Selected Abstracts

We present observations of 1116 current sheet crossings in the Martian magnetotail during one Martian year, as identified from magnetic field rotations measured by Mars Global Surveyor (MGS) at 400 km altitude and 2 am local time. Crossings are observed everywhere except above strong crustal fields, and many occur in clusters, with preferred locations varying as a function of season and IMF draping direction. Magnetic polarities are consistent with day-side IMF draping directions and a two-lobe induced magnetotail. Energetic "plasma sheet" electrons are often absent, implying that currents can be carried by ions or low energy electrons, with thicknesses of <~100 km arguing for electrons. The presence of a thin current sheet at low altitudes, with specific seasons and IMF directions favored for some geographic locations, implies that reconnection between crustal fields and the draped IMF may play an important role in its formation and location.

The dayside magnetosphere responds directly to the incident interplanetary magnetic field (IMF) and solar wind energy. Changes in the IMF and solar wind drive changes in magnetospheric and ionospheric convection. Currents and (in the case of upward currents) aurora respond to these changes. Therefore, the dayside aurora is also a direct indicator of how the magnetosphere responds to IMF and solar wind energy input. Recent observations from space-based auroral imagers have shown hemispheric asymmetries in the morphology and temporal behavior of the dayside aurora. This suggests that asymmetries also exist in the solar wind-magnetosphere energy transfer processes that give rise to the auroral emissions. Since the dayside aurora allows us to monitor the response of the magnetosphere to the IMF and solar wind input, observing dayside aurora in both hemispheres allows us to monitor the asymmetric response of the magnetosphere. Using global auroral images from Polar UVI in the southern hemisphere and IMAGE FUV in the north, we analyze asymmetries in the dayside aurora. The observed asymmetries are related to changes in the IMF and solar wind. The IMF plays a major role in influencing the asymmetrical behavior of the dayside aurora. When the IMF is southward and a significant dawnward component exists, there is an enhancement in the afternoon aurora in the northern hemisphere. If the IMF has a significant duskward component, then an enhancement in the afternoon aurora in the southern hemisphere is observed. When |B_Y/B_Z| is greater than about 2, distinct structure (i.e., a string of pearls configuration) is seen in the hemisphere with enhanced emission. In addition to asymmetries observed during periods of quasi-steady energy input, asymmetries in the dayside aurora are also observed during large scale changes in the IMF and solar wind. The results of this work will lead to new insights into how the dayside aurora, thus the dayside magnetosphere, responds asymmetrically to the solar wind driver.

We investigate the effect of ionization due to electron precipitation on the electron density and total electron content (TEC) in the nightside ionosphere of Mars. As input we use recently reported auroral-like peaked electron spectra that appear to have undergone an acceleration process. The nominal electron density in the nightside ionosphere is very low, so the electron precipation creates a significant increase in the TEC. The regions of ionization are localized in space and correspond to magnetic cusps formed by the interaction of the Martian crustal sources with the interplanetary magnetic field. The most energetic accelerated spectra, hence the largest nightside elecron densities and TECs, appear correlated with solar energetic particle (SEP) events and may represent a previously unknown SEP effect at Mars. The horizontally inhomogeneous regions of ionization will likely distort radio waves used for orbit-to-surface communication and for precise positioning calculations on the nightside of Mars which have not previously been taken into account.

The dayside magnetosphere responds directly to the incident interplanetary magnetic field (IMF) and solar wind energy. Changes in the IMF and solar wind drive changes in magnetospheric and ionospheric convection. Currents and (in the case of upward currents) aurora respond to these changes. Therefore, the dayside aurora is also a direct indicator of how the magnetosphere responds to IMF and solar wind energy input. Recent observations from space-based auroral imagers have shown hemispheric asymmetries in the morphology and temporal behavior of the dayside aurora. This suggests than asymmetries also exist in the solar wind-magnetosphere energy transfer processes that give rise to the auroral emissions. Since the dayside aurora allows us to monitor the response of the magnetosphere to the IMF and solar wind input, observing dayside aurora in both hemispheres allows us to monitor the asymmetric response of the magnetosphere. Using global auroral images from Polar UVI in the southern hemisphere and IMAGE FUV in the north, we analyze asymmetries in the dayside aurora. The observed asymmetries are related to changes in the IMF and solar wind. The IMF plays a major role in influencing the asymmetrical behavior of the dayside aurora. When the IMF is southward and a significant dawnward component exists, there is an enhancement in the afternoon aurora in the northern hemisphere. If the IMF has a significant duskward component, then an enhancement in the afternoon aurora in the southern hemisphere is observed. When |B_Y/B_Z| is greater than about 2, distinct structure (i.e., a string of pearls configuration) is seen in the hemisphere with enhanced emission. In addition to asymmetries observed during periods of quasi-steady energy input, asymmetries in the dayside aurora are also observed during large scale changes in the IMF and solar wind. The results of this work will lead to new insights into how the dayside aurora, thus the dayside magnetosphere, responds asymmetrically to the solar wind driver.

Auroral emission has been detected at every planet in the solar system which has a known global magnetic field and a substantial atmosphere. Recent Mars Express observations have shown that auroral emission also exists on Mars, which lacks a global magnetic field but does have localized regions of strong magnetic crustal sources. Additionally, accelerated electron spectra, reminiscent of those observed in Earth's auroral region, have recently been found in data from Mars Global Surveyor. These recent developments have prompted us to revisit the question of auroral emission on Mars. Previous calculations of auroral emission on Mars have neglected the effects of strong magnetic field gradients associated with converging fields near localized crustal sources. Also, previous calculations used typical sheath or tail electron spectra rather than the newly discovered accelerated spectra. We use observed MGS electron spectra as input into a new coupled electron transport and emission model which includes realistic magnetic field gradients. We analyze the effect the strong gradients have on the electron intensity in the upper atmosphere and the resulting excitation and ionization rates and emissions. In addition, we explore the range of excitation and ionization rates and emissions due to the different classes of observed electron spectra from sheath-like, to highly accelerated, to those observed during solar energetic particle events.

Based on imaging data from the Polar VIS Earth camera and the IMAGE-FUV instruments we have documented how the IMF orientation and the dipole tilt angle act as the main and the secondary controlling factors of the relative displacement of the aurora in the conjugate hemispheres. Comparing our results with the asymmetries predicted by recent empirical magnetospheric models, we show that the assumed partial penetration of the IMF into the magnetosphere is clearly supported by observations, but the modeled conjugate shifts were found to be an order of magnitude smaller than the observed ones.

In the near Earth plasma sheet, the three dimensional plasma and energetic particle investigation (3DP) on the Wind spacecraft has detected very rapid (< 1 second) changes in the electron distributions. The changes generally consist of a transition from a relatively high density, low temperature distribution to a low density, higher temperature distribution. These changes coincide with intervals of large magnetic field fluctuations, large ion velocity moments, and increases in the flux of energetic particles. The goal of this work is to determine whether the electrons are accelerated in situ or if two distinct electron populations are being sampled as the boundary between them is swept by the spacecraft. First results indicate that the change in the electron distributions is nonadiabatic in both the thermodynamic sense, i.e., the specific entropy is not constant, and in the kinetic sense: the first adiabatic invariant is not conserved. Since changes in the magnetic field coccur on timescales much longer than the electron gyroperiod, one would expect that for a local acceleration process the first adiabatic invariant would be conserved in the absence of invariant breaking processes such as wave-particle interactions. Although we cannot rule out nonadiabatic in situ acceleration, the simplest interpretation is that the electrons are accelerated elsewhere and transported to the observation point with the boundary between the ambient and accelerated electrons passing over the spacecraft in less than one second.

Using global auroral images from Polar UVI in the southern hemisphere and IMAGE FUV in the north, we have analyzed the asymmetries in the dayside aurora for a five-month period. The observed asymmetries were related to the interplanetary magnetic field (IMF). Initial results suggest that the direction of the IMF plays a major role in influencing the asymmetrical behavior of the dayside aurora. When the IMF is southward and a significant dawnward component exists, there is an enhancement in the afternoon aurora in the northern hemisphere. If there is a significant duskward component to the IMF, then an enhancement in the afternoon aurora in the southern hemisphere is observed. Additionally, when the ratio of the magnitudes of the Y and Z components of the IMF are greater than about 2, distinct structure (i.e., a string of pearls configuration) is seen in the hemisphere with enhanced emission. These results are in general agreement with models and observations of the IMF influence on ionospheric convection. A strong Y component of the IMF can lead to a strong shear flow at the dayside convection reversal boundary. Strong flow shear can lead to strong field aligned currents (i.e., elelctron precipitation for upward current) in this same region. If the flow shear exceeds some threshold, an instability (e.g., a Kelvin-Helmholtz instability) can develop leading to discrete structures.

Using ultraviolet images from two global auroral imagers, IMAGE FUV in the northern hemisphere and Polar UVI in the south, we present the first synoptic scale conjugate observations of the dayside aurora. We find that the morphology of the afternoon aurora is significantly different in the two hemispheres. Multiple spots in a "string of pearls" configuration are seen in the southern hemisphere while the northern aurora is unstructured. We relate the observed asymmetry in the aurora to the Y GSM component of the IMF: a strong IMF B_Y modifies the ionospheric convection and field aligned current patterns, leading to the auroral asymmetry. Additionally, we suggest that the instability giving rise to the multiple spot morphology occurs at low altitude.

Using global ultraviolet auroral images from both Polar and IMAGE satellites, we investigate the conjugacy of afternoon aurora. This study is limited to periods between the equinox and northern winter solstice when Polar UVI is imaging the southern auroral zone and IMAGE FUV provides coverage of the northern auroral region. Both instruments are sensitive to LBH emissions produced by electron impact. We find several intervals during which the dayside auroral morphology is not conjugate: multiple spots aligned in longitude in one hemisphere are absent in the other. Hence, the electron access or electron acceleration mechanisms responsible for the auroral emission are likewise not conjugate. The asymmetries in the auroral morphology are related to the direction of the y-component of the IMF. When IMF By is strongly negative (positive), the afternoon aurora is more structured and discrete in the northern (southern) hemisphere. The characteristics of the multiple spots are consistent with them being the result of a Kelvin-Helmholtz instability (KHI). This implies that the KHI may only be operating in one hemisphere.

We compare the open flux content of the magnetosphere, quantified by measurements of the size of the northern ionospheric polar cap, with the radius of the magnetotail at X ~ -25 R_E, deduced from observations made by the IMP-8 spacecraft. During an 8 hour period of observation we estimate that the proportion of terrestrial flux that is interconnected with the solar wind varies between 12 and 2.5%. This latter extreme, representing an almost closed magnetosphere, follows the incidence of a solar wind dynamic pressure step, the onset of a large substorm, and a three hour period of northward IMF. The deflated and compressed magnetotail is predicted to have a radius as small as 12 R_E at this time. The magnetotail does not re-inflate to more typical dimensions until some time after a southward turning of the IMF, leading to accumulation of open flux through low latitude reconnection. We compare our observations with estimates of the shape of the magnetopause from an empirical model. We also present a simple model of the varying length of the magnetotail, based on upstream solar wind conditions, and observations of the size of the polar cap.

Because the Earth's magnetic field is largely dipolar and symmetric, many auroral features are conjugate between the northern and southern hemispheres. However, previous work has shown that the aurora can be nonconjugate. Most previous optical conjugacy studies have been limited to ground based observations or ground based and space based imager comparisons. In both cases at least one observation point is restricted to viewing only small scale features. Conjugate observations of the large scale behavior of the aurora have been confined to rare, serendipitous space based imager conjunctions and single spacecraft viewing of both hemispheres which is tempered by large oblique viewing angles. As the Polar spacecraft's apogee has descended in the the southern hemisphere, the Polar Ultraviolet Imager (UVI) has spent an increasing amount of time viewing the southern aurora. Simultaneously, the Wideband Imaging Camera (WIC) onboard the IMAGE spacecraft has been observing the northern aurora. By using image data from both spacecraft, we are able to systematically analyze the degree of auroral conjugacy on synoptic scales and over a wide variety of geomagnetic conditions. In this work, we focus on the conjugacy of the region of intense auroral emission during substorm onset and expansion. We find a persistent displacement in local time of the region of active aurora during substorm expansion; features in the northern hemisphere are shifted westward (duskward) relative to the conjugate point of the southern hemisphere aurora by up to a few thousand kilometers. Often there is a shift in the opposite direction observed before and at substorm onset. The same sense of displacement has been reported in earlier work. The sense or magnitude of the displacement showns no obvious correlation with the interplanetary magnetic field orientation or strength as suggested in previous studies. Therefore, we suggest that the displacement in local time of the region of intense auroral emission is a result of the asymmetric distortion of the magnetic field by the large scale field-aligned currents associated with substorms.

Chen, L.-J., A. Bhattacharjee, K. Sigsbee, G. Parks, M. Fillingim, and R. Lin (2003), Wind observations pertaining to current disruption and ballooning instability during substorms, Geophys. Res. Lett., 30(6), 1335, doi:10.1029/2002GL016317.

The westward propagation of wave disturbances associated with current disruption is observed in the near-Earth plasma sheet by the Wind satellite. By analyzing the time delay between earthward and tailward flux enhancements of energetic ions, the propagation velocity is estimated to be several hundred kilometers per second. A large anisotropy between the duskward and dawnward fluxes of energetic ions is observed to persist until the local onset of a current disruption. This anisotropy is consistent with an earthward density gradient which is significantly reduced after the magnetic fluctuations that accompany the current disruption cease. The reduction process is impulsive and bursty, suggesting that the underlying dynamics is nonlinear. The westward propagation of the unstable wave disturbances, the radial density gradient and its subsequent reduction support the drift ballooning instability as a possible mechanism for triggering substorms.

Fillingim, M. O., G. K. Parks, R. P. Lin, S. D. Bale, and L.-J. Chen, Observations of bi-directional field aligned electrons and solitary waves in the plasma sheet, presented at the 2003 EGS-AGU-EUG Joint Assembly, Nice, France, April 6 - 11, 2003.

Observations of narrowly collimated field aligned bi-directional electron distributions measured by the WIND spacecraft in the plasma sheet at radial distances of 10 to 20 Earth radii in the midnight sector are presented. At energies below about 1 keV, the parallel flux is about one order of magnitude larger than the perpendicular flux. At higher energies up to 30 keV, the anisotropy is much smaller, closer to a factor of 2. Typically the distributions are flat-topped; however, occasionally well defined counter streaming electron beams are observed. Through out these time intervals, magnetic field mapping suggests that the footprint of WIND is in the region of intense auroral emission as indicated by Polar/UVI images. The beams are inferred to be of ionospheric origin. Coincident with the field aligned electron observations, plasma wave measurements show the presence of solitary structures. We suggest that the presence of counter streaming electron beams and their mutual interactions are responsible for the generation of the observed solitary structures.

Fillingim, M. O., G. K. Parks, Y.-K. Tung, M. Wilber, T. Immel, and S. B. Mende, The conjugacy of dayside auroral electron precipitation, presented at the 2003 Yosemite Conference-Workshop: The Dayside Magnetopause and Cusp, Yosemite National Park, CA, Februrary 9 - 13, 2003.

Using global auroral images from both Polar and IMAGE satellites, we investigate the conjugacy of dayside aurora. This study is limited to periods between the equinox and northern winter solstice when Polar UVI is imaging the southern auroral zone and IMAGE FUV provides coverage of the northern auroral region. Both instruments are sensitive to LBH emissions produced by electron impact. We find several intervals during which the dayside auroral morphology is not conjugate in either space or time. Hence, the electron access or electron acceleration mechanisms responsible for the auroral emission are likewise not conjugate. Preliminary results indicate that periods of non-conjugacy may be related to large changes in the y-component of the IMF. Additionally, asymmetries in the ionospheric conductivity, especially closer to the solstice, may also contribute to the observed non-conjugacy. By comparing the morphologies of the electron precipitation in both the northern and southern dayside auroral regions, we can gain insight into solar wind-magnetosphere energy flow and coupling, and provide a valuable test for present modeling efforts.

Fillingim, M., G. Parks, R. Lin, M. Wilber, C. Carlson, D. Chua, and L. Peticolas, Counter-streaming electron beams in the plasma sheet associated with auroral activity, abstract SM21B-0535, presented at the 2002 AGU Fall Meeting, San Francisco, CA, December 6 - 10, 2002.

Electron observations by the WIND plasma instruments in the near-Earth plasma sheet (at a radial distance of about 10 Earth radii) during a substorm expansion and recovery reveal the presence of counter-streaming electron beams. The beams, which appear shortly after large fluctuations in the magnetic field, are centered at about 1 keV and are confined to pitch angles less than about 10 degrees. These beams appear to be unstable and rapidly decay resulting in bi-directional field-aligned electron distributions. The resulting distributions contain two components: a thermal, relatively isotropic plasma sheet component, and a lower energy, more strongly field-aligned beam remnant. The bi-directional field-aligned distributions are observed for more than one hour. Simultaneous FAST plasma measurements near the magnetic footprint of WIND in the auroral region show a similar two component electron spectrum. The source of the field-aligned beams is unknown, but based on the narrowness of the beams in the plasma sheet, we contend that the source is at low altitude and that the source mechanism is related to the auroral acceleration processes.

Fillingim, M. O., G. K. Parks, R. P. Lin, M. McCarthy, and A. Szabo (2003), Observations of magnetospheric disturbances during auroral activity, in Disturbances in Geospace: The Storm-Substorm Relationship, Geophys. Monogr. Ser., vol. 142, edited by S. A. Sharma, Y. Kamide, and G. S. Lakhina, pp. 45-54, AGU, Washington, D.C.

We present high time resolution plasma and magnetic field data from the near-Earth plasma sheet during times of active aurorae. The plasma sheet disturbance associated with the auroral activity is composed of Earthward traveling ions with large mean velocities (<v> = § v f(v) d³v) and large amplitude, high frequency magnetic field fluctuations. The ion <v> can change substantially (by up to 100%) on time scales comparable to the local proton gyroperiod. The magnetic fluctuations lead to large, rapidly varying induced electric fields. Power spectral analysis of the magnetic field data shows a significant amount of wave power is present at frequencies up to and greater than the local proton cyclotron frequency. Examination of the three-dimensional ion distribution functions indicates that the distributions are complex and nongyrotropic, with large gradients and anisotropies, and dynamic, with considerable changes in the phase space features within one gyroperiod. These results illustrate that kinetic physics controls the plasma behavior during times of plasma sheet disturbances associated with auroral activity. This conclusion is in contrast to the usual intrepretation that the large ion velocity moments observed during plasma sheet disturbances are convective in nature (i.e., bursty bulk flows). Additionally, we show that these kinetic effects are important in the near-Earth plasma sheet over a wide range of geomagnetic activity, from pseudobreakups to substorms. Therefore, we suggest that these kinetic processes operate during all types of geomagnetic disturbances and can occur throughout large regions of the magnetotail during substorms and storms.

Fillingim, M. O., G. K. Parks, D. Chua, and R. P. Lin (2002), Comparison of plasma sheet and auroral electron energy fluxes during substorms, Proc. 6th International Conference on Substorms, University of Washington, 382-387.

Using both global auroral images and in-situ particle measurements, we quantitatively compare the downgoing electron energy flux in the plasma sheet with the electron energy flux into the auroral ionosphere with respect to substorm phase. We find that during quiet times, the downgoing energy flux in the plasma sheet mapped down to ionospheric altitudes is comparable to the energy flux observed in the aurora. During intervals of intense auroral emission such as substorm onset and expansion, the electron spectra in the conjugate region of the plasma sheet harden, increasing the downgoing energy flux. However, the increase in the plasma sheet energy flux is not enough to account for the increased energy flux into the ionosphere by up to an order of magnitude. This is consistent with the idea that additional energy flux is entering the loss cone through the presence of parallel electric fields above the ionosphere during intervals of intense auroral emission. As auroral activity decreases during recovery, the downgoing plasma sheet electron energy flux nearly sufficiently accounts for the diffuse auroral luminosity. Our results show that although large changes in the plasma sheet electron distributions occur at substorm onset, lower altitude processes are dominant in producing the observed auroral energy flux. These low altitude processes decrease in importance throughout the recovery phase.

Fillingim, M. O., G. K. Parks, D. Chua, and R. P. Lin, Comparison of plasma sheet and auroral electron energy fluxes during substorms, presented at the 6th International Conference on Substorms, Seattle, WA, March 25 - 28, 2002.

Using both global auroral images and in-situ particle measurements, we quantitatively compare the downgoing electron energy flux in the plasma sheet with the electron energy flux into the auroral ionosphere with respect to substorm phase. We find that during quiet times, the downgoing energy flux in the plasma sheet mapped down to ionospheric altitudes is comparable to the energy flux observed in the aurora. During intervals of intense auroral emission such as substorm onset and expansion, the electron spectra in the conjugate region of the plasma sheet harden, increasing the downgoing energy flux. However, the increase in the plasma sheet energy flux is not enough to account for the increased energy flux into the ionosphere by up to an order of magnitude. This is consistent with the idea that additional energy flux is entering the loss cone through the presence of parallel electric fields above the ionosphere during intervals of intense auroral emission. As auroral activity decreases during recovery, the electron distributions in the plasma sheet become strongly field aligned up to energies of several keV. The downgoing plasma sheet electron energy flux nearly sufficiently accounts for the diffuse auroral luminosity. Our results show that although large changes in the plasma sheet electron distributions occur at substorm onset, lower altitude processes are dominant in producing the observed auroral energy flux. These low altitude processes decrease in importance throughout the recovery phase.

Fillingim, M. O. (2002), Kinetic Processes in the Plasma Sheet Observed during Auroral Activity, Ph.D. Thesis, University of Washington.

In this dissertation we analyze plasma sheet magnetic field and plasma data observed during varying levels of auroral activity from very small, isolated events known as pseudobreakups to large, global events known as substorms. The plasma and magnetic field data are taken from instruments onboard the WIND spacecraft while it traverses the near-Earth plasma sheet. Simultaneous global auroral images from POLAR/UVI allow us to determine the auroral activity level. The goal of this dissertation is to provide the most complete set of plasma sheet observations during auroral activity currently available. The kinetic aspects of the plasma dynamics which have largely been ingnored in other works are emphasized here. We have the capability to resolve changes in the three dimensional ion distribution functions with a time resolution comparable to or faster than the local ion gyroperiod. In addition, we consider the typically neglected electron dynamics when relating plasma sheet processes to the aurora. We find that the plasma sheet signatures of both pseudobreakups and substorms appear very similar. During both types of events, increases in auroral precipitation into the ionosphere are associated with large amplitude, high frequency magnetic field fluctuations, large Earthward ion <v>, increases in the fluxes of high energy ions and electrons, and hardening of the electron spectrum. Both ion and electron distributions appear to be composed of multiple components. Electromagnetic waves with power at frequencies up to and above the local proton gyrofrequency area also observed. Additionally, the ion distributions can change significantly in one gyroperiod. Together, these results imply that the microphysical processes occurring in the plasma sheet during pseudobreakups and substorms are the same and that kinetic effects are important. Therefore, magnetohydrodynamics (MHD) cannot adequately describe the physics occurring during large ion <v> events.

Parks, G. K., L. J. Chen, M. Fillingim, R. P. Lin, D. Larson, and M. McCarthy (2002), A new framework for studying the relationship of aurora and plasma sheet dynamics, J. Atmos. Terrestr. Phys., 64(2), 115-124.

Auroras have been extensively studied using images obtained by space-borne experiments. We use global UVI images obtained from Polar and simultaneous plasma data obtained by the 3D instrument on Wind for the near-earth plasma sheet to study the dynamics of auroras with different size and intensity. Unstable phase space distributions are detected in the plasma sheet under diverse geomagnetic and solar wind IMF conditions (positive and negative B_z) and at all phases of a substorm. These results indicate that a plasma instability process with different disturbance levels operates in the plasma sheet and produces a continuum of auroral size and intensity. The criteria for triggering the instability are dependent on the local properties of the plasma distributions. These observations suggest a new framework to integrate previous and current results and a new way to examine the causal relationship of auroral and plasma sheet dynamics.

Fillingim, M. O., G. K. Parks, D. Chua, G. A. Germany, R. P. Lin, and M. McCarthy, Quantitative comparison of measured plasma sheet electron energy flux and remotely sensed auroral electron energy flux abstract SM51A-0789, presented at the 2001 AGU Fall Meeting, San Francisco, CA, December 10 - 14, 2001.

In situ plasma sheet observations and auroral images give us two views of magnetospheric dynamics. With in situ observations, we get a detailed point measurement; auroral images give us a global view. Previous studies have shown an excellent correlation between dynamic plasma behavior in the plasma sheet and auroral activity. Here we extend the previous work with quantitative comparisons between the two regions. We directly compare the electron energy flux measured in the plasma sheet with the electron energy flux into the ionosphere inferred from auroral images. We find that during quiet times, the plasma sheet is able to supply the aurora with nearly all of the observed energy flux. During intervals of intense auroral emission, the electron spectrum in the conjugate region of the plasma sheet changes, increasing the amount of energy flux incident on the ionosphere. However, the increases in the plasma sheet energy flux is not enough to account for the inferred energy flux into the ionosphere from the images by nearly an order of magnitude. This implies that additional energy flux must be entering the loss cone through pitch angle diffusion or through the presence of parallel electric fields between the plasma sheet and the ionosphere during intervals of intense auroral emission. A likely source of this additional energy flux is the low altitude auroral acceleration region.

Fillingim, M. O., G. K. Parks, L. J. Chen, M. McCarthy, J. F. Spann, and R. P. Lin (2001), Comparison of plasma sheet dynamics during pseudobreakups and expansive aurorae, Phys. Plasmas, 8(4), 1127-1132.

Global auroral images and plasma sheet ion distributions and magnetic field data are examined for two intervals when the Ultraviolet Imager (UVI) onboard the Polar spacecraft was imaging the entire northern auroral oval and, at the same time, the Wind spacecraft was passing through the near-Earth plasma sheet. On July 26, 1997, UVI recorded a series of brief, localized auroral brightenings known as pseudobreakups. On March 27, 1996, UVI observed several global expansions of auroral activity. Large variations in the magnetic field were observed by the Wind magnetometer, large velocity moments were derived from Wind ion measurements, and ions were accelerated the MeV energies during both types of activity. The plasma sheet dynamics appear very similar during these two different types of auroral activities. Closer inspection of the ion distribution functions and energy spectra indicate that the plasma sheet dynamics need to be characterized kinetically.

Parks, G. K., J. L. Chen, D. Chua, M. Fillingim, M. McCarthy, and R. P. Lin, New observations and interpretation of magnetospheric disturbances during substorms and storms, presented at the AGU Chapman Conference: Storm-Substorm Relationship, Mumbai, India, March 12 - 16, 2001.

Major magnetospheric energy depostion into the ionosphere occurs primarily during substorms and storms. We present new results of a systematic study of substorms and storms that include various global auroral forms and simultaneous plasma measurements made in the near earth geomagnetic tail. This study reveals that the dynamics of the magnetosphere consists of a continuum of disturbance scale sizes and intensity levels. These disturbances accelerate ions (electrons) to MeV (hundreds of keV) energies, occur at various phases of substorms and even during relatively quiet periods of northward IMF. The criteria for triggering these magnetospheric disturbances appear to depend only on the local plasma properties existing in the magnetosphere. The actual mechanism responsible for the trigger is not yet known, but data show that magnetic field variations have /\B/B >> 1, indicating nonlinear processes are active. Power spectral estimates further indicate that substantial power exists up to the local ion cyclotron frequency and beyond indicating kinetic physics is required for understanding these observations.

Parks, G. K., L. J. Chen, M. Fillingim, and M. McCarthy (2001), Kinetic characterization of plasma sheet dynamics, Space Sci. Rev., 95(1-2), 237-255.

The Wind spacecraft made 26 perigee passes through the near-earth plasma sheet region during 1994 to 1997. Nearly all of these passes obtained plasma data from substorm and bursty bulk flow (BBF) events. New features of ion distributions have been observed in both the plasma sheet boundary layer (PSBL) and the central plasma sheet (CPS) in the vicinity of the current sheet that are relevant for understanding the structure of the PSBL and the mechanisms of particle acceleration to MeV energies associated with the BBF events. Kinetic processes are key to understanding these new observations that are not adequately explained by existing magnetohydrodynamics (MHD) models and theories. This article will feature the phase space distribution functions as the primary data product. The main purpose of this article is to establish an observational framework for new improved models and theories. The new observations should challenge modelers and theorists.

Fillingim, M. O., G. K. Parks, M. McCarthy, R. P. Lin, and A. Szabo, Plasma sheet variations observed on kinetic timescales, abstract SM71A-06, presented at the 2000 AGU Fall Meeting, San Francisco, CA, December 15 - 19, 2000.

We examine high-time resolution plasma and magnetic field data from WIND perigee passes through the near-Earth plasma sheet during auroral events associated with high earthward ion velocity moments. Full 3-D ion and electron distributions are obtained every 3 seconds, and the magnetic field is sampled every 46 milliseconds. Variations in the plasma distributions and moments occur on timescales on the order of the local proton gyroperiod. The ion velocity moment typically changes by over 100 km/s from one 3-second distribution to the next. Averaging over several distributions smears out these variations and yields lower velocity moments. The magnetic field changes in direction and magnitude on timescales faster than the proton gyroperiod with dB/dt reaching values in excess of 30 nT/s. Magnetic field power spectra indicate that there can be significant wave power at frequencies on the order of the local proton gyrofrequency consistent with particle results. These results highlight the importance of high-time resolution plasma measurements to properly describe dynamic velocity moment events in the plasma sheet associated with aurora. The timescales of the observed fluctuations are much faster than convection timescales that are usually considered when discussing plasma sheet dynamics. Ours study shows that kinetic processes are determining the plasma sheet dynamics.

Parks, G., M. Brittnacher, D. Chua, M. Fillingim, G. Germany, and J. Spann (2000), Behavior of the aurora during 10-12 May 1999 when the solar wind nearly disappeared, Geophys. Res. Lett., 27(24), 4033-4036.

The aurora was still active with occasional pseudobreakup events when the solar wind density diminished to unusually small densities (0.2 cm^-3) during May 10-12, 1999. The aurora was observed at high magnetic latitudes indicating that the electron precipitation source moved northward as the geomagnetic activity decreased. The events we have studied indicate that the solar wind density alone is not the primary parameter that controls the auroral activity. The weak auroral activity was observed with 150 nT magnetic bays and when the interplanetary magnetic field (IMF) B_Z was small and positive resulting in small epsilon parameter. A new auroral feature was observed on May 11, 1999, between 0900-2000 UT. The electron precipitation was energetic, uniform, and covered the region commonly identified as the polar cap. This precipitation lasted for more than 10 hours and was stable over time scales of tens of minutes. On May 12, as the solar wind began to recover, a prolonged period of dayside activity occurred and was followed by a typical aurora at 0500 UT.

Brittnacher, M., M. Wilber, M. Fillingim, D. Chua, G. Parks, J. Spann, and G. Germany (2000), Global auroral response to a solar wind pressure pulse, Adv. Space Res., 25(7-8), 1377-1385.

A global intensification of the aurora was observed by the Ultraviolet Imager on the NASA Polar spacecraft in conjunction with the arrival of the sheath from a solar coronal mass ejection. The aurora was first observed to brighten on the dayside and then the intensification progressed rapidly toward the nightside. During this time the IMP-8 spacecraft in the solar wind recorded a 35-minute period of increased solar wind dynamic pressure. A small substorm (or, possibly pseudobreakup) occurred within a minute of the arrival of the auroral intensification on the nightside in conjunction with a second peak in the dynamic pressure. We propose that the intensification of the aurora can be explained on the basis of the compression of the magnetopause and the generation of hydromagnetic waves by the rapid increase in the solar wind dynamic pressure. It is also evident that the substorm was triggered by waves, generated by a second rise in the dynamic pressure, that propagated to flux tubes connected to the premidnight auroral region.

Parks, G. K., L. J. Chen, M. Fillingim, and M. McCarthy (2000), Plasma behavior during pseudobreakup and expansive aurorae, Proc. 5th International Conference on Substorms, ESA SP-443, 235-242.

Pseudobreakup and aurorae with expansive phases are considered different auroral forms in that the former is small scale and the electron precipitation is short lived while the latter starts out small but expands to cover a large region of the nightside auroral oval and the electron precipitation activity lasts for tens of minutes. We have studied the plasma distributions of ions measured by the Wind spacecraft in the plasma sheet when these auroral forms were identified by the UVI on Polar. We find that the plasma ion distributions associated with these auroral forms behave nearly identically, suggesting that the process that initiates the electron precipitation is similar. However, observations have not yet revealed information on how the dynamics operate to lead the small scale precipitation into global scale precipitation.

Fillingim, M. O., G. K. Parks, L. J. Chen, M. Brittnacher, G. A. Germany, J. F. Spann, D. Larson, and R. P. Lin, Ion signatures of pseudobreakups and expansive auora i the magnetotial, presented at the 2000 GEM Summer Workshop, Snowmass, CO, June 19 - 23, 2000.

We present plasma distributions measured by the WIND spacecraft during two perigee passes through the near-Earth plasma sheet region. During the first interval (26 July, 1997) Polar UVI observed a series of pseudobreakups, characterized by localized, short-lived auroral brightenings. Two large auroral expansions were observed by UVI during the second interval (27 March, 1996). WIND plasma measurements revealed large ion velocity moments associated with large fluctuations in the magnetic field. Large <V> were observed during all types of auroral activity. The plasma distributions indicate that the large ion velocity moments are not due to flows in the fluid sense, but are the result of complex ion dynamics.

Fillingim, M. O., G. K. Parks, L. J. Chen, M. Brittnacher, G. A. Germany, J. F. Spann, D. Larson, and R. P. Lin (2000), Coincident POLAR/UVI and WIND observations of pseudobreakups, Geophys. Res. Lett., 27(9), 1379-1382.

Using POLAR/UVI global images, we have identified a period of successive minor auroral activations during which WIND was making a perigee pass (X ~ 11 R_E). These auroral brightenings are interpreted to be pseudobreakups due to the lack of global expansion. Large magnetic field fluctuations and high earthward ion velocity moments measured by the WIND spacecraft show a nearly one-to-one correspondence with the auroral intensifications. Analysis of the plasma parameters indicates that there is no difference in the behavior or the plasma during pseudobreakups as compared to substorm expansive phase onset. Inspection of the ion distributions functions during high velocity moment events reveals the presence of a two component plasma. The particles contributing to the large mean velocities are energetic ions with energies from ~ 2 to 27 keV. We conclude that pseudobreakups are the ionospheric signature of high velocity moment events.

Fillingim, M. O., M. Brittnacher, G. K. Parks, L. J. Chen, G. A. Germany, J. F. Spann, and R. P. Lin, Magnetotail plasma signatures of pseudobreakups and substorms, abstract SM41B-20, presented at the 1999 AGU Fall Meeting, San Francisco, CA, December 13 - 17, 1999.

Using POLAR/UVI global images, we have identified a period of successive minor auroral activations during which WIND was making a perigee pass through the near-Earth magnetotail. On the basis of images, these auroral brightenings are interpreted to be pseudobreakups due to the lack of significant global expansion. Large magnetic field fluctuations measured by the WIND spacecraft show a nearly one-to-one correspondence with the auroral intensifications. During intervals of large field variations and auroral brightenings, energized ions have an Earthward velocity while the energized electrons generally remain isotropic. Closer inspection of the ion distribution functions indicate that the high velocity moments are not due to convective flows. Rather, the plasma is composed of a moving hot component and a stagnate cold component. We also trace the particles observed by WIND backwards in time to determine the source regions for the particles. Based upon these observations, we find that to zeroth order there is no difference in the behavior of the plasma during pseudobreakups as compared to substorm expansive phase events.

Brittnacher, M., M. Fillingim, G. Parks, G. Germany, and J. Spann (1999), Polar cap area and boundary motion during substorms, J. Geophys. Res., 104(A6), 12,251-12,262.

The area of the polar cap as a function of local time and substorm phase was measured using images from the Polar Ultraviolet Imager (UVI) for different interplanetary magnetic field (IMF) orientations during three substorms in January 1997. We measured changes in the polar cap area and motion of the poleward and equatorward boundary of the auroral oval as determined by UVI images. It was found that the polar cap boundary is strongly influenced by thinning of the oval, decrease in polar cap structures, the poleward expansion of the substorm at midnight and the fading luminosity below the instrument sensitivity threshold. Generally these effects dominate over the latitudinal motion of the auroral oval at its equatorward edge. A new feature is that the polar cap region clears of precipitation during the substorm growth phase which expands the size of the polar cap but may not necessarily be related to an expansion of the open flux. We present a new finding that the increase in polar cap area prior to onset and the decrease in the area following it are independent of the strength of the southward IMF component. For one case the polar cap increased while the southward component of the IMF was no less than 0+/-0.5 nT. These observations have strong implications for models that use the polar cap area to estimate the magnitude of energy storage in the lobe magnetic field and loss during substorms.

Fillingim, M. O., M. B. Moldwin, H. K. Rassoul, P. Parrish, M. F. Thomsen, and D. J. McComas (1999), Angular distributions of suprathermal electrons observed at geosynchronous orbit, J. Geophys. Res., 104(A3), 4457-4466.

Six months of low-energy electron plasma data collected using the Los Alamos National Laboratory magnetospheric plasma analyzer (MPA) onboard the geosynchronous satellite 1989-046 have been surveyed. The MPA instrument measures the three-dimentional energy per unit charge distributions of cold ions and electrons, allowing for the simultaneous determination of the angular distribution and ambient plasma regime. Suprathermal electrons in the energy range 15 to 200 eV were characterized by local time of occurance, angular distribution, and ambient plasma regime. Results indicate a local time dependence in angular distributions, with trapped distributions, i.e., enhanced fluxes of particles with pitch angles near 90^o and 270^o, primarily being observed in the morning, coincident trapped and field-aligned angular distributions (enhanced fluxes of particles with pitch angles near 90^o and 270^o coincident with enhanced fluxes of particles with pitch angles near 0^o and 180^o) occurring around noon, a lack of detectable low-energy electron fluxes near dusk, and a complex combination of angular distributions on the nightside. When both trapped and field-aligned angular distributions are present, the field-aligned component generally has lower energy than the trapped component. Dayside field-aligned angular distributions are interpreted as being photoelectrons fron the ionosphere, while trapped angular distributions are from the low-energy tail of the plasma sheet distribution. A plasma regime dependence in angular distributions was also observed. Plasma sheet angular distributions are generally isotropic or trapped. The plasma trough angular distributions are trapped or coincident trapped and field-aligned. Plasmaspheric electrons commonly have energies below our 15 eV threshold.

Fillingim, M. O., M. Brittnacher, G. K. Parks, G. A. Germany, J. F. Spann, and R. P. Lin, Coincident UVI and WIND observations of pseudo-breakups, abstract SM41B-16, presented at the 1998 AGU Fall Meeting, San Francisco, CA, December 6 - 10, 1998.

Using images taken by the Ultraviolet Imager (UVI) onboard the Polar spacecraft, we identify periods of pseudo-breakup activity coincident with perigee passes of the WIND spacecraft through the magnetotail. Previous studies have shown that from both observations on the ground and in the magnetotail there is very little difference phenomenologically between substorm onset and pseudo-breakups except for the degree of localization and the absense of global expansion. This raises the question of what prevents a pseudo-breakup from expanding globally. For the time intervals studied, we find a high correlation between pseudo-breakups and short-lived particle flux enhancements in the magnetotail. The velocity distribution of the plasma during some of these flux enhancements are indicative of bursty bulk flows. We suggest that the results imply that for these events the mechanism causing the bursty bulk flows may be manifested in the ionosphere as pseudo-breakups.

Fillingim, M. O., M. Brittnacher, G. K. Parks, G. A. Germany, and J. F. Spann, Solar wind-magnetosphere coupling influence on pseudo-breakup activity, presented at the 6th Huntsville Modeling Workshop, Guntersville, AL, October 26 - 30, 1998.

Pseudo-breakups are brief, localized auroral arc brightenings which do not lead to a global expansion historically observed during the growth phase of substorms. Previous studies have demonstrated that phenomenologically there is very little difference between substorm onsets and pseudo-breakups except for the degree of localization and the absence of a global expansion phase. A key open question is what physical mechanism prevents a pseudo-breakup from expanding globally. Using Polar/Ultraviolet Imager (UVI) images, we identify periods of pseudo-breakup activity. For the data analyzed, we find that most pseudo-breakups occur near local midnight, between magnetic local times of 21 and 03, at magnetic latitudes near 70 degrees, though this value may change by several degrees. While often discussed in the context of substorm growth phase events, pseudo-breakups are also shown to occur during prolonged relatively inactive periods. These quiet time pseudo-breakups can occur over a period of several hours without the development of a significant substorm for at least an hour after pseudo-breakup activity stops. In an attempt to understand the cause of quiet time pseudo-breakups, we compute the epsilon parameter as a measure of the efficiency of solar wind-magnetosphere coupling. It is noted that quiet time pseudo-breakups occur typically when epsilon is low; less than about 50 GW. We suggest that quiet time pseudo-breakups are driven by relatively small amounts of energy transferred to the magnetosphere by the solar wind insufficient to initiate a substorm expansion onset.

Fillingim, M. O., M. Brittnacher, R. K. Elsen, G. K. Parks, J. F. Spann, and G. A. Germany, Global auroral energy deposition derived from Polar UVI images, abstract SM41A-08, presented at the 1997 AGU Fall Meeting, San Francisco, CA, December 8 - 12, 1997.

Multipoint satellite and ground-based measurement of the transfer of energy and momentum from the solar wind to Earth's magnetosphere and ionosphere is one of the objectives of the ISTP program. Quantitative determination of the global energy deposition into the ionosphere from auroral electron precipitation can be derived from observations of the longer wavelength LBH band emissions made by the Ultraviolet Imager on the Polar spacecraft. These observations have a time resolution of approximately three minutes and are made continuously for up to 7 hours during apogee passes over the northern hemisphere during each 18 hour orbit. Assuming conjugacy of energy deposition between the two hemispheres, the total energy input to the ionosphere through electron precipitation can be determined at high time resolution. Previously, precipitating particle measurements along the tracks of low altitude satellites provided only local measurements, and the global energy precipitation could be inferred through models but not directly measured. We use the UVI images for the month of January 1997 to estimate the global energy deposition. We also sort the energy deposition into sectors to find possible trends, for example, on the dayside and nightside, or the dawn and dusk regions.

Fillingim, M. O. (1997), Characterization of 15 to 200 eV Electrons Observed at Geosynchronous Orbit, Masters Thesis, Florida Institute of Technology, Melbourne, FL.

Six months of electron plasma data collected using the Los Alamos National Laboratory Magnetospheric Plasma Analyzer (MPA) instrument onboard the geosynchronous satellite 1989-046 have been surveyed. Electrons in the energy range 15 to 200 eV were characterized by local time of occurance, pitch angle distribution(PAD), and ambient plasma regime. Results indicate a local time dependence in PADs, with trapped distributions primarily being observed in the morning, coincident trapped and field aligned PADs occuring around noon, a lack of detectable electrons fluxes near dusk, and a complex combination of PADs on the nightside. When both trapped and field aligned PADs exist, the field aligned component generally has lower energy than the trapped component. Dayside field aligned PADs are interpreted as being photoelectrons from the ionosphere, while trapped PADs are considered to be the low energy end of the plasma sheet. A plasma regime dependence in PADs was also observed. Plasma sheet PADs are isotropic or trapped. The plasma trough PADs are trapped or trapped and field aligned. Plasmaspheric electrons generally have energies too low to be detected.

Fillingim, M., M. Moldwin, H. Rassoul, P. Parrish, G. Birnbaum, M. Thomsen, and D. McComas, Low-energy electron PAD observations during plasmaspheric refilling, abstract SM72D-05, presented at the 1996 AGU Fall Meeting, San Francisco, CA, December 15 - 19, 2996.

Six months of electron plasma data collected using the magnetospheric plasma analyzer (MPA) instrument onboard the geosynchronous satellite 1989-046 have been surveyed. Electrons in the energy range 15-200 eV were characterized by local time of occurance, surrounding plasma environment, geomagnetic activity (Kp), and pitch-angle distribution (PAD). For this study special emphasis has been placed on the PADs of low-energy electrons observed during the plasmaspheric refilling process. Preliminary statistical results indicate a local time dependence in PADs, with trapped distributions primarily being observed in the early and late morning, coincident trapped and field-aligned PADs occurring around noon, and field-aligned PADs observed noon to midnight. When both field-aligned and trapped PADs exist, the field-aligned electrons generally have lower energies than the trapped electrons.

Branly, R. M., R. I. Athauda, M. O. Fillingim, and W. Van Hamme (1996), Light curve solutions for eclipsing binaries in NGC 188, Astrophysics and Space Science, 235(1), 149-160.

We present light curve solutions for the W UMa-type eclipsing binaries EP, EQ, ER, ES, and V369 Cep in the old open cluster NGC 188. Using light curve solution parameters combined with reasonable mass estimates, we determine the distance modulus V-M_V of the cluster. Our aim is to examine if current uncertainties in the cluster's distance and age can be resolved. Three binaries yield distance moduli close to 10.80^m (± 0.08^m), two others give values around 11.40^m (± 0.09^m). Depending on the amount of reddening, we find a weighted mean distance modulus for all five binaries between 11.01^m and 11.05^m (± 0.06^m), which lends modest support for the lower distance (1.65 kpc) and older age (10 Gyr) of the cluster.

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