ring current formation, as well as the response of the global magnetosphere, such as the magnetic field and cross polar cap potential.
SM13A-1203 1340h
Radial Diffusion Modeling with Data Derived Effective Lifetimes: Losses Inside and Outside Plasmasphere
We attempted to quantify the competing effects of inward radial diffusion and losses inside and outside plasmasphere on the distribution of the outer zone electrons with a time dependent radial diffusion model. We present a detailed analysis of individual storms as well as comparison of data and model for 500 CRRES orbits. The rate of radial diffusion has been parameterized by the Kp with the loss time as an adjustable parameter. We find that plasmapause is a boundary between rapid and moderate losses. 1.0 MeV electron lifetimes are less then 1/2 day during the storm main phase and 3 days under quiet conditions, consistent with current estimates of the storm time loss rate [Albert, 2003; Summers and Thorne, 2003; O'Brien et al., 2003] and also provide an acceptable representation of electron decay rates following the storm time injection. We find that a radial diffusion source alone with data derived effective lifetimes approximately reproduces the amplitude and spatial distribution of outer zone fluxes, but fails to reproduce the gradual build up of fluxes observed for many storms as well as depletions of the radiation belts during the main phase of the storm. This suggests the need to include the local acceleration source as well as local loss which could be estimated from the comparison of the model results with fluxes derived in terms of Roederer L* using various field models .
SM13A-1204 1340h
Inner magnetosphere results from April 2001 coupled model runs
The Michigan Space Weather Modeling Framework (SWMF) has been developed to facilitate coupling models from various domains. The SWMF is used here to couple models of the global magnetosphere (BATSRUS), ionosphere, thermosphere (GITM), and inner magnetosphere (RCM) for the focus storm period of April 2001. We will show the effects of coupling the models, and compare with available observations. We will highlight the global three dimensional nature of processes during the event, including the evolution of the ring current and global current patterns.
SM13A-1205 1340h
Statistical distribution of ring current ions observed by NOAA/POES satellites
The dynamics of the ring current ions are studied in detail by using the observations of the NOAA/POES satellites (N15, N16, N17) from 2001 until now. These satellites observe energetic (keV - MeV) particles at altitudes of about 800 km and across the magnetic footprint of the ring current region. The orbit of three satellites can cover all magnetic local times (MLT) during a storm event. From the two-dimensional statistical analysis, we have confirmed that the ring current ions observed by the P0 (30-80 keV) channel show asymmetric distribution. The time variation of the ion flux during magnetic storm appears as intensity and special variation. Intensity of the ion flux shows MLT asymmetry; strongest in the pre-midnight sector (20-24 MLT). The flux in the post-midnight sector (0-4 MLT) tends to intense rather than that in the dusk sector (16-20 MLT). In comparison with the post-midnight sectors, the flux enhancement is very weak in the dawn and pre-noon sector (4-8 and 8-12 MLT) during storm times. The timing of ion flux enhancement during storm time is typically as the following: the ions in the pre-midnight sector increase firstly (in the initial phase) at about L = 6 and those in the post-noon sector increase finally (in the main phase). In the main phase, the peak flux of the ions is at about L = 4. In the recovery phase the ion fluxes in the all sectors decrease while these latitudes (L-values) increase. However, such asymmetric distribution still remains after the storm event. Even during non-storm period, the ring current ions exist in the pre-midnight and its neighbor sectors at L = 5 to 7. Only during Kp $<$ 1 (very quiet period) such asymmetry disappears. This suggests that substorm injection play a role of ion distribution during non-storm time. The relationship between asymmetry of ring current ions and that of magnetic field variations observed on the ground will be discussed in this presentation.