SM41A-1101 0800h
Radiation Belt Modeling and Data Assimilation with Salammbo
The dynamic processes in the radiation belt, especially relativistic electron acceleration and transport, are not fully understood. Currently, neither data-based statistical models nor physics based models alone can capture all of the observed dynamics. Here, we combine the extensive observational data of energetic electrons in the inner magnetosphere with a physical model of transport processes in the radiation belt using the diffusion code Salammbo. Initial data comes from the LANL GEO and GPS constellation and Polar. Based on data assimilation methods of numerical weather prediction (nudging, Cressman analysis, successive correction method, Kalman filter), the information from measurements is propagated not only in time but also in space into so-called data voids or holes. We present here details and problems about data assimilation methods as applied to sparse space physics data and discuss the results we obtained.
SM41A-1102 0800h
Preliminary Simulation Results for Stormtime Ring Current in a Self-Consistent Magnetic Field Model
The stormtime ring current generates a strong and time-dependent perturbation of the magnetospheric $\vec{B}$ field, and this magnetic-field perturbation can have important feedback on the dynamics of ring current particles themselves. In particular, the modification of $\vec{B}$ can significantly alter the gradient-curvature drifts of ring current particles, and the induced electric field associated with $\partial\vec{B}/\partial t$ can inhibit ring current particle injection and energization. Thus, in order to accurately simulate the stormtime ring current, we need a self-consistent magnetic field model that takes into account effects of the ring current on the particles that produce it. This study is our first attempt to address this issue. We assume for simplicity a model for $\vec{B}$ ($= \nabla\alpha\times\nabla\beta$) such that magnetic field lines lie in meridional planes and satisfy the generic equation $r = La(1+0.5r^3/b^3)\sin^2\theta$, where $r$ is the radial distance from the point dipole, $\theta$ is the magnetic colatitude, $a$ is the radius of the Earth, $L$ is a dimensionless field-line label inversely proportional to the Euler potential $\alpha = -\mu_E/La$, $\beta$ is the magnetic local time, and the parameter $b$ (a function of $L$ and $\beta$) controls the amount by which a field line is stretched. The special case of constant $b$ yields Dungey's model magnetosphere (dipole field plus uniform southward $\Delta B$), in which the limit $b\rightarrow\infty$ corresponds to a purely dipolar $B$ field ($\Delta B = 0$). More generally, we now let the value of $b$ varies from field line to field line so as to account also for the ring current's contribution to equatorial $\Delta B$ as a function of $r$ and $\beta$. The self-consistent magnetic field should satisfy the force balance, as specified by the equation $\mu_0^{-1}\vec{B}\times(\nabla\times\vec{B}) = -\nabla\cdot\vec{\vec{P}}$, where $\mu_0$ is the permeability of free space and $\vec{\vec{P}}$ is the pressure tensor. Under these assumptions, the radial component of the left-hand side of the force balance equation in the equatorial plane can be expressed via an ordinary differential equation in $L$ or in $r_0$, where $r_0$ is the geocentric radial distance in the equatorial plane (related to $L$ by solving the equation of a field line for $r$ at $\theta = \pi/2$). Given the plasma pressure in the equatorial plane as a function of $r_0$ and $\beta$ as a result of our bounce-averaged guiding center simulations of representative ring-current particles, we can thus solve the pressure-balance equation to obtain the self-consistent magnetic field. We will show some preliminary results found by applying this method to actual ring-current plasma simulations.
SM41A-1103 0800h
Correlation Between Particle Injections Observed at Geosynchronous Orbit and the Dst Index During Geomagnetic Storms
To understand the relationship between geomagnetic storms and substorms, we examine the correlation between dispersionless proton injections observed by geosynchronous satellites and the Dst index during geomagnetic storms. We utilize geomagnetic storms occurred during the period of 1997$-$2002, categorizing them into four classes according to the minimum Dst value, Dst$_{min}$; Severe (Dst$_{min}$$ <$ $-$200 nT), intense ($-$200 nT $\leq$ Dst$_{min}$$ <$$-$100 nT), moderate ($-$100 nT $\leq$ Dst$_{min}$$ <$$-$50 nT), and weak ($-$50 nT $\leq$ Dst$_{min}$$ <$$-$30 nT) storms. We use the proton flux with the energy range from 50 keV to 670 keV observed by the LANL geosynchronous satellites located in the dark hemisphere from 1800 LT to 0600 LT. It is not possible to deduce the amount of the total energy injection into the inner magnetosphere from measurements only by one or two satellites. Nonetheless, we may obtain a quantity that is proportional to the true injection rate during magnetic storms by estimating the flux increase expressed in terms of the flux ratio (f$_{max}$/f$_{pre\_ave}$) and the number of injections, where f$_{pre\_ave}$ and f$_{max}$ represent the average flux of pre-storm level and onset level, respectively. Thus, we propose to introduce a parameter, >total energy injection parameter (TEIP)>', defined by the product of the flux ratio and the number of injections, as an indicator of the energy injected into the inner magnetosphere. To determine the phase dependence of the substorm contribution to the development of geomagnetic storm, we examine this quantity for the main and recovery phases separately. Several interesting points are noted particularly for the main phase of storms. First, the number of particle injections tends to increase with the storm size. Second, the flux ratio (f$_{max}$/f$_{pre\_ave}$) also tends to increase with the storm size. The correlation coefficient between Dst$_{min}$ and the flux ratio is high, for example, 0.84 for the 50$\sim$75 keV energy channel. Third, there is also a significantly high correlation between TEIP and Dst$_{min}$. Particularly, the correlation coefficients are very high, above 0.85, for those channels of energy, 50$\sim$400 keV, which represent the typical energy range of ring current particles. These results indicate that the substorm expansion activity is higher during the main phase than the recovery phase, suggesting that the substorm expansion activity seems to be closely associated with the development of magnetic storms. Fourth, particle injections during the recovery phase of a storm tend to make the storm last longer. This tendency is particularly prominent for more intense storms.
SM41A-1104 0800h
Solar Wind Dynamic Pressure during Magnetic Storms and Its Implications on the Dayside Ring Current Particle Loss
It has been known that (untrapped) ring current particles can be lost through the dayside MP(magnetopause) into the magnetosheath. However, details of the loss mechanism of this process have not received much attention. In this paper, we show that the solar wind dynamic pressure can play a significant role in the dayside loss. In order to show that, we have first analyzed the average characteristics of the 95 geomagnetic storm events selected from the period 1997 to 2002. We find that the dynamic pressure overall enhances during the magnetic storm. The enhancement is most significant during the storm main phase and it is higher for stronger storms. Using one of the most recent Tsyganenko models, T01_s, we show that this enhanced dynamic pressure not only pushes MP to move inward but also sets an enhanced gradient of the magnetic field intensity along the MP. On the basis of the test particle calculation, we explicitly show that the increased gradient of the magnetic field intensity along the MP can be a significant factor for the particles to effectively cross the MP by the gradient-drift. We argue that this can often apply to the majority of the ring current particles.
SM41A-1105 0800h
A Multiple Balloon Campaign to Study Relativistic Electron Loss Mechanisms
The MINIS balloon campaign will be conducted in January 2005 to investigate relativistic electron loss mechanisms. Quantifying and understanding losses is an integral part of understanding the variability of relativistic electrons in the radiation belts. Balloon-based experiments directly measure precipitation and thus provide a method for quantifying losses, while the nearly stationary platform allows for the separation of temporal and spatial variations. The MINIS campaign will provide the first multi-point measurements of electron precipitation up to MeV energies, including simultaneous measurements at different longitudes and at conjugate locations. We will also obtain the first correlated optical and MeV X-ray observations. Two balloons, each carrying an X-ray spectrometer for measuring the bremsstrahlung produced as electrons precipitate into the atmosphere, and an H-beta photometer to detect correlated proton precipitation, will be launched from Churchill, Manitoba. Four balloons, each carrying an X-ray spectrometer, a Z-axis searchcoil magnetometer, and a 3-axis electric field instrument providing DC electric field and VLF measurements in 3 frequency bands, will be launched from the South African Antarctic Station (SANAE). Each payload will be carried to 120,000 ft ($\sim$35 km) on a 300,000 cubic foot balloon; the northern payloads will remain aloft for 1-2 days covering L-values 4.5-7.8 while the southern balloons will stay at float altitude for about 8 days, ranging from L$\sim$4 into the polar cap. We will investigate whether EMIC waves are responsible for scattering relativistic electrons, will distinguish between drift loss cone and bounce loss cone precipitation, and will measure the longitudnal extent of precipitation. GPS will provide accurate time synchronization of conjugate payloads, allowing us to conduct a careful timing analysis of microbursts at conjugate locations. An Iridium satellite modem will allow us to receive continuous real-time data from each payload. In this paper, we present an overview of the campaign, including a description of the instrumentation and launch plan.
SM41A-1106 0800h
A Remarkable Energetic Electron Event In Late July 2004
Beginning late on Day 204 (2004) ACE observed a solar wind speed of almost 700 km/sec and Bz strongly southward for many hours. The trapped energetic electron population (~ 1 MeV) showed a strong increase, peaked near L = 4 and with a lower edge just outside of L=3. Late on Day 207 the solar wind speed again approached 700 km/sec and again Bz was strongly south. The energetic electrons responded again, with the intense population reaching down to L=2.4. Then on the beginning of Day 209, the solar wind velocity went to 1000 km/sec with Bz strongly south for a third time. The entire outer zone filled with energetic electrons from L=2 to GEO. HEO observations of the entire outer zone showed the most intense population of energetic electrons since the launch of 1994-026 in the Spring of 1994. The energy spectrum also was very hard. In addition the GEO population of > 2 MeV electrons were higher than had been observed since at least 1986. These and other observations will be discussed and compared with the observations made during the remarkable series of events in October-October-November 2003.
SM41A-1107 0800h
Drift-Shell Bifurcation
Certain drift shells that pass sufficiently close to the dayside magnetosphere encounter a local maximum around the equatorial plane, and near local noon. As a result of that local maximum, the shell undergoes a bifurcation, with one branch in each hemisphere. Past the neighborhood of local noon, the branches meet again. The line where bifurcation occurs is a singular line, where the bounce period goes to infinity. As a result, the adiabaticity of the bounce motion breaks down and the post-bifurcation second invariant can be significantly different from the initial value. The first invariant is not broken. We provide simulations, and an analysis in terms of the "separatrix crossing" theory. The change in the second invariant is stronger with small mirror field, with small initial second invariant and with large kinetic energy. Also, bifurcation has the effect of creating "metastable shells", by keeping quasi-trapped particles inside the magnetosphere for a finite number of drifts.
SM41A-1108 0800h
Solar Energetic Particle Entry and Trapping in the Magnetosphere During Geomagnetic Storms
We investigate numerically the relationship between geomagnetic cutoff and the prompt trapping of Solar Energetic Particles (SEPs) in the inner magnetosphere during storms, which form new radiation belt populations distinct from the cosmic ray albedo neutron decay (CRAND) source protons in the inner zone. SEP cutoffs are modeled using the Lyon-Feder-Mobarry (LFM) global magnetosphere MHD code, which is driven by measured solar wind parameters at the sunward boundary. In a follow up to our recent paper [Kress et al., 2004], we further study SEP trajectories in fields from the 24 NOV 2001 LFM storm simulation. By mapping surfaces of constant cutoff rigidity in the LFM fields, we show that SEPs with access to the innermost L shells enter through the magnetopause on the day side and predominately in the magnetic equatorial plane. It is found that a significantly compressed magnetopause has a profound effect on the asymmetry of the cutoff surface suggesting a mechanism for SEP trapping.
SM41A-1109 0800h
Characterizing Relativistic Electrons Flux Enhancement Events using sensors onboard SAMPEX and POLAR
Relativistic electron fluxes in the Earth's outer Van Allen belt are highly variable with flux enhancements of several orders of magnitude occurring on time scales of a few days. Radiation belt electrons often are energized to relativistic energies when the magnetosphere is subjected to high solar wind speed and the southward turning of the interplanetary magnetic field. Characterization of electron acceleration properties such as electron spectra and flux isotropization are important in understanding acceleration models. We use sensors onboard SAMPEX and POLAR to measure and survey systematically these properties. SAMPEX measurements cover the entire outer zone for more than a decade from mid 1992 to mid 2004 and POLAR covers the time period from mid 1996 to the present. We use the pulse height analyzed data from the PET detector onboard SAMPEX to measure electron spectra. Fluxes measured by the HIST detector onboard POLAR together with the PET measurements are used to characterize isotropization times. This paper presents electron spectra and isotropization time scales for a few representative events. We will eventually extend these measurements and survey the entire solar cycle 23.
SM41A-1110 0800h
The Halloween 2003 Storm's Effect on Trapped Electron Populations
We have investigated the effects of the October and November 2003 solar energetic particle (SEP) events on trapped electron populations using data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) in conjunction with the findings from the Solar, Anomalous, Magnetospheric Particle Explorer (SAMPEX). Immediately after the Halloween storm, RHESSI, saw an order of magnitude increase in the electron population in its low particle energy bin (less than 600 KeV); the population lingered for more than thirty days at L=1.9-2.2. The increase is caused by an inward transportation of trapped magnetospheric electrons from higher L values, and the decay is produced by pitch angle diffusion. Similar effects were seen by SAMPEX. However, the appearance of SEP's, whose energies are much greater and range up to 20 MeV, does not occur until months later, as these electrons are not pitch angle diffused as quickly as the lower energy population.
SM41A-1111 0800h
A case study of relativistic electron events for their relationship to substorm injections and ULF powers
We study the two storm events of 1997: the one in May that accompanied a relativistic electron event (REE) and the other in September which, with a more profound Dst decrease, showed no significant flux increase of relativistic electrons. We find a larger amount of seed electrons is present in the May event compared to that of the September storm while the ULF power is more enhanced and the particle spectrum harder in the September event. Hence, we demonstrate that a larger storm does not necessarily produce more seed electrons and the amount of seed electrons is an important factor of an apparent increase in REE flux levels, while ULF can harden particle spectra without causing an apparent REE.
SM41A-1112 0800h
Remote Sensing of Relativistic Electron Precipitation Using a VLF Beacon Transmitter at South Pole
The Stanford University VLF beacon transmitter located at South Pole has been operating at 19.4 kHz continuously since November 2003. The main utility of the beacon is to serve as a tool for continuously monitoring the effects of relativistic particle precipitation on the D-region of the ionosphere in the auroral regions of the Southern Hemisphere/Antarctica. We present data from the first year of operation, showing VLF beacon signal amplitude and phase as received at Palmer and discuss its characteristics and variations due to diurnal and seasonal effects. The months from April to August are ideal for the beacon observations due to the fact that the VLF great circle path from South Pole to Palmer experiences extended periods of darkness and is thus sensitively disposed to the ionospheric effects of relativistic electron precipitation. We focus our discussion of the VLF data to two periods of high geomagnetic activity, one in April and one in July of 2004. The VLF beacon data are compared directly with energetic particle fluxes measured with the PET-ELo instrument on the SAMPEX sattelite during these same periods. The fluxes observed on SAMPEX are used to generate profiles of ionospheric density in regions along the great circle paths from South Pole to Palmer and a quantitative model of Earth-ionosphere waveguide propagation is used to interpret the observed VLF amplitude and phase changes in terms of relativistic electron flux enhancements.
SM41A-1113 0800h
Analysis of the Variation of Energetic Electron Flux with Respect to Longitude and Distance Normal to the Magnetic Equatorial Plane for Galileo Energetic Particle Detector Data
In this study we examine ten-minute omni-directional averages of energetic electron data measured by the Galileo spacecraft Energetic Particle Detector (EPD). Count rates from electron channels B1, DC2, and DC3 are evaluated using a power law model to yield estimates of the differential electron fluxes from 1 MeV to 11 MeV at distances from the planet Jupiter from 8 to 28 Jupiter radii. Whereas the orbit of the Galileo spacecraft remained close to the rotational equatorial plane of Jupiter, the approximately 11 degree tilt of the magnetic axis of Jupiter relative to its rotational axis allowed the EPD instrument to sample high energy electrons at limited distances normal to the magnetic equatorial plane. We present a Fourier analysis of the semi-diurnal variation of electron radiation with longitude. We also develop a model of the electron flux with respect to distance normal to the magnetic equatorial plane as a function of the distance from Jupiter.
SM41A-1114 0800h
Radial Diffusion Coefficients for the Transport of Radiation-Belt Particles: a Case Study for Protons and Electrons in Jupiter's Inner Magnetosphere
We propose to discuss the general expression for the radial diffusion coefficients of energetic charged particles transported in magnetospheric systems. Since the late 60's and based on the postulate that diffusion only violates the particle's third adiabatic invariant, radial diffusion coefficients inside inner magnetospheres of the outer planets have been assumed to be driven by neutral winds in the ionosphere implying that $D_{LL} = D_{o}*L^{n}$ in parametric form. $D_{o}$ and n are free parameters usually constrained by observations. We will discuss the parameters n and Do, and the L dependence of such coefficients by reexamining a more rigorous expression of the radial diffusion coefficients. In a dipolar approximation, the expression for these coefficients is simple making it easier is to bring out their dependence as a function of the type of particle, energy, pitch-angle and radial distance. Consequently, the limits of validity of the general parametric form can be discussed. The radial diffusion coefficients used in the governing Fokker-Planck transport equation allow determination of the averaged radiation-belt particle populations by providing a balance between sources and losses. We then illustrate the consequences of the different expressions of the transport coefficients on the radiation belts of Jupiter. Furthermore, given the assumed origin of the particles' transport, the effects of the radial diffusion (including the solar-wind dynamic pressure, and the consequences of its fluctuations) can also be studied on the steady state radiation belts and implications for the long-term variations observed in Jupiter's synchrotron emissions evaluated.
SM41A-1115 0800h
Effect of Solar Wind Dynamic Pressure Enhancement on the Development of Ring Current Asymmetry
Our previous study has shown that solar wind dynamic pressure enhancement can further increase ring current asymmetry when it occurs during the main phase of a storm. We also found that pressure enhancement during the early recovery phase can slightly strengthen the asymmetry of a partially symmetric ring current, and that the pressure enhancement effect on ring current asymmetry is negligible during the late recovery phase. The effects therefore highly depend on storm phases and the state of the ring current at the time of the onset of a pressure enhancement. In this study, we statistically investigate the effect of a pressure enhancement on the ring current development under more general conditions, i.e. not necessarily occurring during a magnetic storm. We select pressure enhancement events occurring during the period of June 2003 to December 2003, during which we have magnetometer observations from the SAMBA and 210 chains, located approximately 180 degrees in longitude apart. Through examining the variations in the H and D components of the geomagnetic in those events, it is preliminarily found that pressure enhancements have significantly smaller effect on the development of ring current asymmetry during non-storm time than during storm time. The results also show that the orientation of IMF Bz plays a very important role in influencing ring current asymmetry during non-storm time, the effect being stronger for southward IMF Bz than for northward IMF Bz.
SM41A-1116 0800h
Characteristics of Ion Outflow Near the Auroral Zones
We have performed a large statistical survey of the net upward flux of ions from the auroral ionosphere, using data from the electrostatic analyzer aboard the FAST mission. Measurements of ions from 0.05- 30 keV, at all pitch angles simultaneously and with redundancy, are integrated to give measurements of the net flux. The flux data are binned according to 3 ancillary and 3 intrinsic properties. The ancillary properties are (1) location relative to the auroral zone, (2) concurrent interplanetary magnetic field condition, (3) ionospheric illumination at the 100 km footpoint of the corresponding flux tube. The intrinsic properties are (1) distribution type, (2) intensity, and (3) the characteristic energy. We use a dynamic coordinate, based on the instantaneous latitudinal location and width of the auroral zone, as defined by precipitating electron flux. Doing so allows us to resolve spatial features (in synoptic averages) which would otherwise be obscured by the variation (with auroral activity) in the latitude of the auroral zone. Binning the data according to outflow intensity shows that most of the ions leaving the ionosphere do so as part of relatively rare and intense ($> 10^{8}$ cm$^{-2}$-sr$^{-1}$-s$^{-1}$) beam-like events. The relative significance of beam-like and conic distributions will be compared at different locations and under various geophysical conditions.
SM41A-1117 0800h
Imaging Time-of-Flight Ion Mass Spectrograph
Identification of the ion constituents in space plasmas provides important clues to understanding their structure and dynamics and unraveling thecomplex interactions that occur across plasma boundaries, such as the interaction between the solar wind and the Earth's magnetosphere. We present results from a proof-of-concept time-of-flight ion mass spectrograph. This ungated spectrograph electrostatically rasters a continuous ion beam at the entrance of a drift tube and detects the position of the ions at the end of the drift tube. The ion speeds, energy-per-charge ratios, and mass-per-charge ratios can be determined simultaneously for a wide range of ion masses. Spectra were taken with multiple simultaneous species and energies-per-charge.
SM41A-1118 0800h
Effects of magnetic field asymmetry and compressional magnetic perturbations on radial diffusion of radiation belt electrons
The radial diffusion coefficient of particles in a symmetric magnetic field perturbed by fluctuating electric fields is well known to depend on the power spectral density of the electric field at frequencies $\omega = m \omega_d$ (where $m$ is the azimuthal mode number, $\omega_d$ is the particle drift frequency) with an $L^6$ factor. In this work we have derived a radial diffusion coefficient for particles in an asymmetric magnetic field. The asymmetric diffusion coefficient depends on electric field power at resonance frequencies $\omega = (m \pm 1) \omega_d$ with $L^{12}$ dependence multiplying the power spectral density. Numerical diffusion rates obtained using test-particle simulations in model fields agree well with the analytical diffusion coefficients. Solutions of the radial diffusion equation for the September 1998 storm event are compared to an MHD-particle simulation. Earlier calculations used only electric-field diffusion coefficients, which had to be increased by a factor of 2 to 3 to get the best match with the MHD-particle results. New results will be presented of a radial diffusion calculation with compressional ULF waves added.
SM41A-1119 0800h
Energetic Ions in the Magnetosphere during a Magnetic Storm
The magnetic storm of November 24, 2001 was characterized by an increase in the energetic ion flux in the solar wind by more than an order of magnitude over a wide energy range, and accompanied by the arrival of interplanetary shocks. Large increases in ion flux were observed by geosynchronous spacecraft, which was followed later by a substantial drop in DST. The shocks were accompanied by large increases in the dynamic pressure. Both solar energetic particle (SEP) penetration and accelerated solar wind ions contributed to the energetic particle population in the magnetosphere. To study the entry and acceleration processes we performed particle tracing calculations in the electric and magnetic fields from a global magnetohydrodynamic (MHD) simulation. We performed an MHD simulation of this storm interval by using solar wind and IMF time series measured by upstream spacecraft which determine the upstream boundary conditions for the MHD simulation. Particle trapping increased greatly after the passage of the interplanetary shocks and ions were energized as these shocks interacted with the Earth's bow shock and magnetosphere.
SM41A-1120 0800h
Measurement of the Energetic Ion Population With the Medium Energetic Neutral Atom (MENA) Imager
The Medium Energy Neutral Atom (MENA) imager, launched aboard the IMAGE spacecraft in 2000, was designed to perform remote sensing of the 1-70 keV ring current by measuring Energetic Neutral Atoms (ENAs). To isolate the remote-origin ENAs from the local plasma, a series of collimator plates are used to reject charged particles from entering the imager. The alternate collimator plates have high voltage applied to sweep out charged particles. The cut off energy for the charged particles is a function of the voltage applied to the collimator plates. The MENA collimator plates have been run at a reduced voltage, allowing energetic ($>$35 keV) ions to enter into the imager. For most of the mission, the signal from the entry of charged particles into the instrument is at levels of at least an order of magnitude below the ENA signal. However, there are times when high background (non-ENA) events are seen. At these times, the background flux can be significant when compared to the ENA signal. This elevated background has been observed during all times of the orbit while MENA is operational (L-shells $>$ 9) and for all spin phases of the spacecraft. The background levels are higher on the dayside than on the night side. We present conclusive evidence that the MENA instrument's elevated background is from energetic charged particles passing through the collimators. The intensity of this charged particle flux into MENA is seen to correlate well with the energetic particle sensor (0.7 to 4 MeV) on the GOES-8 satellite. They also correlate well with changes in Dst and with solar wind dynamic pressure. Since the flux of ENAs is relatively weak, a large geometric factor was required in MENA. Therefore, MENA can play a dual role in observing geospace. During low-background conditions, MENA provides global images of the ring current plasma distribution. When high background signals exist, MENA can also serve as a sensitive, useful detector of the in situ plasma environment.
SM41A-1121 0800h
A genetic programming approach for time-series analysis and prediction in space physics.
A central theme in space weather prediction is the ability to predict time-series of relevant quantities, both empirically, and from physics-based models. Empirical models are often based on educated guesses, or intuition. The task of finding an empirical relationship relating quantities can be tedious and time-consuming, especially when a large number of parameters are involved. Genetic Programming (GP) provides a method for automating the guesswork, and can in some instances automatically find functional relationships between data streams. GP is an evolutionary computation technique which is an extension of the Genetic Algorithm framework used for function optimization. In GP an evolutionary algorithm combines elementary function operators in an attempt to build a function which is able to reproduce a training example from a set of input data. We will illustrate how a GP algorithm can be used in space physics by addressing two relevant topics: The prediction of relativistic electron fluxes, and prediction of $Dst$.
SM41A-1122 0800h
Recent analysis of magnetic field and beta particle measurements of the Starfish nuclear burst plasma expansion and collapse.
Five spacecraft located 100 to 1000 kilometers around the Starfish nuclear burst measured the expansion and collapse of the plasma bubble produced in the geomagnetic field and early time injection into the inner Van Allen radiation belt. The bubble evolved into an elongated shape 2400 km along the magnetic field lines and 700 km across in 1.2 seconds and required approximately 15 seconds to collapse. After the magnetic bubble reached its maximum size instabilities and fluting permitted the beta emitting fission fragments to continue to expand. This process injected a flux measuring 2.5x1010 beta/cm2sec into the most intense region of the artificial belt mapped by the Injun I spacecraft 10 hours later.
SM41A-1123 0800h
Estimates Of Radiation Belt Remediation Requirements
A low-Earth orbit nuclear detonation could produce an intense artificial radiation belt of relativistic electrons. Many satellites would be destroyed within a few weeks. We present here simple estimates of radiation belt remediation by several different techniques, including electron absorption by gas release, pitch angle scattering by steady electric and magnetic fields from tether arrays, and pitch angle scattering by wave-particle interactions from in-situ transmitters. For each technique, the mass, size, and power requirements are estimated for a one-week remediation (e-folding) timescale, assuming that a 10 kTon blast trapped 1024 fission product electrons (1 to 8 MeV) at L = 1.5 in a dipolar belt of width dL = 0.1.
SM41A-1124 0800h
Transforming Away the Cross Term in Quasilinear Diffusion
Two dimensional quasilinear diffusion can play an important role in wave-particle interactions, e.g. in stormtime acceleration of electrons. The appropriate diffusion coefficients have been calculated, but time-dependent solution of the diffusion equation is numerically difficult because of the often large and rapidly varying cross term. Transforming to variables aligned with the eigenvectors of the diffusion matrix leads the cross term to vanish, which is a large physical, mathematical, and numerical simplification. Details of the transformation and physical interpretation will be presented, along with application to a model problem.
SM41A-1125 0800h
The impact of ULF waves on radiation belt electrons
During geomagnetic storms relativistic electrons in the Earth's outer radiation belt exhibit highly variable and complex behavior and understanding their dynamics is one of the fundamental questions of contemporary space physics. Previous studies show that one of the primary mechanisms of electron transport and acceleration is radial diffusion induced by wave-particle interaction with ULF waves in the inner magnetosphere. However, there is no consensus about what the diffusion rates are, how they depend on the level of geomagnetic activity or the relative role of diffusion in overall particle dynamics. In this paper we investigate the impact of the inner magnetospheric ULF waves on the outer radiation belt electrons. The study involves theory, data analysis and numerical simulations. We use electromagnetic fields measured by elliptically orbiting CRRES spacecraft to investigate the spatial and temporal development of storm time ULF waves. Acquired wave fields are used to calculate diffusion rates during disturbed geomagnetic conditions and compare them with theoretical estimates.
SM41A-1126 0800h
Evolving Phase Space Density Distribution of Relativistic Electrons in Storm Times
Understanding the behavior of relativistic electrons in the Earth's radiation belts in geomagnetic storm times is a critical prerequisite for space weather prediction. Intensive efforts have been made to describe the relativistic electrons dynamics in storm times and some competing theories and models have been developed. However, the differentiation of those models requests extensive comparisons with in-situ data. To fulfill it, this study will conduct a survey of the temporal evolving phase space density (PSD) distribution of relativistic electrons in storm periods. Data used in this work include electron and magnetic field measurements from multiple spacecraft, which are the LANL GEO satellites, GOES satellites, POLAR and CLUSTER. With orbits going through all key inner magnetospheric areas, those satellites form a constellation which provides simultaneous measurements at multiple locations so that spatial factor can be easily separated from temporal one. Additionally, the fact that detected electrons have a wide range of adiabatic invariants, covering both equatorially and off-equatorially bounded ones and L*~2-9, allows tracing a specified electron population across the adiabatic phase space. The calculation of PSD in quiet times is first implemented for the inter-satellite calibration. Thereafter the PSD in storm periods can be deduced based on the optimized magnetospheric magnetic field model developed in previous study. To constrain the errors in the PSD calculation, the Liouville's Theorem is employed to check the reliabilities of calibration and magnetic field in both steps. This work will establish the radial PSD gradient as a function of both universal time and local time, which can serve later as the reference of differentiating physics processes associated with acceleration and loss of relativistic electron during storm phases.
SM41A-1127 0800h
Acceleration of Relativistic Electrons Through Whistler Mode Instability Driven by Temperature Anisotropy
The resonant scattering process via whistler mode waves has been recognized as the strong candidate mechanism for the acceleration process of relativistic electrons during the recovery phase of a geomagnetic storm in the inner magnetosphere. We study resonant interaction between relativistic electrons and monochromatic whistler mode waves by using a self-consistent simulation model. The simulation model is based on the model which treats background cold electrons as a fluid and hot electrons as particles by PIC method including fully relativistic effect. In the simulation system, oppositely traveling monochromatic whistler mode waves are excited by an instability associated with a temperature anisotropy of keV energy electrons. The simulation result shows that the energy transfer process takes place between relativistic electrons and keV electrons and that the monochromatic whistler mode wave traps relativistic electrons which satisfy the resonance condition. Especially, in a case that oppositely propagating monochromatic waves coexist, a combined effect of wave trapping connects diffusion curves and opens a route for the rapid acceleration. The motion of the trapped relativistic electrons in the momentum space is estimated from the intersection of resonance curves and the scale of trapping region which is determined by both trapping velocity and resonance velocity. The present simulation reveals that selected resonant electrons are effectively accelerated in a homogeneous system where both forward and backward traveling waves interact with the relativistic electrons.
SM41A-1128 0800h
Comparison of MeV Electron Response During the October-November 2003 and July 2004 Storm Intervals
A comparison of the MeV electron response during the October-November 2003 and July 2004 storm intervals is made using data from the Air Force Research Laboratory Compact Environmental Anomaly Sensor (CEASE) flying in low Earth orbit on the TSX-5 spacecraft. An intense solar proton event commenced on 28 October 2003, and was followed by a very large geomagnetic storm with two distinct Dst minima recorded on 30 October at 01 hr UT (-363 nT) and 23 hr UT (-401 nT). An intense injection of electrons into the slot region followed, with $>$1.2 MeV fluxes peaking at L=2.5 on 02 November and subsequently decaying away over the next several weeks. The July 2004 storm interval was marked by a Dst index that exhibited three distinct minima of -104 nT (23 July), -150 nT (25 July), and -182 nT (27 July). This active period produced an enhanced MeV electron population that peaked between L=3-4 and penetrated to L=2. The fluxes remained above pre-storm levels for several weeks. Although the 2004 storm period did not produce as large a negative Dst excursion as the 2003 storm, it produced more intense fluxes and a much harder spectrum. The MeV electron spectra and decay profiles throughout the two storm periods will be compared and discussed.
SM41A-1129 0800h
Electron Flux Prediction in the Radiation Belt via Autoregressive Models With Solar Wind Drivers
Several prior studies have suggested the solar wind velocity acts as a driver for the relativistic electron flux in the radiation belts. In this study, time series of ACE solar wind velocity measurements are included along with past electron flux measurements from SAMPEX in order to predict future electron flux. Since previous flux measurements are used to predict future flux, the autoregressive model is chosen. The inclusion of solar wind velocity measurements can also be modeled by an autoregressive equation. Since the entire model remains autoregressive, the Kalman filter state and measurement vectors are augmented to accommodate previous solar wind velocity along with the previous electron flux measurements. The filter processes these measurements as they become available at different rates. ACE measurements are updated more frequently than SAMPEX. The filter identifies the model coefficients of electron flux and solar wind velocity recursively, so that the coefficient estimates are optimal up to the time of the most recent measurement. The improvement in prediction accuracy over coefficient identification using Kalman filters without solar wind velocity is assessed. As a self consistent check, the autocorrelation function for the solar wind velocity with time, using actual ACE solar wind measurement data is computed justifying the modeling of solar wind velocity by an autoregressive equation.
SM41A-1130 0800h
Predicting Radiation Belt Electron Flux with Adaptive Linear State-Space Models
Linear state-space models, most common in engineering applications, offer a more flexible alternative to the familiar finite impulse response (FIR) linear prediction filters commonly used to predict radiation belt electron fluxes based on solar wind input. They can be designed to be mathematically equivalent to FIR models, but may also incorporate dynamic feedback and allow cross-coupling between multiple system outputs, thereby providing an empirically derived description of a system's dynamics that is more consistent with reality. In addition, their numerical structure is ideally suited for use with the Kalman Filter as a form of data assimilation, and/or the so-called extended Kalman Filter for adaptive identification of optimal model parameters. A brief overview of linear state-space models is given, followed by a demonstration of their ability to predict 2-6 MeV electron fluxes based on historical solar wind data and SAMPEX electron observations binned by geomagnetic L-shell (1-8 RE).
SM41A-1131 0800h
Magnetic field line curvature induced pitch angle diffusion in the radiation belts
Magnetic field line curvature (FLC) affects particle populations throughout the magnetosphere. Strongly curved field lines quickly isotropize particle distributions with relatively low energies in the tail and keep the loss cone well supplied. In the inner magnetosphere, weaker curvature allows higher energy particles to remain trapped for longer periods of time, but limits on lifetimes are still imposed. Because of the exponential nature of the onset of non-adiabaticity (leading to pitch angle scattering), rough estimates for the importance of this mechanism assume an ``on/off'' switch. If $\varepsilon$ is above threshold, the particles are quickly scattered, while populations with $\varepsilon$ below this value are not affected at all. Here $\varepsilon$ is the ratio between the maximum gyroradius a particle on a particular field line may have and that field line's minimum radius of curvature. We investigate the effects of magnetic field line curvature in the inner magnetosphere using the pitch angle diffusion equation for phase space density with the diffusion coefficient based on an empirically derived FLC induced pitch angle scattering model. A range of numerically calculated results shows the effects of varying not only $\varepsilon$, but various magnetic field parameters. Using these results in conjunction with magnetic field parameters calculated from a combination of the Tsygenenko 2001 and IGRF magnetic field models we explore the effects of both $D_{st}$ and the dipole tilt angle on different particle populations. We show results that support the ``on/off'' model with threshold values of $\varepsilon$ varying between 0.15 and 0.38. Higher speed populations do not require as large of values of $\varepsilon$ to diffuse at the same rate as lower speed populations.
SM41A-1132 0800h
Statistical Pitch Angle Properties of Substorm Injected Electron Clouds and Their Relation to Dawnside Energetic Electron Precipitation
Using the existing large database of geosynchronous orbit particle measurements from Los Alamos instruments, statistical properties of substorm injected electron clouds are investigated, with special focus on the pitch angle distribution (PAD). The equatorial plasma sheet at 6.6R$_E$ does in general show some anisotropy and its PADs are probably caused by the combined influence of drift orbits, different for each energy and pitch angle, and pitch angle diffusion due to waves. The statistical results of this paper indicate that the PADs during intervals of increased electron flux at energies greater than 10keV from midnight till noon are dominated by pitch angle diffusion by interaction with waves. The strength of the pitch angle diffusion is seen to initially limit the growth of anisotropy from differential drift speeds and orbits and later on to increase the anisotropy. After local noon we find evidence that pitch angle diffusion is no longer important and the PADs are evolving due to differential drift effects.