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T E Cayton - One of the best experts on this subject based on the ideXlab platform.

  • entropy mapping of the outer electron radiation belt between the magnetotail and Geosynchronous orbit
    Journal of Geophysical Research, 2011
    Co-Authors: Joseph E Borovsky, T E Cayton
    Abstract:

    [1] The specific entropy (entropy density) S is examined for the outer electron radiation belt at Geosynchronous orbit and for the energetic electron population in the Earth's magnetotail. The outer electron radiation belt is measured with the SOPA detectors on board six Geosynchronous Satellites and the energetic electrons of the magnetotail are measured with instrumentation on board 12 Global Positioning Satellites (GPS) with a magnetic field model used to map the GPS orbit to the magnetotail. Density n and temperature T values are determined from relativistic Maxwellian fits to the electron measurements, enabling the specific entropy S to be calculated. For low temperatures the nonrelativstic specific entropy is S = T/n2/3; for a relativistic Maxwellian distribution a relativistically correct expression for S = S(T,n) is derived and used. The outer electron radiation belt at Geosynchronous orbit local midnight (n ∼ 3 × 10−4 cm−3 and T ∼ 140 keV) and the energetic-electron population in the magnetotail (n ∼ 1 × 10−4 cm−3 and T ∼ 50 keV) statistically have the same specific entropy. Hence the two populations are probably the same. This implies adiabatic transport (1) from the magnetotail to the dipole (where the magnetotail electrons are the source of the outer electron radiation belt) or (2) from the dipole to the magnetotail (where the magnetotail electrons are leakage from the radiation belt).

  • effects of a high density plasma sheet on ring current development during the november 2 6 1993 magnetic storm
    Journal of Geophysical Research, 1998
    Co-Authors: J U Kozyra, M F Thomsen, V K Jordanova, J E Borovsky, Delores J Knipp, D S Evans, D J Mccomas, T E Cayton
    Abstract:

    The growth and recovery of the November 2–6, 1993 magnetic storm was simulated using a drift-loss ring current model that was driven by dynamic fluxes at Geosynchronous orbit as an outer boundary condition. During the storm main phase, a high-density plasma sheet was observed by the Los Alamos National Laboratory Geosynchronous Satellites to move into and flow around the inner magnetosphere over a period of ∼12 hours [Borovsky et al., 1997; this issue] during the storm main phase. Densities at the leading edge of this structure reached 3 cm−3 as compared with more typical values <1 cm−3. The factor of 3 change in the plasma sheet density from quiet to active times produced a factor of 3 enhancement in the strength of the simulated ring current. In addition, a short-timescale recovery in the Dst index at 1600 UT on November 4 was driven by changes in the outer boundary condition and appeared even in the absence of collisional losses. An overshoot in the minimum Dst* occurred in the simulated ring current compared with observed values at ∼0200 UT on November 4 and is taken as evidence of a loss process not included in the ring current-atmosphere interaction model (RAM). The storm onset was associated with a compression of the entire dayside magnetopause to within geostationary orbit starting at 2307 UT and continuing for a half hour. It is suggested that a possible additional loss may have resulted as ions drifted to the compressed dayside magnetopause. In fact such losses were found in another simulation of the inner magnetosphere for the same storm by Freeman et al. [1996]. The energy supplied to the inner magnetosphere, relative to the total energy input during this magnetic storm, was examined by comparing two widely used energy input functions, the e parameter [Akasofu, 1981] and the F parameter [Burton et al., 1975] against energy input to the ring current model based on Geosynchronous plasma observations at the outer boundary. It is found that the e parameter [Akasofu, 1981] overestimates the ring current energy input compared to the drift-loss model by almost an order of magnitude during the main phase. However, the integrated energy input from e, over the 4 day interval of the storm, is in very good agreement with the total energy input inferred from observations. On the other hand, F more closely approximates the magnitude of the ring current energy input alone as calculated in the drift-loss model. An energy budget is constructed for the storm that shows energy inputs from the solar wind and energy dissipation due to ring current buildup and decay, auroral electron precipitation, Joule heating, ion precipitation, and energy storage in the magnetotail in reasonable balance. The ring current energy input accounts for only 15% of the total dissipated energy in this storm interval. A more complete energy budget that extends to November 11, 1993, was compiled by Knipp et al. [this issue].

  • multisatellite observations of the outer zone electron variation during the november 3 4 1993 magnetic storm
    Journal of Geophysical Research, 1997
    Co-Authors: D N Baker, M Temerin, T E Cayton, E G D Reeves, R A Christensen, J B Blake, M D Looper, R Nakamura, S G Kanekal
    Abstract:

    The disappearance and reappearance of outer zone energetic electrons during the November 3{endash}4, 1993, magnetic storm is examined utilizing data from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), the Global Positioning System (GPS) series, and the Los Alamos National Laboratory (LANL) sensors onboard Geosynchronous Satellites. The relativistic electron flux drops during the main phase of the magnetic storm in association with the large negative interplanetary B{sub z} and rapid solar wind pressure increase late on November 3. Outer zone electrons with E{gt}3MeV measured by SAMPEX disappear for over 12 hours at the beginning of November 4. This represents a 3 orders of magnitude decrease down to the cosmic ray background of the detector. GPS and LANL sensors show similar effects, confirming that the flux drop of the energetic electrons occurs near the magnetic equator and at all pitch angles. Enhanced electron precipitation was measured by SAMPEX at L{ge}3.5. The outer zone electron fluxes then recover and exceed prestorm levels within one day of the storm onset and the inner boundary of the outer zone moves inward to smaller L ({lt}3). These measurements provide a data set which is examined in detail and used to determine the mechanisms contributing tomore » the loss and recovery of the outer zone electron flux. The loss of the inner part of the outer zone electrons is partly due to the adiabatic effects associated with the decrease of Dst, while the loss of most of the outer part (those electrons initially at L{ge}4.0) is due to either precipitation into the atmosphere or drift to the magnetopause because of the strong compression of the magnetosphere by the solar wind. The recovery of the energetic electron flux is due to the adiabatic effects associated with the increase in Dst, and at lower energies ({lt}0.5MeV) due to rapid radial diffusion driven by the strong magnetic activity during the recovery phase of the storm. (Abstract Truncated)« less

G D Reeves - One of the best experts on this subject based on the ideXlab platform.

  • comparisons between ion distributions retrieved from ena images of the ring current and contemporaneous multipoint ion measurements recorded in situ during the major magnetic storm of 15 may 2005
    Journal of Geophysical Research, 2010
    Co-Authors: S Mckennalawlor, S Barabash, P C Brandt, J Balaz, Z Liu, G D Reeves
    Abstract:

    [1] The Neutral Atom Detector Unit (NUADU) aboard the TC-2 spacecraft recorded energetic neutral atom (ENA) image data for >3 h during part of the main and recovery phases of a major magnetic storm on 15 May 2005. A custom designed, constrained linear inversion method was applied to retrieve ring current ion distributions in the ENA records out to L = 6.6. Comparisons were then made between the ion fluxes retrieved from these ENA data (energy ranges 50–81 keV and 81–158 keV) and complementary, contemporaneous particle fluxes measured in situ by Synchronous Orbit Particle Analyzer (SOPA) instruments aboard a series of Geosynchronous Satellites that were launched to encircle the equatorial plane at L ∼ 6.6 by the Los Alamos National Laboratory (LANL). The ENA data revealed the development of two emission peaks during the main phase of the storm which corresponded to the arrival from the magnetotail of a pair of particle injections. These injections reached, in each case, maximum value before the corresponding AL index amplitude peak was attained. The main phase of the storm concluded (Dst ≈ −256 nT) in the aftermath of this event pair, and the ring current ion fluxes thereafter gradually decayed over several hours (the storm recovery phase). This is the first time that the linear inversion method developed for NUADU data has been globally validated using multipoint in situ measurements made at different magnetic local times. It was found that the higher the derived flux values were on the duskside/nightside, the closer they were to the in situ measurements. The retrieved fluxes obtained on the duskside/nightside tended, however, to be still somewhat underestimated since the ENA measurements concerned were made around the outer edge of the ring current at an altitude where the magnetic field in the inner magnetosphere deviates from that dipole configuration assumed in the inversion procedure to pertain there. The two methods utilized to study ions during a large magnetic storm are complementary in that the retrieved ion fluxes provide high time resolution information concerning the changing, large-scale structure of ring current events, whereas in situ flux sampling presents “measurement truth” at particular locations within individual ring currents.

  • phase space density distributions of energetic electrons in the outer radiation belt during two geospace environment modeling inner magnetosphere storms selected storms
    Journal of Geophysical Research, 2006
    Co-Authors: Yue Chen, R H W Friedel, G D Reeves
    Abstract:

    [1] The phase space density distributions of energetic electrons during two storm periods, including the two storms on 21–23 October 2001 and 4–9 September 2002 selected by Geospace Environment Modeling Inner Magnetosphere/Storms campaign as the radiation belt assessment challenge in 2004 workshop, are presented in this paper. Electron data from the Synchronous Orbit Particle Analysis instrument aboard three Los Alamos National Laboratory Geosynchronous Satellites as well as the Comprehensive Energetic Particle and Pitch Angle Distribution instrument aboard Polar are used. The Tsyganenko 2001 storm model is chosen for the storm time magnetic field presentation, compared to the best-fitting magnetic model achieved in a previous study. By tracing the temporally evolving radial distributions, we conclude that while the dropout of electron phase space density during storm main phases appears to be energy-independent, the enhancement in recovery phases shows an energy-dependent pattern. The average outwardly decreasing radial gradients of phase space density obtained during the recovery phases of the two storm periods strongly suggest the in situ acceleration is most likely the main source of new energetic electrons, along with a possible contribution from an external source.

  • are sawtooth oscillations of energetic plasma particle fluxes caused by periodic substorms or driven by solar wind pressure enhancements
    Journal of Geophysical Research, 2005
    Co-Authors: Chao Song Huang, G D Reeves, Kiyo Yumoto
    Abstract:

    [1] Energetic electron and proton fluxes measured by Geosynchronous Satellites often show sawtooth-like variations during magnetic storms. We examine whether the sawtooth oscillations and relevant magnetospheric-ionospheric disturbances are caused by periodic substorms or driven by a series of enhancements in the solar wind pressure. We show that there are significant differences between periodic substorms and solar wind-induced variations. The energetic fluxes at Geosynchronous orbit may increase by orders of magnitude after each onset of periodic substorms and by 10–50% in response to a large solar wind pressure impulse. The sudden increases of the energetic fluxes during periodic substorms show significant time delays of 30–50 min at different longitudes/local times, indicating that the fluxes are injected on the nightside and then drift to the dayside. In contrast, the small flux increases caused by solar wind pressure enhancements occur almost simultaneously at all local times. The periodic substorms always have a strong spectrum peak at 2–3 hours, no matter whether the solar wind pressure and/or IMF have similar spectrum peaks. The nightside magnetospheric magnetic elevation angle shows a large (30–60°) increase at each onset of periodic substorms through dipolarization and a small (<10°) decrease in response to a solar wind pressure impulse. Each cycle of periodic substorms can cause a deviation of 40–60 nT in the midlatitude geomagnetic field; the midlatitude geomagnetic deviations caused by solar wind pressure enhancements are proportional to the square root of the pressure change. The increase of the polar cap index caused by substorms is ∼4 times that caused by solar wind pressure enhancements. We conclude that the sawtooth-like flux oscillations represent flux injections during periodic substorms and that the period of substorms is determined by the magnetosphere.

  • the relativistic electron response at Geosynchronous orbit during the january 1997 magnetic storm
    Journal of Geophysical Research, 1998
    Co-Authors: G D Reeves, H J Singer, R H W Friedel, D N Baker, R D Belian, M M Meier, M G Henderson, T G Onsager, J B Blake
    Abstract:

    The first geomagnetic storm of 1997 began on January 10. It is of particular interest because it was exceptionally well observed by the full complement of International Solar Terrestrial Physics (ISTP) Satellites and because of its possible association with the catastrophic failure of the Telstar 401 telecommunications satellite. Here we report on the energetic electron environment observed by five Geosynchronous Satellites. In part one of this paper we examine the magnetospheric response to the magnetic cloud. The interval of southward IMF drove strong substorm activity while the interval of northward IMF and high solar wind density strongly compressed the magnetosphere. At energies above a few hundred keV, two distinct electron enhancements were observed at Geosynchronous orbit. The first enhancement began and ended suddenly, lasted for approximately 1 day, and is associated with the strong compression of the magnetosphere. The second enhancement showed a more characteristic time delay, peaking on January 15. Both enhancements may be due to transport of electrons from the same initial acceleration event at a location inside Geosynchronous orbit but the first enhancement was due to a temporary, quasi-adiabatic transport associated with the compression of the magnetosphere while the second enhancement was due to slower diffusive processes. In the second part of the paper we compare the relativistic electron fluxes measured simultaneously at different local times. We find that the >2-MeV electron fluxes increased first at noon followed by dusk and then dawn and that there can be difference of two orders of magnitude in the fluxes observed at different local times. Finally, we discuss the development of data-driven models of the relativistic electron belts for space weather applications. By interpolating fluxes between Satellites we produced a model that gives the >2-MeV electron fluxes at all local times as a function of universal time. In a first application of this model we show that, at least in this case, magnetopause shadowing does not contribute noticeably to relativistic electron dropouts.

Joseph E Borovsky - One of the best experts on this subject based on the ideXlab platform.

  • entropy mapping of the outer electron radiation belt between the magnetotail and Geosynchronous orbit
    Journal of Geophysical Research, 2011
    Co-Authors: Joseph E Borovsky, T E Cayton
    Abstract:

    [1] The specific entropy (entropy density) S is examined for the outer electron radiation belt at Geosynchronous orbit and for the energetic electron population in the Earth's magnetotail. The outer electron radiation belt is measured with the SOPA detectors on board six Geosynchronous Satellites and the energetic electrons of the magnetotail are measured with instrumentation on board 12 Global Positioning Satellites (GPS) with a magnetic field model used to map the GPS orbit to the magnetotail. Density n and temperature T values are determined from relativistic Maxwellian fits to the electron measurements, enabling the specific entropy S to be calculated. For low temperatures the nonrelativstic specific entropy is S = T/n2/3; for a relativistic Maxwellian distribution a relativistically correct expression for S = S(T,n) is derived and used. The outer electron radiation belt at Geosynchronous orbit local midnight (n ∼ 3 × 10−4 cm−3 and T ∼ 140 keV) and the energetic-electron population in the magnetotail (n ∼ 1 × 10−4 cm−3 and T ∼ 50 keV) statistically have the same specific entropy. Hence the two populations are probably the same. This implies adiabatic transport (1) from the magnetotail to the dipole (where the magnetotail electrons are the source of the outer electron radiation belt) or (2) from the dipole to the magnetotail (where the magnetotail electrons are leakage from the radiation belt).

M F Thomsen - One of the best experts on this subject based on the ideXlab platform.

  • statistics of plasma fluxes at Geosynchronous orbit over more than a full solar cycle
    Social Work, 2007
    Co-Authors: M F Thomsen, M H Denton, B Lavraud, M Bodeau
    Abstract:

    [1] The extensive database of plasma measurements from Los Alamos Geosynchronous Satellites is used to derive a statistical characterization of the Geosynchronous fluxes of ions and electrons between the energies of ∼40 eV and ∼45 keV. The database covers more than an entire solar cycle and all levels of geomagnetic activity. The derived flux averages and various percentile levels thus describe the environment to which Geosynchronous Satellites are exposed over their lifetimes and should provide a useful tool to guide satellite design and testing. The mission-averaged fluxes agree very well with other recent analyses in the energy ranges of overlap.

  • medium energy pitch angle distribution during substorm injected electron clouds
    Geophysical Research Letters, 2005
    Co-Authors: A Asnes, R W H Friedel, J Stadsnes, N Ostgaard, M F Thomsen
    Abstract:

    [1] An investigation of pitch angle resolved electron data of energy <47 keV made by the MPA instrument on LANL Geosynchronous Satellites reveals a signature of symmetric peaks in the pitch angle distributions, observed to expand from being nearly at perpendicular pitch angles (∼90°) to nearly field aligned at lower energies. This feature is seen in almost every interval of increased fluxes at Geosynchronous orbit. A closer examination reveals the expansion of the peak in pitch angle to be such that the corresponding parallel velocity (along B) is constant. In some time intervals there are simultaneous symmetric peaks in more than one energy band and the parallel energy corresponding to the symmetric peaks is seen to vary as function of time. The observations might be explained by particles interacting with whistler mode chorus through Landau resonance, diffusing particles with parallel velocity near the phase velocity of the waves.

  • effects of a high density plasma sheet on ring current development during the november 2 6 1993 magnetic storm
    Journal of Geophysical Research, 1998
    Co-Authors: J U Kozyra, M F Thomsen, V K Jordanova, J E Borovsky, Delores J Knipp, D S Evans, D J Mccomas, T E Cayton
    Abstract:

    The growth and recovery of the November 2–6, 1993 magnetic storm was simulated using a drift-loss ring current model that was driven by dynamic fluxes at Geosynchronous orbit as an outer boundary condition. During the storm main phase, a high-density plasma sheet was observed by the Los Alamos National Laboratory Geosynchronous Satellites to move into and flow around the inner magnetosphere over a period of ∼12 hours [Borovsky et al., 1997; this issue] during the storm main phase. Densities at the leading edge of this structure reached 3 cm−3 as compared with more typical values <1 cm−3. The factor of 3 change in the plasma sheet density from quiet to active times produced a factor of 3 enhancement in the strength of the simulated ring current. In addition, a short-timescale recovery in the Dst index at 1600 UT on November 4 was driven by changes in the outer boundary condition and appeared even in the absence of collisional losses. An overshoot in the minimum Dst* occurred in the simulated ring current compared with observed values at ∼0200 UT on November 4 and is taken as evidence of a loss process not included in the ring current-atmosphere interaction model (RAM). The storm onset was associated with a compression of the entire dayside magnetopause to within geostationary orbit starting at 2307 UT and continuing for a half hour. It is suggested that a possible additional loss may have resulted as ions drifted to the compressed dayside magnetopause. In fact such losses were found in another simulation of the inner magnetosphere for the same storm by Freeman et al. [1996]. The energy supplied to the inner magnetosphere, relative to the total energy input during this magnetic storm, was examined by comparing two widely used energy input functions, the e parameter [Akasofu, 1981] and the F parameter [Burton et al., 1975] against energy input to the ring current model based on Geosynchronous plasma observations at the outer boundary. It is found that the e parameter [Akasofu, 1981] overestimates the ring current energy input compared to the drift-loss model by almost an order of magnitude during the main phase. However, the integrated energy input from e, over the 4 day interval of the storm, is in very good agreement with the total energy input inferred from observations. On the other hand, F more closely approximates the magnitude of the ring current energy input alone as calculated in the drift-loss model. An energy budget is constructed for the storm that shows energy inputs from the solar wind and energy dissipation due to ring current buildup and decay, auroral electron precipitation, Joule heating, ion precipitation, and energy storage in the magnetotail in reasonable balance. The ring current energy input accounts for only 15% of the total dissipated energy in this storm interval. A more complete energy budget that extends to November 11, 1993, was compiled by Knipp et al. [this issue].

  • an examination of the structure and dynamics of the outer plasmasphere using multiple Geosynchronous Satellites
    Journal of Geophysical Research, 1994
    Co-Authors: Mark B. Moldwin, M F Thomsen, David J. Mccomas, S J Bame, K R Moore
    Abstract:

    The structure and the dynamics of the plasmaspheric bulge are examined using in situ three-dimensional plasma observations from magnetospheric plasma analyzers onboard multiple Geosynchronous Satellites. We identify the plasmasphere by the presence of high fluxes of low-energy (≈ few eV) ions (corresponding to densities of ≈10s up to ≈100 cm−3). The results from one year (1991) of nearly continuous plasma measurements from two longitudinally and latitudinally separated spacecraft are presented. This study corroborates many of the features and statistical behavior of the plasmaspheric bulge evidenced in past ground-based and single spacecraft data sets, except we often find a more complex outer plasmasphere than earlier studies have suggested. By using multipoint, simultaneous observations to separate spatial from temporal changes, this study extends previous examinations of the plasmasphere at synchronous orbit. We find that the width and location of the plasmaspheric bulge can differ significantly for the two spacecraft (separated by 6-8 hours in time), particularly during quiet geomagnetic conditions. The very different plasmaspheric morphologies seen by the two spacecraft lead us to conclude that the outer plasmasphere is often highly structured even during steady geomagnetic conditions and that the simple teardrop model of the bulge rarely, if ever, adequately describes the duskside plasmasphere.

J B Blake - One of the best experts on this subject based on the ideXlab platform.

  • the relativistic electron response at Geosynchronous orbit during the january 1997 magnetic storm
    Journal of Geophysical Research, 1998
    Co-Authors: G D Reeves, H J Singer, R H W Friedel, D N Baker, R D Belian, M M Meier, M G Henderson, T G Onsager, J B Blake
    Abstract:

    The first geomagnetic storm of 1997 began on January 10. It is of particular interest because it was exceptionally well observed by the full complement of International Solar Terrestrial Physics (ISTP) Satellites and because of its possible association with the catastrophic failure of the Telstar 401 telecommunications satellite. Here we report on the energetic electron environment observed by five Geosynchronous Satellites. In part one of this paper we examine the magnetospheric response to the magnetic cloud. The interval of southward IMF drove strong substorm activity while the interval of northward IMF and high solar wind density strongly compressed the magnetosphere. At energies above a few hundred keV, two distinct electron enhancements were observed at Geosynchronous orbit. The first enhancement began and ended suddenly, lasted for approximately 1 day, and is associated with the strong compression of the magnetosphere. The second enhancement showed a more characteristic time delay, peaking on January 15. Both enhancements may be due to transport of electrons from the same initial acceleration event at a location inside Geosynchronous orbit but the first enhancement was due to a temporary, quasi-adiabatic transport associated with the compression of the magnetosphere while the second enhancement was due to slower diffusive processes. In the second part of the paper we compare the relativistic electron fluxes measured simultaneously at different local times. We find that the >2-MeV electron fluxes increased first at noon followed by dusk and then dawn and that there can be difference of two orders of magnitude in the fluxes observed at different local times. Finally, we discuss the development of data-driven models of the relativistic electron belts for space weather applications. By interpolating fluxes between Satellites we produced a model that gives the >2-MeV electron fluxes at all local times as a function of universal time. In a first application of this model we show that, at least in this case, magnetopause shadowing does not contribute noticeably to relativistic electron dropouts.

  • multisatellite observations of the outer zone electron variation during the november 3 4 1993 magnetic storm
    Journal of Geophysical Research, 1997
    Co-Authors: D N Baker, M Temerin, T E Cayton, E G D Reeves, R A Christensen, J B Blake, M D Looper, R Nakamura, S G Kanekal
    Abstract:

    The disappearance and reappearance of outer zone energetic electrons during the November 3{endash}4, 1993, magnetic storm is examined utilizing data from the Solar, Anomalous, and Magnetospheric Particle Explorer (SAMPEX), the Global Positioning System (GPS) series, and the Los Alamos National Laboratory (LANL) sensors onboard Geosynchronous Satellites. The relativistic electron flux drops during the main phase of the magnetic storm in association with the large negative interplanetary B{sub z} and rapid solar wind pressure increase late on November 3. Outer zone electrons with E{gt}3MeV measured by SAMPEX disappear for over 12 hours at the beginning of November 4. This represents a 3 orders of magnitude decrease down to the cosmic ray background of the detector. GPS and LANL sensors show similar effects, confirming that the flux drop of the energetic electrons occurs near the magnetic equator and at all pitch angles. Enhanced electron precipitation was measured by SAMPEX at L{ge}3.5. The outer zone electron fluxes then recover and exceed prestorm levels within one day of the storm onset and the inner boundary of the outer zone moves inward to smaller L ({lt}3). These measurements provide a data set which is examined in detail and used to determine the mechanisms contributing tomore » the loss and recovery of the outer zone electron flux. The loss of the inner part of the outer zone electrons is partly due to the adiabatic effects associated with the decrease of Dst, while the loss of most of the outer part (those electrons initially at L{ge}4.0) is due to either precipitation into the atmosphere or drift to the magnetopause because of the strong compression of the magnetosphere by the solar wind. The recovery of the energetic electron flux is due to the adiabatic effects associated with the increase in Dst, and at lower energies ({lt}0.5MeV) due to rapid radial diffusion driven by the strong magnetic activity during the recovery phase of the storm. (Abstract Truncated)« less