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J D Huba - One of the best experts on this subject based on the ideXlab platform.
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erosion of the Plasmasphere during a storm
Journal of Geophysical Research, 2017Co-Authors: J Krall, J D Huba, S SazykinAbstract:The erosion of the Plasmasphere during a storm is analyzed using the Naval Research Laboratory (NRL) Sami3 is Also a Model of the Ionosphere (SAMI3) ionosphere/Plasmasphere code, coupled to the Rice Convection Model (RCM) of the inner magnetosphere and ring current. We reproduce the commonly-observed post-storm Plasmasphere profile, with strong erosion outside of a sharp, post-storm plasmapause and weak erosion inside the plasmapause. We find that inclusion of the ring current E field sharpens the post-storm plasmapause. In the case of a weak storm, erosion inside the post-storm plasmapause might not occur. In all cases, plasma flows are dominated by E × B drifts. For strong storms, we find that erosion, both inside and outside of the post-storm plasmapause, is caused by outward E × B drifts.
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the Plasmasphere electron content paradox
Journal of Geophysical Research, 2016Co-Authors: J Krall, J D HubaAbstract:Measurements show that Plasmasphere refilling rates decrease with increasing solar activity, while paradoxically, the vertical integration of the Plasmasphere electron density (pTEC) increases with increasing solar activity. Using the Naval Research Laboratory SAMI2 (Sami2 is Another Model of the Ionosphere) and SAMI3 (Sami3 is Also a Model of the Ionosphere) codes, we simulate Plasmasphere refilling following a model storm, reproducing this observed phenomenon. In doing so, we find that the refilling rate and resulting pTEC values are sensitive to the oxygen profile in the thermosphere and exosphere: the supply of H+ in the topside ionosphere is limited by the local O+ density, through H+O+→H++O charge exchange. At solar minimum, the O+ supply simply increases with the O density in the exosphere. At solar maximum, we find that O-O+ collisions limit the O+ density in the topside ionosphere such that it decreases with increasing O density. The paradox occurs because the pTEC metric gives electrons in the topside ionosphere more weight than electrons in the Plasmasphere.
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measurement and modeling of the refilling Plasmasphere during 2001
Journal of Geophysical Research, 2016Co-Authors: J Krall, J D Huba, V K Jordanova, R E Denton, T Carranza, M B MoldwinAbstract:The Naval Research Laboratory SAMI3 (Sami3 is Also a Model of the Ionosphere) and the RAM-CPL (Ring current Atmosphere interaction Model-Cold PLasma) codes are used to model observed Plasmasphere dynamics during 25 November 2001 to 1 December 2001 and 1–5 February 2001. Model results compare well to Plasmasphere observations of electron and mass densities. Comparison of model results to refilling data and to each other shows good agreement, generally within a factor of 2. We find that SAMI3 plasmaspheric refilling rates and ion densities are sensitive to the composition and temperature of the thermosphere and exosphere, and to photoelectron heating. Furthermore, results also support our previous finding that the wind-driven dynamo significantly impacts both refilling rates and Plasmasphere dynamics during quiet periods.
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the effect of the thermosphere on quiet time Plasmasphere morphology
Journal of Geophysical Research, 2014Co-Authors: J Krall, J D Huba, R E Denton, G Crowley, T W WuAbstract:The Naval Research Laboratory SAMI3 (Sami3 is Also a Model of the Ionosphere) code is used to model observed Plasmasphere dynamics for 1–5 February 2001, a period of quiet time refilling. The SAMI3 model is driven at high latitudes by the magnetospheric potential calculated by the Weimer05 empirical model, using the observed solar wind. At middle-to-low latitudes, the self-consistent dynamo potential is included, driven by specified winds. During this quiet period we find that the shape of the Plasmasphere, at any given time, varies significantly with the wind model even as a similar degree of model-data agreement is recovered for each of the three wind models used. Diurnal oscillations in the model electron density, which are strong when plotted at fixed magnetic local time, are consistent with the degree of variation seen in the measured densities. In all three cases, SAMI3 compares favorably to the electron density measured in situ by the Imager for Magnetopause-to-Aurora Global Exploration spacecraft. Results with no winds or with specific wind effects excluded show that wind-driven E × B drifts shape the Plasmasphere, relative to a round Plasmasphere with no winds, and reduce the refilling rate, relative to the higher refilling rate found without winds.
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sami3 simulation of Plasmasphere refilling
Geophysical Research Letters, 2013Co-Authors: J Krall, J D HubaAbstract:[1] The Naval Research Laboratory three-dimensional, first-principles simulation code SAMI3 (Sami3 is Also a Model of the Ionosphere) is used to model Plasmasphere refilling. A time-dependent Volland-Stern-Maynard-Chen potential is used to model an idealized magnetic storm that erodes the Plasmasphere to L<3. The potential is then relaxed to the prestorm state, and refilling is simulated for a range of L shells 3≤L≤5 over a period of 7 days. Refilling rates compare well to observed refilling rates. The model Plasmasphere during this quiet period displays a day-to-day repetition in its morphology that has not been previously observed.
W Li - One of the best experts on this subject based on the ideXlab platform.
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the trapping of equatorial magnetosonic waves in the earth s outer Plasmasphere
Geophysical Research Letters, 2014Co-Authors: W Li, R M Thorne, Lunjin Chen, G D Reeves, C A Kletzing, G B Hospodarsky, W S Kurth, M G Henderson, H E SpenceAbstract:We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth's Plasmasphere. Intense equatorial magnetosonic waves were observed inside the Plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner Plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth's Plasmasphere at locations away from the generation region.
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an unusual enhancement of low frequency plasmaspheric hiss in the outer Plasmasphere associated with substorm injected electrons
Geophysical Research Letters, 2013Co-Authors: W Li, William S. Kurth, R M Thorne, J Bortnik, G D Reeves, C A Kletzing, G B Hospodarsky, H E Spence, J B Blake, J F FennellAbstract:[1] Both plasmaspheric hiss and chorus waves were observed simultaneously by the two Van Allen Probes in association with substorm-injected energetic electrons. Probe A, located inside the Plasmasphere in the postdawn sector, observed intense plasmaspheric hiss, whereas Probe B observed chorus waves outside the Plasmasphere just before dawn. Dispersed injections of energetic electrons were observed in the dayside outer Plasmasphere associated with significant intensification of plasmaspheric hiss at frequencies down to ~20 Hz, much lower than typical hiss wave frequencies of 100–2000 Hz. In the outer Plasmasphere, the upper energy of injected electrons agrees well with the minimum cyclotron resonant energy calculated for the lower cutoff frequency of the observed hiss, and computed convective linear growth rates indicate instability at the observed low frequencies. This suggests that the unusual low-frequency plasmaspheric hiss is likely to be amplified in the outer Plasmasphere due to the injected energetic electrons.
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amplification of whistler mode hiss inside the Plasmasphere
Geophysical Research Letters, 2012Co-Authors: Lunjin Chen, W Li, J Bortnik, R M ThorneAbstract:[1] Chorus generated outside the Plasmasphere has been suggested to be the source of plasmaspheric hiss. A detailed evaluation of the propagation and Landau damping of chorus waves can account for most of the properties of dayside hiss, but the intensity is underestimated by 10–20 dB compared to the observed hiss intensity. We show that this important discrepancy is due to the neglect of cyclotron resonant growth inside the Plasmasphere. Careful modeling of the access of chorus to form an embryonic source outside the plasmapause, together with internal amplification inside the Plasmasphere can account for the spectral intensity of dayside plasmaspheric hiss.
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global distributions of suprathermal electrons observed on themis and potential mechanisms for access into the Plasmasphere
Journal of Geophysical Research, 2010Co-Authors: W Li, R M Thorne, J Bortnik, Y Nishimura, V Angelopoulos, Lunjin Chen, J P Mcfadden, J W BonnellAbstract:[1] Statistical results on the global distribution of suprathermal electron (0.1–10 keV) fluxes are shown both outside and inside the Plasmasphere separately, using electron data from THEMIS. Significant electron fluxes are found within the Plasmasphere, although they are nevertheless smaller than the populations outside the Plasmasphere. Electron fluxes outside of the plasmapause increase with stronger magnetic activity on the nightside and decrease as a function of increasing magnetic local time (MLT). Inside the Plasmasphere, electron fluxes increase just inside of the plasmapause, particularly from the midnight to the dawn sector during active times, while electron distributions are less MLT-dependent during quiet times. Inside the Plasmasphere, electron fluxes are larger and more stable at smaller L shells at higher energy (a few to 10 keV), while electron fluxes decrease at smaller L shells at lower energy (less than a few keV). Our new statistical results on the suprathermal electron distribution both inside and outside the Plasmasphere provide essential information for the evaluation of wave propagation characteristics. Case analyses have been performed in order to understand potential mechanisms responsible for electron access into the Plasmasphere. The first case analysis shows that during a relatively quiet time following a disturbed interval, deeply injected suprathermal electrons remain trapped at low L shells during the refilling of the Plasmasphere and eventually form the plasmaspheric population. The second case analysis suggests that a combination of locally enhanced electric field and subsequent energy-dependent azimuthal magnetic drift may be able to trap the suprathermal electrons inside the Plasmasphere during a geomagnetically active period.
R M Thorne - One of the best experts on this subject based on the ideXlab platform.
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the trapping of equatorial magnetosonic waves in the earth s outer Plasmasphere
Geophysical Research Letters, 2014Co-Authors: W Li, R M Thorne, Lunjin Chen, G D Reeves, C A Kletzing, G B Hospodarsky, W S Kurth, M G Henderson, H E SpenceAbstract:We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth's Plasmasphere. Intense equatorial magnetosonic waves were observed inside the Plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner Plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth's Plasmasphere at locations away from the generation region.
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an unusual enhancement of low frequency plasmaspheric hiss in the outer Plasmasphere associated with substorm injected electrons
Geophysical Research Letters, 2013Co-Authors: W Li, William S. Kurth, R M Thorne, J Bortnik, G D Reeves, C A Kletzing, G B Hospodarsky, H E Spence, J B Blake, J F FennellAbstract:[1] Both plasmaspheric hiss and chorus waves were observed simultaneously by the two Van Allen Probes in association with substorm-injected energetic electrons. Probe A, located inside the Plasmasphere in the postdawn sector, observed intense plasmaspheric hiss, whereas Probe B observed chorus waves outside the Plasmasphere just before dawn. Dispersed injections of energetic electrons were observed in the dayside outer Plasmasphere associated with significant intensification of plasmaspheric hiss at frequencies down to ~20 Hz, much lower than typical hiss wave frequencies of 100–2000 Hz. In the outer Plasmasphere, the upper energy of injected electrons agrees well with the minimum cyclotron resonant energy calculated for the lower cutoff frequency of the observed hiss, and computed convective linear growth rates indicate instability at the observed low frequencies. This suggests that the unusual low-frequency plasmaspheric hiss is likely to be amplified in the outer Plasmasphere due to the injected energetic electrons.
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amplification of whistler mode hiss inside the Plasmasphere
Geophysical Research Letters, 2012Co-Authors: Lunjin Chen, W Li, J Bortnik, R M ThorneAbstract:[1] Chorus generated outside the Plasmasphere has been suggested to be the source of plasmaspheric hiss. A detailed evaluation of the propagation and Landau damping of chorus waves can account for most of the properties of dayside hiss, but the intensity is underestimated by 10–20 dB compared to the observed hiss intensity. We show that this important discrepancy is due to the neglect of cyclotron resonant growth inside the Plasmasphere. Careful modeling of the access of chorus to form an embryonic source outside the plasmapause, together with internal amplification inside the Plasmasphere can account for the spectral intensity of dayside plasmaspheric hiss.
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global distributions of suprathermal electrons observed on themis and potential mechanisms for access into the Plasmasphere
Journal of Geophysical Research, 2010Co-Authors: W Li, R M Thorne, J Bortnik, Y Nishimura, V Angelopoulos, Lunjin Chen, J P Mcfadden, J W BonnellAbstract:[1] Statistical results on the global distribution of suprathermal electron (0.1–10 keV) fluxes are shown both outside and inside the Plasmasphere separately, using electron data from THEMIS. Significant electron fluxes are found within the Plasmasphere, although they are nevertheless smaller than the populations outside the Plasmasphere. Electron fluxes outside of the plasmapause increase with stronger magnetic activity on the nightside and decrease as a function of increasing magnetic local time (MLT). Inside the Plasmasphere, electron fluxes increase just inside of the plasmapause, particularly from the midnight to the dawn sector during active times, while electron distributions are less MLT-dependent during quiet times. Inside the Plasmasphere, electron fluxes are larger and more stable at smaller L shells at higher energy (a few to 10 keV), while electron fluxes decrease at smaller L shells at lower energy (less than a few keV). Our new statistical results on the suprathermal electron distribution both inside and outside the Plasmasphere provide essential information for the evaluation of wave propagation characteristics. Case analyses have been performed in order to understand potential mechanisms responsible for electron access into the Plasmasphere. The first case analysis shows that during a relatively quiet time following a disturbed interval, deeply injected suprathermal electrons remain trapped at low L shells during the refilling of the Plasmasphere and eventually form the plasmaspheric population. The second case analysis suggests that a combination of locally enhanced electric field and subsequent energy-dependent azimuthal magnetic drift may be able to trap the suprathermal electrons inside the Plasmasphere during a geomagnetically active period.
M B Moldwin - One of the best experts on this subject based on the ideXlab platform.
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measurement and modeling of the refilling Plasmasphere during 2001
Journal of Geophysical Research, 2016Co-Authors: J Krall, J D Huba, V K Jordanova, R E Denton, T Carranza, M B MoldwinAbstract:The Naval Research Laboratory SAMI3 (Sami3 is Also a Model of the Ionosphere) and the RAM-CPL (Ring current Atmosphere interaction Model-Cold PLasma) codes are used to model observed Plasmasphere dynamics during 25 November 2001 to 1 December 2001 and 1–5 February 2001. Model results compare well to Plasmasphere observations of electron and mass densities. Comparison of model results to refilling data and to each other shows good agreement, generally within a factor of 2. We find that SAMI3 plasmaspheric refilling rates and ion densities are sensitive to the composition and temperature of the thermosphere and exosphere, and to photoelectron heating. Furthermore, results also support our previous finding that the wind-driven dynamo significantly impacts both refilling rates and Plasmasphere dynamics during quiet periods.
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pc5 wave power in the quiet time Plasmasphere and trough crres observations
Geophysical Research Letters, 2010Co-Authors: M D Hartinger, Y Nishimura, V Angelopoulos, M B Moldwin, R R Anderson, K Takahashi, H J Singer, J R WygantAbstract:[1] The Combined Release and Radiation Effects Satellite (CRRES) mission provides an opportunity to study the distribution of MHD wave power in the inner magnetosphere both inside the high-density Plasmasphere and in the low-density trough. We present a statistical survey of Pc5 power using CRRES magnetic field, electric field, and plasma wave data separated into Plasmasphere and trough intervals. Using a database of plasmapause crossings, we examined differences in power spectral density between the Plasmasphere and trough regions. These differences were typically a factor of 3 or 4 but could be as much as an order of magnitude and could be seen in both electric and magnetic field data. Our study shows that determining the plasmapause location is important for understanding and modeling the MHD wave environment in the Pc5 frequency band.
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crres observations of density cavities inside the Plasmasphere
Journal of Geophysical Research, 2000Co-Authors: D L Carpenter, R R Anderson, W Calvert, M B MoldwinAbstract:Deep density troughs inside the Plasmasphere in which electron density was a factor of from ∼2 to 10 below nearby Plasmasphere levels were found in ∼13% of 1764 near-equatorial electron density profiles derived from the sweep frequency receiver data acquired in 1990–1991 by the CRRES satellite. These “inner troughs” appeared in the aftermath of Plasmasphere erosion episodes and are interpreted as the near-equatorial manifestations of geomagnetic-field-aligned cavities. Inner troughs were found at all local times but were most common in the 1800–2400 magnetic local time (MLT) sector and least common between 0600 and 1200 MLT. Their inner boundaries, plasmapause-like in form, were mostly at L < 3.5 but in ∼30% of the cases were at L < 2.5 under geomagnetic conditions that traditionally have been associated with plasmapause radii in the L = 3–3.5 range or beyond. The trough outer walls were exceptionally steep, in several cases exhibiting a factor of 4 or more density change within less than 100 km along the near-equatorial satellite orbit. The extent of the troughs in L ranged from ΔL ∼ 0.5 to 2, and various forms of evidence, including earlier studies, suggest an extent of more than 20° in longitude. Such evidence includes plasma waves propagating in a free space mode within the inner trough while extending in frequency well above the upper limit of trapped continuum radiation detected beyond the Plasmasphere. We suggest, as have previous authors, that the troughs are translated vestiges of plasma configurations established during preceding periods of Plasmasphere erosion. In some such cases, dense plasma features lying beyond the troughs were probably connected to the main Plasmasphere in a local time sector to the east of the observing longitude. However, in some of the cases of troughs with steep outer walls the dense plasma feature beyond that wall may have been shaped by a mechanism for detaching plasma from an originally larger outer Plasmasphere, such as by shear flows in the premidnight sector associated with subauroral ion drifts.
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an examination of the structure and dynamics of the outer Plasmasphere using multiple geosynchronous satellites
Journal of Geophysical Research, 1994Co-Authors: M B Moldwin, M F Thomsen, S J Bame, D J Mccomas, K R MooreAbstract: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.
H E Spence - One of the best experts on this subject based on the ideXlab platform.
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penetration of magnetosonic waves into the Plasmasphere observed by the van allen probes
Geophysical Research Letters, 2015Co-Authors: Fuliang Xiao, G D Reeves, H E Spence, Qinghua Zhou, Yihua He, Chang Yang, D N Baker, Herbert O Funsten, J B BlakeAbstract:During the small storm on 14–15 April 2014, Van Allen Probe A measured a continuously distinct proton ring distribution and enhanced magnetosonic (MS) waves along its orbit outside the plasmapause. Inside the Plasmasphere, strong MS waves were still present but the distinct proton ring distribution was falling steeply with distance. We adopt a sum of subtracted bi-Maxwellian components to model the observed proton ring distribution and simulate the wave trajectory and growth. MS waves at first propagate toward lower L shells outside the Plasmasphere, with rapidly increasing path gains related to the continuous proton ring distribution. The waves then gradually cross the plasmapause into the deep Plasmasphere, with almost unchanged path gains due to the falling proton ring distribution and higher ambient density. These results present the first report on how MS waves penetrate into the Plasmasphere with the aid of the continuous proton ring distributions during weak geomagnetic activities.
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the trapping of equatorial magnetosonic waves in the earth s outer Plasmasphere
Geophysical Research Letters, 2014Co-Authors: W Li, R M Thorne, Lunjin Chen, G D Reeves, C A Kletzing, G B Hospodarsky, W S Kurth, M G Henderson, H E SpenceAbstract:We investigate the excitation and propagation of equatorial magnetosonic waves observed by the Van Allen Probes and describe evidence for a trapping mechanism for magnetosonic waves in the Earth's Plasmasphere. Intense equatorial magnetosonic waves were observed inside the Plasmasphere in association with a pronounced proton ring distribution, which provides free energy for wave excitation. Instability analysis along the inbound orbit demonstrates that broadband magnetosonic waves can be excited over a localized spatial region near the plasmapause. The waves can subsequently propagate into the inner Plasmasphere and remain trapped over a limited radial extent, consistent with the predictions of near-perpendicular propagation. By performing a similar analysis on another observed magnetosonic wave event, we demonstrate that magnetosonic waves can also be trapped within local density structures. We suggest that perpendicular wave propagation is important for explaining the presence of magnetosonic waves in the Earth's Plasmasphere at locations away from the generation region.
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an unusual enhancement of low frequency plasmaspheric hiss in the outer Plasmasphere associated with substorm injected electrons
Geophysical Research Letters, 2013Co-Authors: W Li, William S. Kurth, R M Thorne, J Bortnik, G D Reeves, C A Kletzing, G B Hospodarsky, H E Spence, J B Blake, J F FennellAbstract:[1] Both plasmaspheric hiss and chorus waves were observed simultaneously by the two Van Allen Probes in association with substorm-injected energetic electrons. Probe A, located inside the Plasmasphere in the postdawn sector, observed intense plasmaspheric hiss, whereas Probe B observed chorus waves outside the Plasmasphere just before dawn. Dispersed injections of energetic electrons were observed in the dayside outer Plasmasphere associated with significant intensification of plasmaspheric hiss at frequencies down to ~20 Hz, much lower than typical hiss wave frequencies of 100–2000 Hz. In the outer Plasmasphere, the upper energy of injected electrons agrees well with the minimum cyclotron resonant energy calculated for the lower cutoff frequency of the observed hiss, and computed convective linear growth rates indicate instability at the observed low frequencies. This suggests that the unusual low-frequency plasmaspheric hiss is likely to be amplified in the outer Plasmasphere due to the injected energetic electrons.
