SM21A-1651
RCM-VERB Coupled Simulations of the Dynamics of the Radiation Belts During Storms
The evolution of the relativistic electron fluxes in the radiation belts can be described by the 3D modified Fokker-Planck equation in terms of radial distance, pitch-angle, and energy. Recently developed at UCLA, the VERB code models the dynamics of relativistic electrons subjected to ULF, ELF, and VLF waves including radial diffusion driven by PC4-5 waves; pitch-angle scattering by hiss, chorus, anthropogenic whistlers, lightning generated whistlers, and EMIC waves; and local acceleration driven by chorus waves. Numerical simulations are presented of a geomagnetic storm using the VERB code, coupled with RCM. Dynamics of the 10-100 keV electrons at L*=7 is inferred from RCM simulations and is used as a boundary condition for the VERB code for the radial diffusion operator. Numerical simulations are also presented of the sensitivity of radiation belt electron response to the seed population of electrons.
SM21A-1652
The Role of EMIC Waves in the Outer Radiation Belt Losses
Complex response of electron fluxes to varying geomagnetic activity is determined by multiple competing electron acceleration and loss mechanisms. Mechanisms act on both 'global' scales, braking the second and/or the third invariant of trapped electrons, and on 'local' scales, breaking the first invariant. Predictive understanding of the outer belt can be achieved only by quantifying contributions of individual local and global mechanisms to global variability of relativistic electron fluxes. One of the local loss mechanisms of radiation belt electron is pith-angle scattering by Electromagnetic Ion Cyclotron (EMIC) waves. In this work we use data from multiple spacecraft to investigate EMIC wave properties which determine their efficiency in scattering radiation belt electrons.
SM21A-1653
Reanalysis of Radiation Belt Electron Phase Space Density Using CRRES and Akebono Observations
Knowledge of the radial profile of the electron phase space density (PSD) is essential for understanding and quantifying the dynamical evolution of the radiation belts. However, such radial PSD information is difficult to obtain since space-borne observations are limited to a single point in space and may depend on the accuracy of the instrument and the accuracy of the magnetic field model. As a potential solution to the above problem, data assimilation technique provides algorithms which can allow us blend incomplete and inaccurate data with physics based dynamical model. To estimate the accuracy and to verify the results of data assimilation, in this study we perform reanalysis of the radial profile of PSD using two independent data sources from the nearly equatorial CRRES MEA observations and the polar-orbiting Akebono measurements for a 50-day period starting on 18 August 1990. In this study we use the UCLA 1D VERB code and a Kalman filtering approach. Comparison of the reanalyses shows that robust peaks in PSD are present in both of the reanalyses, and that the dynamics of the PSD obtained with data assimilation using CRRES and Akebono compare favorably to each other. In particular reanalyses show favorable agreements in the locations and magnitudes of PSD peaks and the magnitudes and radial extent of the decays. Our study not only further confirms the advantage of data assimilation technique in capturing a complete and reasonable picture of the radiation belts but also suggests an important tool for inter-calibration of satellites.
SM21A-1654
Simulations of Pitch-angle Scattering of Relativistic Electrons With MLT-Dependent Diffusion Coefficients
We present MLT-dependent simulations of pitch-angle scattering of relativistic (~MeV) electrons by chorus and EMIC waves. Numerical simulations indicate that in the case of scattering by chorus waves, pitch-angle distribution is relatively independent of MLT. In the case of scattering by EMIC and chorus waves, the modeled pitch-angle distribution shows significant variations with MLT. MLT-averaged simulations tend to overestimate net loss during a storm, but can accurately predict equilibrium loss rates and the overall shape of the pitch-angle distribution. Numerical simulations show that EMIC waves not only scatter electrons into the loss cone, but also create gradients in the pitch-angle distribution, assisting chorus waves in scattering of relativistic electrons into the loss cone. We also show that changes in the spectral properties of waves can significantly change loss rates. Loss rates reach a maximum level for EMIC waves with amplitudes above approximately 1 nT, present over a few percent of the drift orbit and then become relatively independent of the amplitudes of EMIC waves.
SM21A-1655
Scaling of Energetic Geosynchronous Electrons to a Constant Mu -- Examples and Technique Validity
Geosynchronous energetic electrons are highly varying due to many overlapping influences. The observed change in particle flux includes an adiabatic response to changes in field geometry. By scaling measured flux to phase space density at a constant value of the first adiabatic invariant, mu, we remove much of this response. This will allow a clearer analysis of the other influences on the particle populations themselves, such as wave-particle interactions and radial diffusion. From a dataset of nearly a solar cycle of GOES data scaled to a constant mu of 1000 MeV/G and 5000 MeV/G, we highlight several examples when the flux time- series scaled to a constant mu differs from the constant energy time-series, as directly measured by the detector. We also present an analysis of the effectiveness of a technique for specification of geosynchronous electrons using this constant mu approach and evaluate the additional contributions of the adiabatic invariants L* and K to flux variability.
SM21A-1656
Electromagnetic Ion Cyclotron Fluctuations and Fast Electron Scattering: Hybrid Simulations
Two dimensional electromagnetic hybrid simulations in a magnetized, homogeneous, collisionless plasma with a single ion species yield enhanced electromagnetic ion cyclotron (EMIC) fluctuations due to the growth of the ion cyclotron instability driven by T⊥ i > T∥ i. The research described here addresses fundamental properties of such enhanced fluctuations, in preparation for future studies on their interaction with fast electrons, with the ultimate goal of understanding how EMIC wave-particle scattering leads to trapping and untrapping of relativistic electrons in the terrestrial magnetosphere. Self-consistent magnetic fluctuation spectra from the hybrid simulations will be used to examine the approximations often used in quasilinear theories of fast electron scattering by EMIC fluctuations. These approximations include the assumptions (1) that the fluctuation power spectrum has a Gaussian distribution in frequency, (2) that fluctuation dispersion is given by linear cold plasma theory, and (3) that the fluctuations propagate only parallel or antiparallel to the background magnetic field. We also will describe preliminary test particle computations intended to address the further quasilinear assumption (4) that the fluctuating fields are small enough in amplitude that the wave-particle interactions can be described by a Fokker-Planck-type diffusion equation.
SM21A-1657
Generation of Polarized Shear Alfvén Waves by a Rotating Magnetic Field Source
It is widely known that shear Alfvén waves play an important role in auroral physics and it has been suggested that they might even power the aurora. Recent experiments conducted in the Large Plasma Device (LAPD) have added to our basic understanding of these high amplitude waves. We report on the generation and characterization of field aligned, polarized, kinetic shear Alfvén waves radiated from a rotating magnetic field source created via a novel phased orthogonal loop antenna. Both right and left hand polarization's are generated at a wide range of frequencies from 0.01≤ω/Ωci≤1.0. Propagation parallel to the background magnetic field at the Alfvén velocity is observed along with a negligible parallel wave magnetic field component implying a shear mode. The magnitude of the waves magnetic field is on the order of 0.4% of the background field. Small amplitude second harmonic generation is seen along with indirect evidence of electron heating and/or fast electrons during the pulse implying non- linear response. The work was supported by ONR MURI Grant N000140710789.
SM21A-1658
Occurrence Patterns of Magnetospheric EMIC Waves During Geomagnetic Storms: Ground-based Observations at Auroral and Subauroral Latitudes
Electromagnetic ion cyclotron (EMIC) waves in Earth's magnetosphere have been suggested in many theoretical and observational studies as a significant loss mechanism for both ring current ions and, via parasitic interactions, radiation belt electrons. Several early ground-based studies noted their occurrence was reduced during the main phase of geomagnetic storms and increased during recovery phase, but few comprehensive studies of the long-term occurrence of these waves have been presented. We have applied the automated wave analysis technique developed by Bortnik et al. [JGR A04204, 2007] to a set of data recorded from 1996 through 2005 by search coil magnetometers deployed at auroral and sub-auroral latitudes in Antarctica. Superposed epoch analysis of these data sets during magnetic storms and high speed stream intervals shows that at auroral latitudes (L = 6 - 8) the highest occurrence probability was near or slightly before storm onset, near or slightly after local noon, with a relative minimum soon after. The peak at onset seems quite consistent with what has been observed in earlier studies of waves stimulated by sudden impulses and magnetospheric compressions, causing Pc 1 events in the outer dayside magnetosphere. At somewhat lower latitude (Halley, L = 4.56), the local time of the occurrence peak at onset was shifted a few hours later, toward early afternoon, and there was again a relative minimum during main phase and early recovery phase. At both auroral and sub-auroral latitudes the occurrence frequency became larger and somewhat more isotropic in local time during later recovery phase, but remained high near noon. These results contrast with the recent observations at L = 1.77 of Bortnik et al. [JGR A04201, 2008], who found a strong diurnal occurrence maximum during nighttime hours during all storm phases. Longer-term variations include a relative minimum at auroral latitudes during solar maximum conditions, again consistent with earlier observations.
SM21A-1659
Quantitative Estimations of Relativistic Electron Drift Loss Effect during Geomagnetic Storms
It has been suggested that drift loss to the magnetopause can be one of the major loss mechanisms
contributing to relativistic electron flux dropouts. The flux of relativistic electrons that usually decreases
during the storm main phase sometimes never recovers to their pre-storm time level at the end of a storm.
This suggests the possibility that electrons at high L-shells can move outward aided by the Dst effect and
then be drift-lost by encountering the magnetopause, leading to flux dropouts at inner L-shells. In this study,
we determine the extent to which the drift loss through the magnetopause as combined with the Dst effect is
important to the total loss of the outer radiation belt. We test this effect quantitatively for three groups of
magnetic storms as obtained by classifying 95 storms according to their Dst minimum intensities and have
performed the calculation of drift paths of relativistic electrons' guiding center under the Tsyganenko T02
model. It is shown that generally a prestorm electron that drifts in an inner region with a particular energy and
pitch angle moves outward by the Dst effect and appear at an outer region with a lower energy and pitch
angle during the storm main phase. The effect that electrons that do not return back to where it was initially
due to the drift loss effect after the full recovery of the storm is seen at regions of r down to 5RE for
storms of moderate intensity (-100nT
SM21A-1660
Statistical Analysis of the Global Distribution of Electrons for the Chorus Generation Observed on the THEMIS Spacecraft
The intensification of the whistler-mode chorus emissions is observed in the low-density region outside the plasmapause during the injection of anisotropic plasmasheet electrons into the inner magnetosphere. A statistical analysis is performed to provide the global distribution of chorus waves and electrons in the energy range of 0.1-100keV near the equatorial plane using the data measured with ESA from the THEMIS spacecraft. The electron flux and corresponding electron anisotropy are categorized via different levels of the chorus intensity at different MLT and L-shells. Electron distribution data are also sorted by various energy ranges of 0.1-1keV, 1-30keV, and 30-100keV in order to identify the energy of electrons, which play a most important role in chorus generation. The results show that chorus waves are generated by the injection of electrons with the energy of a few keV and tens of keV and stronger chorus waves are associated with higher electron flux and larger electron anisotropy. In addition, compared to the nightside, electron flux is lower and the anisotropy is higher on the dayside.
SM21A-1661
Low-latitude Pi2 Pulsations observed by an FM-CW Radar and CPMN Stations
At the onset of magnetospheric substorms, impulsive hydromagnetic oscillations occur globally in the magnetosphere with a period range from 40 to 150 seconds [e.g. Saito, 1968]. They are called Pi 2 magnetic pulsations. Pi 2 has been studied with arrays of magnetometers on the ground and with in-situ observation by satellites [e.g. Yumoto, 2001]. However characteristics of Pi 2 electric pulsations in the low-latitude ionosphere have not been clearly identified yet. We have focused on measuring the Pi 2 electric pulsations by an FM-CW (Frequency Modulated Continuous Wave) radar and clarify their characteristics. In order to detect the ionospheric electric fields, we built a FM-CW (HF) radar at Sasaguri (Magnetic Latitude: 23.2 degree, Magnetic Longitude: 199.6 degree), Fukuoka, Japan in 2002. The radar provides the Doppler shift of launched wave frequencies, which corresponds to the height variation of the ionosphere, with a high- time resolution of 3 sec. When the eastward (westward) electric field penetrates into the low-latitude ionosphere, it drifts upward (downward) through the ExB drift. Thus, using the FM-CW radar we can measure east-west electric fields (Ey) in the ionosphere [see Ikeda et al., 2008]. In this study, we also used geomagnetic field data BH at Kujyu (KUJ; M. Lat. 23.6 degree, M. Lon. 203.2 degree), a part of Circum-pan Pacific Magnetic Network (CPMN) stations [cf., Yumoto et al., 2001]. The first Pi 2 event was observed at KUJ and Sasaguri simultaneously at 1332 UT (2232 LT) on 6 November, 2003. Also positive bay was detected in the H-component (BH) at KUJ. The dominant frequencies of the electric field Ey and magnetic field BH were identical. From a cross-correlation analysis between the BH at KUJ and Ey at Sasaguri, we found that the correlation coefficient is 0.80 and phase delay is about -100 degree. Takahashi et al. (JGR, 2001) showed the expected phase relation between magnetic field of cavity- mode Pi 2 and associated electric field. Based on their result, we suggest the phase delay of -100 degree indicates that the first Pi 2 event shows a radial mode structure of cavity-mode Pi 2. The second Pi 2 event was observed at 1415 UT (2315 LT) on the same day 6 November, 2003. The dominant frequency of Ey and BH were the same and phase delay is -148 or 39 degree. Since the phase delay is almost -180 or 0 degree, this Pi 2 event can be described by as a propagating mode. Further we analyzed 26 Pi 2 events that were recorded by a CPMN magnetometer at KUJ or Kagoshima (KAG; Magnetic Latitude: 21.9 degree, Magnetic Longitude: 203.2 degree) and the FM-CW radar simultaneously within a period from Nov. 2003 to Apr. 2004. The criteria of the analyzed Pi 2 events are that Pi 2 magnetic amplitude range of the BH is more than 1 nT at KUJ or KAG. In 12 of all 26 Pi 2 events, the dominant frequency of Ey and BH are identical. Moreover we examined the phase delay of 12 Pi 2 events, and found that the only 3 events in midnight sector show the radial mode structure of cavity-mode Pi 2. Other 9 events show a propagating mode of Pi 2. The observed low-latitude Pi 2s are concluded not to be described as a simple standing or propagating mode.
SM21A-1662
Investigation of Relativistic Electron Resonance with EMIC Waves
Wave-particle interaction of relativistic electrons with EMIC waves has been proposed as an important loss mechanism for radiation belt electrons (e.g. Thorne and Andreoli, 1980). Lorentzen et al (2000) and Millan et al (2002) suggested this mechanism to be responsible for dusk side relativistic electron precipitation (REP) detected by balloon borne instrumentation. This study will use the linear electromagnetic dispersion code WHAMP to investigate the effects of density, magnetic field, anisotropy, and heavy ions on the minimum resonance energy for relativistic electrons with EMIC waves. Results will be compared with observations of REP during the MAXIS balloon campaign on Jan. 19, 2000 and the MINIS balloon campaign on Jan. 21, 2005.
SM21A-1663
Generation of Whistler Wave by a Rotating Magnetic Field Source
The interaction of Rotating Magnetic Fields (RMF) with plasmas is a fundamental plasma physics problem with implications to fusion related Field-Reversed Configurations (FRC), space propulsion, astronaut protection from cosmic rays in long interstellar travel, control of the energetic population in the radiation belts and near zone processes in pulsar magnetospheres. In this paper we report recent experiments on the generation of whistler waves with a new type RMF-based antenna. The experiments were conducted on UCLA's Large Plasma Device (LAPD). The Rotating Magnetic Field (RMF) is created using poly-phased loop antennas. A number of parameter combinations, e.g. plasma density, background magnetic field, and driving current, were used. It was found that RMF created by a two phase-delayed loop antenna drives significant currents along the ambient magnetic field. The measured amplitude of induced wave field was proportional to the square-root of the plasma density. The spatial decay rate for the wave perturbation across the background magnetic field was found to scale with the plasma skin depth. A small amplitude second harmonic was also measured. The paper will also present analytic and simulation results that account for the experimental results; in particular, the scaling of the induced magnetic field as a function of the RMF and plasma parameters and the spatial decay rate of magnetic field. Applications of RMF as an efficient radiation source of plasma waves in space plasmas will be discussed. This work was sponsored by ONR MURI Grant 5-28828
SM21A-1664
Modeling Alfven and Whistler Waves Generation by Rotating Magnetic Field Source
Recent experiments by Gigliotti et all., 2008 and Karavaev et al., 2008 (two posters in this meeting) demonstrated excitation of shear Alfven wave and whistler wave, respectively, by Rotating Magnetic Fields (RMF) created by a phased orthogonal loop antenna. This paper presents a combination of computational results along with experiments that emphasize the RMF properties for generating MHD and whistler waves. For RMF rotating frequencies in the whistler wave frequency range, the electrons quickly come to a co- rotation with the RMF, generating a differential azimuthal current. For rotating frequencies below the ion cyclotron frequency wave, the electrons and ion motion decouple within the ion skin-depth near the antenna and co-rotates with the RMF outside the ion skin depth, generating a JxB force. In order to understand the RMF and plasma interaction and the resultant radiation in different frequency regimes, we developed a 3D code that simulate the process. The code solves the linearized Maxwell equations coupled to the two-fluid description of the plasma motion in the frequency-domain. The antenna excitation is modeled as a set ofexternal current sources. The magnetized plasma response to the wave excitation at different frequencies,i.e. in the MHD and whistler frequency regime, are described by elements of the dielectric tensor. An iterative sparse matrix-solver is used to solve for the near field antenna-plasma coupling and the far-field wave propagation. The code is able to determine the radiation from antennas with complex geometry. The experimental configurations used in Gigliotti et all., 2008 and Karavaev et al., 2008 were simulated. The simulation results help us understand the general characteristics of impedance matching, energy coupling and far field radiation pattern from an RMF antenna in plasmas. The scaling of the induced magnetic field as a function of the RMF frequency, the plasma parameters and the spatial decay rate of magnetic field, as well as the use of RMFs as efficient radiation sources of MHD and whistler waves in space plasmas are also discussed. This work was sponsored by ONR MURI Grant 5-28828
SM21A-1665
Formation of Double Layer-Like Structures in Ionospheric Alfven Resonator
A two-dimensional numerical multi-fluid MHD model describing excitation of ionospheric Alfvén resonator (IAR) by a shear Alfvén wave is developed. In the model, the plasma consists of hydrogen and oxygen ions and electrons with finite temperatures. The nonlinear Lorentz force of the Alfvén wave, gravity force, and thermal pressure are included. The simulated area extends from the top-side ionosphere up to altitudes of a few Earth radii. The model uses density and temperature profiles typical for high-latitude auroral regions. For cold plasmas, Sydorenko, Rankin, and Kabin (2008) have found that the nonlinear force of standing IAR oscillations can produce deep density cavities in less than one minute that are similar to the ones observed in low-altitude magnetosphere. Here it is shown that at later stages (more than about one minute after the beginning of simulation), thermal pressure effects play an important role: perturbation of the initial equilibrium state by electron and ion flows that are created by the nonlinear Lorentz force amplifies the electric field directed along the geomagnetic field in proportion to the density gradient. Light hydrogen ions are accelerated by this electric field much stronger than the heavy oxygen ions. Eventually, at some locations the hydrogen ion flow speed may approach and even exceed the local sound speed. In this case, simulation reveals double layer-like structures with strong (about 0.1 mV/m) localized electric field directed upward. Evolution of such structures depends on the density and temperature profiles, as well as on the amplitude and frequency of the excited IAR eigenmode. The present study qualitatively supports available satellite measurements of intense parallel electrostatic fields in plasma cavities in the low-altitude magnetosphere [e.g., Chaston et al., 2007]. Chaston, C. C. et al., (2007), J. Geophys. Res., 112, A05215, doi:10.1029/2006JA012007. Sydorenko D., R. Rankin, and K. Kabin (2008), J. Geophys. Res., doi:10.1029/2008JA013579, in press.
SM21A-1666
A loss mechanism of relativistic electrons in the outer radiation belt during quiet times: Test-particle simulation
Some observations have shown high energy electron flux decreases after an enhancement of solar wind dynamic pressure. The events have been observed even in non-magnetic storm time. In this study, a loss mechanism of relativistic electrons in the outer radiation belt during non-magnetic storm time is studied by test-particle simulation using the 2D guiding center equations on the equatorial plane. The empirical magnetic field, which is calculated from the Tsyganenko model TS05, is applied to the simulations by using the solar wind data obtained from a spacecraft. In the simulations, the inductive electric field caused by solar wind dynamic pressure variation is applied, following Ukhorskiy et al. (2006). We compare the simulated flux variation with the GOES observed MeV electrons, and discuss the effect of the solar wind dynamic pressure variation on the loss of relativistic electrons at geostationary orbit.
SM21A-1667
Database of measurements of magnetosonic equatorial noise emissions from measurements of the CLUSTER spacecraft
Equatorial noise is an intense wave emission generated
by unstable ion distributions. It occurs in the inner magnetosphere
at frequencies below the local lower hybrid frequency.
Recent studies have shown that these waves could be able to
contribute to the local acceleration of energetic electrons in the outer
Van Allen belts.
We present a unique database of many observations of equatorial noise
selected from wave measurements obtained by the four CLUSTER spacecraft.
All these events have been visually selected from the onboard-analyzed
time-frequency spectrograms and from the wave
polarization data recorded by the STAFF-SA instruments,
and from high-resolution spectrograms obtained from the
measurements of the WBD instruments. Our database includes
all available measurements between 2001 and 2007.
We construct a list of events, which are selected according
to several criteria. We choose data measured within 5 degrees
of the geomagnetic equator, where emissions below the lower hybrid frequency
are clearly visible in both the magnetic and electric field spectrograms, with
power-spectral densities of at least
10-6 nT2Hz-1 and 10-5 mV2m-2Hz-1, respectively.
We also select only those events which have nearly linearly polarized
magnetic field fluctuations, with ellipticities
from -0.2 to 0.2, consistent with published past
observations. Obtained results show that equatorial noise is present at
all magnetic local times. We show examples of fine spectral structures
in the observed equatorial noise emissions.
http://os.matfyz.cz/papers/agu2008/
SM21A-1668
Relativistic Microbursts and their Relationship to Observed Plasmapause Location
Relativistic microbursts are short (<1 sec) duration bursts of precipitating relativistic electrons observed in low Earth orbit. Microburst activity is often higher for days following geomagnetic storms and is believed to result from interactions between trapped radiation belt electrons and intense whistler chorus waves. This is thought to be an important process for stormtime depletion of the outer radiation belt and/or an indicator of whistler energization and repopulation of outer belt electrons. These wave-particle interactions are optimized outside the plasmapause, leading to a dependence of microburst locations on plasmapause location. We present results on the location of SAMPEX-observed microbursts with respect to changes in the location of the plasmapause as observed by the DMSP satellites. Innermost microburst locations are well correlated with outermost plasmapause locations, with microbursts located outside the plasmapause. We also discuss the timescale of variations in microburst and plasmapause location.
SM21A-1669
Hybrid Simulation of EMIC Waves in Curvilinear Coordinates
Electromagnetic Ion Cyclotron (EMIC) waves play an important role in the Earth's Radiation Belts dynamics. Theoretical work has suggested EMIC waves may contribute significantly to Relativistic Electron Precipitation (REP) by pitch-angle scattering. We will be self-consistently simulating the EMIC instability, wave propagation, and wave-particle interaction using a hybrid code, in which ions are treated as super particles and electrons as a massless fluid. While most of the numerical simulations on EMIC waves have been done in Cartesian coordinates, we will carry on our simulation in generalized orthogonal curvilinear coordinates. The generalized coordinates fit better especially for geometries that have irregular boundary shapes, which is often the case in the Earth's radiation belts. An energy-conserving particle mover in curvilinear coordinates will be presented, as well as reflection boundary conditions for particles. We will also discuss the power spectrum method in Fourier space used to analyze the waves. Simulation results in different coordinates (e.g. Cartesian and dipole) of different dimensions (1D and 2D) will be presented to compare with linear theory.
SM21A-1670
Gyrokinetic Particle Simulation Of Drift Compressional Mode In Magnetic Dipole Geometry
The Pc5 magnetic pulsations dominated by compressional modes have been regularly observed in the Earth's magnetosphere. The objective of this project is to study the linear excitation and nonlinear evolution of these ultra low frequency pulsations, focusing on unstable magnetic trapped particle modes, with kinetic effects due to wave-particle resonance and finite Larmor radius. The method is to develop a three dimensional gyrokinetic particle simulation, with the dipole equilibrium field modeling the Earth's magnetosphere. Currently the code is being benchmarked against analytic results in a simple limit.
SM21A-1671
Pc 1-2 wave ducting within the ionospheric wave guide
Pc 1-2 waves are commonly observed on the ground at high latitudes. An important subset of these waves are electromagnetic ion cyclotron (EMIC) waves, which are believed to play an important role in radiation belt dynamics. Theories of wave propagation in the ionosphere predict that waves at these frequencies will be ducted within the ionospheric wave guide and experimental data exists that are approximately consistent with these theories. In this study, we present results from a statistical study on ducting as observed in the Antarctic, using an extended array of observatories. With coverage of geomagnetic latitudes from 62 to 87 degrees and good alignment along the magnetic meridian, search-coil magnetometers operating at manned stations and on the Automated Geophysical Observatories (AGOs) show clear ducting of these waves. Data from 2007 reveal more than 150 events from Halley Bay, P1, P2, P3, P5, and South Pole stations that provide an excellent opportunity for quantifying ducting phenomena under various conditions, such as daylit versus dark ionospheres, storm times, etc. Results from the study show wave power attenuation, propagation speeds, and polarization for each event.
SM21A-1672
Polar spacecraft measured evolution of large scale and Alfvenic Poynting flux during major geomagnetic storms in the inner magnetosphere
In this poster we present the first study of the time evolution of the field aligned Poynting flux as determined from spacecraft observation over the onset, main phase and recovery phase of major geomagnetic storms as determined by the DST index. This study uses electric and magnetic field data from the Polar spacecraft taken from April 27 though May 9, 1998 and October 17 through October 27, 2001 while Polar was on the night side of the Earth positioned at a radial distance of 2.5 to 6 Earth radii This study is concerned with two kinds of Poynting flux. The first is Alfvenic Poynting flux ( <3 minutes duration) . The second kind is large scale Poynting flux associated with the convection electric and field aligned current system ( 3 - 40 min.). The peak intensity for large scale Poynting flux shows a moderate increase during active conditions: from ~0.1 mW/m2 during quiet times to ~0.15 mW/m2 during active times. The intensity for Alfvenic Poynting flux shows 1-2 orders of magnitude increase from the lowest values observed during quiet times to the largest values observed during the main phase and recovery phases of the storm. There is significant Alfvenic pointing flux observed preceeding the storm possibly in association with substorm activity. The maximum value of the Alfvenic Poynting flux observed during the storm periods was -0. 1- 0.5 mW/m2. If mapped along converging magnetic field lines to 100 km altitude, these peak Poynting flux values correspond to 10- 50 mW/m2. This value is about a factor of two larger than the typical energy fluxes associated with broad band magnetic field-aligned electrons observed by low altitude spacecraft at low latitudes. This work provides evidence that both Alfvenic and large scale Poynting flux are significant energy inputs into low altitudes at low latitudes. It also provides evidence that Poynting flux in the inner magnetosphere can provide enough energy to power the low altitude acceleration of broad band electrons. We will present particle data from the FAST spacecraft in order to provide measurements of electron energy flux during these storm periods.
SM21A-1673
Examining EMIC Waves Observed at Geosynchronous Orbit During Storms, Directly and as Inferred From the Plasma Population
There is still much to be understood about the processes contributing to relativistic electron enhancements and losses in the radiation belts. Wave particle interactions with both whistler and electromagnetic ion cyclotron (EMIC) waves may precipitate or accelerate these electrons. In this study we examine the link between EMIC waves and resulting relativistic electron flux levels after geomagnetic storms. Using LANL MPA plasma data from geosynchronous orbit, in conjunction with linear theory, we develop a proxy for EMIC wave growth. In a statistical study using superposed epoch analysis, we find that for storms resulting in net relativistic electron losses, there is a greater occurrence of EMIC mode waves at higher growth rates. This is consistent with the belief that EMIC waves are a primary mechanism for scattering of relativistic electrons, and thus cause losses of such particles. We use the proxy to examine the likely presence of these waves as functions of both local time and storm epoch time and compare our inferred wave characteristics to in situ wave measurements from high-resolution GOES magnetometer data. Through this comparison, we can quantify the correlation between our EMIC wave growth proxy and direct wave measurements, both measured at geosynchronous orbit. This result enables broader understanding of the powerful applications of using plasma data to infer wave distributions in space.
SM21A-1674
Waves in the Inner Radiation Belt and Electron Slot Region Observed on the STEREO spacecraft
We present a survey and analysis of waveforms captured on the Time Domain Sampler (TDS) instruments of the two STEREO spacecraft during four perigee passes through the Earth's plasmasphere and magnetosphere in 2006. Of particular focus in this analysis are waves in the inner radiation belt and slot region such as large amplitude whistler mode waves. Because of instrumental limitations on other spacecraft whistler mode emissions identified in past studies have typically been seen with maximum amplitudes of 30 mV/m. The TDS instrument on STEREO however is capable of capturing much larger amplitude waveforms. The whistler mode emissions observed in this survey range in amplitude from 50 mV/m up to 200 mV/m. Some of these waves are seen to propagate with large wave normal angles with respect to the DC magnetic field and occur along with an enhanced flux of MeV electrons. Preliminary studies of similar amplitude whistler mode emissions in the outer belt have indicated that large pitch angle scattering and energization of electrons by MeVs can occur due to the waves.
SM21A-1675
Generation of Lower Hybrid Turbulence in the Ionosphere and its Evolution in the Magnetosphere
A previous work considered the generation of ULF waves in the inner Magnetosphere due to a heavy ion ring distribution such as Lithium [Ganguli et al., 2007]. We extend this analysis by considering the generation of Lower-hybrid waves in an Oxygen dominated plasma at R~550km due to a Barium ion ring distribution. We demonstrate the criteria in which Lower-hybrid waves are produced and examine the quasilinear evolution of the instability. The quasilinear evolution of the Barium ring distribution lowers the instability threshold. The analysis is compared with space experiments done several decades ago. We conclude that the strong turbulence generated by such a release can increase wave activity in the plasmasphere. Ganguli, G., L. Rudakov, M. Mithaiwala, and K. Papadopoulos (2007), Generation and evolution of intense ion cyclotron turbulence by artificial plasma cloud in the magnetosphere, J. Geophys. Res., 112, A06231, doi:10.1029/2006JA012162.
SM21A-1676
Landau Damping and Growth of Proton-Cyclotron Turbulence by the Electron Distribution Function in Downward Auroral-Current Regions
We have identified several FAST satellite passes in downward, field-aligned, auroral-current regions, where Landau damping and Landau growth of proton-cyclotron turbulence is correlated with the shape of the electron distribution function in velocity space. Recently, and for the first time, we have developed and published a new kinetic and multi-moment fluid, anomalous transport theory that contains the effect of electrostatic turbulence in inhomogeneous, non-uniformly magnetized plasmas [1, 2]. We apply the new theory to a downward current sheet and show that a current-driven, generalized, Drummond-Rosenbluth, electrostatic proton-cyclotron instability occurs, where the time-asymptotic state for the spectral density of the turbulent electric field fluctuates between maximum and minimum values; and that these maximum and minimum values are, in turn, correlated with fluctuations in the electron distribution function between unstable and stable configurations, respectively. In this way, the time-asymptotic state for downward, auroral-current regions is characterized by "hot spots" and "cold spots" which are intermittent in space and time. [1] J. R. Jasperse et al.(2006), Phys. Plasmas 13, 072903, and [2] J. R. Jasperse et al. (2006), Phys. Plasmas 13, 112902.
SM21A-1677
What Supports the Parallel Electric Field in the Birkeland (Field-Aligned) Current Regions of the Earth's Magnetosphere?
Quasi-steady electric fields parallel to the background geomagnetic field exist in both upward and downward Birkeland (field-aligned) current regions above the aurora. These fields, together with the turbulence found on auroral field lines, energize the plasma particles as they flow either away from or toward the earth. In general, these parallel electric fields are supported by one or more strong double layers, the mirror force, the generalized pressure gradient, and the anomalous resistivity due to the turbulence. Recently, and for the first time, we have developed and published a new kinetic and multi-moment fluid, anomalous transport theory that contains the effect of electrostatic turbulence for inhomogeneous, non-uniformly magnetized plasmas [1, 2]. Applying the new theory to observations in a downward-current sheet, we show that anomalous resistivity accounts for only a small portion of the parallel electric field and that contributions from the double layer, mirror force, and generalized pressure gradient terms in the generalized Ohm's law for the problem are more important. Calculations in the double-layer-and-transition-propagation region for a downward-current sheet show that a strong double layer forms, propagates upward at the local ion-acoustic speed, is destabilized as the current falls below the local critical value, and reforms at a lower altitude. These results have important implications in other regions of space such as magnetospheric reconnection sites and solar coronal loops where parallel electric fields are likely to exist. [1] J. R. Jasperse et al. (2006), Phys. Plasmas 13, 072903, and [2] J. R. Jasperse et al. (2006), Phys. Plasmas 13, 112902.
SM21A-1678
Storm-Dependent Radiation Belt Electron Dynamics
Using recently published electron phase space densities (PSD) as a function of L (L is approximately the radial distance in Earth radii at the equator) and time, energization and loss in the Earth's outer electron radiation belt were studied quantitatively and numerically using a radial diffusion model that included finite electron lifetimes and an internal source parameterized as a function of geomagnetic indices. PSD data at fixed first and second adiabatic invariants, corresponding to fairly energetic electrons at L=4 (2.7 MeV) mirroring near the Earth's equator were used. Model results for the second half of 2002 reproduced the average variations of the radiation belt electron PSD between L=2.5 and L=6 but with over-prediction and under-prediction at different times, implying that the same set of parameters cannot be applied to all storms. A detailed analysis of four individual storms showed that while electrons in three storms could be well simulated by energization from either radial diffusion only or internal heating only, incorporating both yielded the best results. For the other storm, an additional source of electrons was required to account for the enhanced PSD. The model results indicated that each storm is best simulated when combination of radial diffusion and internal heating is used. Different storms required different magnitudes of radial diffusion and internal heating and the relative contributions of these two acceleration mechanisms varied from storm to storm. A comparison of the results from different runs for the four storms and an analysis of the larger than expected radial diffusion coefficients further suggests that internal heating contributes more to the enhancement of 2.7 MeV electrons at L=4 than radial diffusion.
SM21A-1679
Rayleigh-Taylor type Instability in auroral patches
Based on narrow-field-of-view camera observations of patchy auroral structures during substorm recovery phase, we found finger-like structures with a scale size of ~5-25 km at the western boundary of the auroral patches. The observations were made during the THEMIS satellites - ground auroral campaign at Gillam (56.4N, 265.4E), Canada, for January 2-16, 2008. We suggest that the finger-like structures are caused by macroscopic Rayleigh-Taylor type plasma instability arising in the magnetospheric equatorial plane due to force balance between (eastward) magnetic tension force and (westward) pressure gradient force. The instability can be the cause of structuring of diffuse aurora into patches.
SM21A-1680
Polarization analysis of Pc 1 geomagnetic pulsations at multi-point ground observations at middle latitudes
Pc 1 geomagnetic pulsations propagate from the high-latitude source region to middle latitudes in the ionosphere. The high-latitude source region links to the magnetosphere where ion cyclotron instability occurs around the plasmapause. Since Pc 1 pulsation observed by ground magnetometers at middle latitudes can be a mixture of waves from several high-latitude source regions, the polarization analysis of Pc 1 pulsations enables us to understand the spatial structure and time variations of the high-latitude source region. In order to investigate spectral and propagation characteristics of the Pc 1 at mid-latitudes, we have installed three induction magnetometers at Paratunka (PTK, 53.0N, 158.2E, magnetic latitude (MLAT): 45.8N), Moshiri (MSR, 44.4N, 142.3E, MLAT: 35.7N) and Sata (STA, 31.0N, 130.7E, MLAT: 22.0N). The observations with a 64-Hz sample recording have been started on July 5, 2007, at MSR, on August 21, 2007, at PTK, and on September 5, 2007, at STA and will be started at Magadan (MGD, 59.7N, 151.0E, MLAT: 50.6N) on November 2008. Polarization analysis with these multi-point data indicates that the Pc 1 polarization directions on November 11, 2007 depend on frequency with a difference of ~30 degree. For December 17, 2007 event, the polarization angle varies in time for ~30 deg/hour. These facts may indicate either the structure and motion of the high-latitude Pc 1 source region or the effects of the duct propagations in the inhomogeneous ionosphere. In this presentation, we also show the statistical results of these polarization analyses using 1-year data of middle latitude Pc 1 observations.