Electron flux enhancement in the inner radiation belt during moderate magnetic storms

Abstract. During moderate magnetic storms, an electron channel (300–1100 keV) of the NOAA satellite has shown sudden electron flux enhancements in the inner radiation belt. After examinating the possibility of contamination by different energetic particles, we conclude that these electron flux enhancements are reliable enough to be considered as natural phenomena, at least for the cases of small to moderate magnetic storms. Here, we define small and moderate storms to be those in which the minimum Dst ranges between −30 and −100 nT. The electron flux enhancements appear with over one order of magnitude at L~2 during these storms. The enhancement is not accompanied by any transport of electron flux from the outer belt. Statistical analysis shows that these phenomena have a duration of approximately 1 day during the period, starting with the main phase to the early recovery phase of the storms. The flux enhancement shows a dawn-dusk asymmetry; the amount of increased flux is larger in the dusk side. We suggest that this phenomenon could not be caused by the radial diffusion but would be due to pitch-angle scattering at the magnetic equator. The inner belt is not in a stationary state, as was previously believed, but is variable in response to the magnetic activity.

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Multi-satellite simultaneous observations of magnetopause and atmospheric losses of radiation belt electrons during an intense solar wind dynamic pressure pulse

Annales Geophysicae ◽

10.5194/angeo-34-493-2016 ◽

2016 ◽

Vol 34 (5) ◽

pp. 493-509 ◽

Cited By ~ 15

Author(s):

Zheng Xiang ◽

Binbin Ni ◽

Chen Zhou ◽

Zhengyang Zou ◽

Xudong Gu ◽

...

Keyword(s):

Solar Wind ◽

Radiation Belt ◽

Pressure Pulse ◽

Electron Flux ◽

Dynamic Pressure ◽

Energetic Electron ◽

Solar Wind Dynamic Pressure ◽

Angle Scattering ◽

Radiation Belt Electrons ◽

Atmospheric Loss

Abstract. Radiation belt electron flux dropouts are a kind of drastic variation in the Earth's magnetosphere, understanding of which is of both scientific and societal importance. Using electron flux data from a group of 14 satellites, we report multi-satellite simultaneous observations of magnetopause and atmospheric losses of radiation belt electrons during an event of intense solar wind dynamic pressure pulse. When the pulse occurred, magnetopause and atmospheric loss could take effect concurrently contributing to the electron flux dropout. Losses through the magnetopause were observed to be efficient and significant at L ≳ 5, owing to the magnetopause intrusion into L ∼ 6 and outward radial diffusion associated with sharp negative gradient in electron phase space density. Losses to the atmosphere were directly identified from the precipitating electron flux observations, for which pitch angle scattering by plasma waves could be mainly responsible. While the convection and substorm injections strongly enhanced the energetic electron fluxes up to hundreds of keV, they could delay other than avoid the occurrence of electron flux dropout at these energies. It is demonstrated that the pulse-time radiation belt electron flux dropout depends strongly on the specific interplanetary and magnetospheric conditions and that losses through the magnetopause and to the atmosphere and enhancements of substorm injection play an essential role in combination, which should be incorporated as a whole into future simulations for comprehending the nature of radiation belt electron flux dropouts.

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The relativistic electron response in the outer radiation belt during magnetic storms

Annales Geophysicae ◽

10.5194/angeo-20-957-2002 ◽

2002 ◽

Vol 20 (7) ◽

pp. 957-965 ◽

Cited By ~ 55

Author(s):

R. H. A. Iles ◽

A. N. Fazakerley ◽

A. D. Johnstone ◽

N. P. Meredith ◽

P. Bühler

Keyword(s):

Magnetic Field ◽

Solar Wind ◽

Wind Speed ◽

Interplanetary Magnetic Field ◽

Relativistic Electron ◽

Radiation Belt ◽

Solar Wind Speed ◽

Recovery Phase ◽

Magnetic Storms ◽

Outer Radiation Belt

Abstract. The relativistic electron response in the outer radiation belt during magnetic storms has been studied in relation to solar wind and geomagnetic parameters during the first six months of 1995, a period in which there were a number of recurrent fast solar wind streams. The relativistic electron population was measured by instruments on board the two microsatellites, STRV-1a and STRV-1b, which traversed the radiation belt four times per day from L ~ 1 out to L ~ 7 on highly elliptical, near-equatorial orbits. Variations in the E > 750 keV and E > 1 MeV electrons during the main phase and recovery phase of 17 magnetic storms have been compared with the solar wind speed, interplanetary magnetic field z-component, Bz , the solar wind dynamic pressure and Dst *. Three different types of electron responses are identified, with outcomes that strongly depend on the solar wind speed and interplanetary magnetic field orientation during the magnetic storm recovery phase. Observations also confirm that the L-shell, at which the peak enhancement in the electron count rate occurs has a dependence on Dst *.Key words. Magnetospheric physics (energetic particles, trapped; storms and substorms) – Space plasma physics (charged particle motion and accelerations)

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The dynamics of the inner boundary of the outer radiation belt during geomagnetic storms

10.5194/egusphere-egu2020-19607 ◽

2020 ◽

Author(s):

Xiaofei Shi ◽

Jie Ren ◽

Qiugang Zong

Keyword(s):

Radiation Belt ◽

Electron Flux ◽

Geomagnetic Storms ◽

Minimum Energy ◽

Onset Time ◽

Recovery Phase ◽

Outer Radiation Belt ◽

H Index ◽

Late Recovery ◽

Energy Dependent

We present a statistical study of energy-dependent and L shell-dependent inner boundary of the outer radiation belt during 37 isolated geomagnetic storms using observations from Van Allen Probes from 2013 to 2017. There are mutual transformations between "V-shaped" and "S-shaped" inner boundaries during different storm phases, resulting from the competition among electron loss, radial transport and local acceleration. The radial position, onset time, Est (the minimum energy at Lst where the inner boundary starts to exhibit an S-shaped form), and the radial width of S-shaped boundary (&#916;L) are quantitatively defined according to the formation of a reversed energy spectrum (electron flux going up with increasing energies from hundreds of keV to ~1 MeV) from a kappa-like spectrum (electron flux steeply falling with increasing energies). The case and statistical results present that (1) The inner boundary has repeatable features associated with storms: the inner boundary is transformed from S-shaped to V-shaped form in several hours during the storm commencement and main phase, and retains in the V-shaped form for several days until it evolves into S-shaped during late recovery phase; (2) &#916;L shows positive correlation with SYM-H index; (3) The duration of the V-shaped form is positively correlated with the storm intensity and the duration of the recovery phase; (4) The minimum energy Est are mainly distributed in the range of 100-550 keV. All these findings have important implications for understanding the dynamics of energetic electrons in the slot region and the outer radiation belt during geomagnetic storms.

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Association of radiation belt electron enhancements with earthward penetration of Pc5 ULF waves: a case study of intense 2001 magnetic storms

Annales Geophysicae ◽

10.5194/angeo-33-1431-2015 ◽

2015 ◽

Vol 33 (11) ◽

pp. 1431-1442 ◽

Cited By ~ 9

Author(s):

M. Georgiou ◽

I. A. Daglis ◽

E. Zesta ◽

G. Balasis ◽

I. R. Mann ◽

...

Keyword(s):

Radiation Belt ◽

Low Frequency ◽

Recovery Phase ◽

Wave Activity ◽

Magnetic Storms ◽

Ulf Waves ◽

Relativistic Electrons ◽

Outer Radiation Belt ◽

Magnetometer Arrays ◽

The One

Abstract. Geospace magnetic storms, driven by the solar wind, are associated with increases or decreases in the fluxes of relativistic electrons in the outer radiation belt. We examine the response of relativistic electrons to four intense magnetic storms, during which the minimum of the Dst index ranged from −105 to −387 nT, and compare these with concurrent observations of ultra-low-frequency (ULF) waves from the trans-Scandinavian IMAGE magnetometer network and stations from multiple magnetometer arrays available through the worldwide SuperMAG collaboration. The latitudinal and global distribution of Pc5 wave power is examined to determine how deep into the magnetosphere these waves penetrate. We then investigate the role of Pc5 wave activity deep in the magnetosphere in enhancements of radiation belt electrons population observed in the recovery phase of the magnetic storms. We show that, during magnetic storms characterized by increased post-storm electron fluxes as compared to their pre-storm values, the earthward shift of peak and inner boundary of the outer electron radiation belt follows the Pc5 wave activity, reaching L shells as low as 3–4. In contrast, the one magnetic storm characterized by irreversible loss of electrons was related to limited Pc5 wave activity that was not intensified at low L shells. These observations demonstrate that enhanced Pc5 ULF wave activity penetrating deep into the magnetosphere during the main and recovery phase of magnetic storms can, for the cases examined, distinguish storms that resulted in increases in relativistic electron fluxes in the outer radiation belts from those that did not.

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Electron flux changes in the outer radiation belt by radial diffusion during the storm recovery phase in comparison with the fully adiabatic evolution

Journal of Geophysical Research Atmospheres ◽

10.1029/2011ja016642 ◽

2011 ◽

Vol 116 (A9) ◽

pp. n/a-n/a ◽

Cited By ~ 17

Author(s):

Kyung-Chan Kim ◽

Dae-Young Lee ◽

Yuri Shprits ◽

Hee-Jeong Kim ◽

Ensang Lee

Keyword(s):

Radiation Belt ◽

Electron Flux ◽

Recovery Phase ◽

Radial Diffusion ◽

Adiabatic Evolution ◽

Outer Radiation Belt

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Effect of solar and magnetic activity on VHF scintillations near the equatorial anomaly crest

Annales Geophysicae ◽

10.5194/angeo-22-2849-2004 ◽

2004 ◽

Vol 22 (8) ◽

pp. 2849-2860 ◽

Cited By ~ 24

Author(s):

R. P. Singh ◽

R. P. Patel ◽

A. K. Singh

Keyword(s):

Solar Activity ◽

Solar Cycle ◽

Electric Fields ◽

Recovery Phase ◽

Magnetic Activity ◽

Magnetic Storms ◽

High Solar Activity ◽

Equatorial Anomaly ◽

Probability Of Occurrence

Abstract. The VHF amplitude scintillation recorded during the period January 1991 to December 1993 in the declining phase of a solar cycle and April 1998 to December 1999 in the ascending phase of the next solar cycle at Varanasi (geogr. lat.=25.3°, long.=83.0°, dip=37°N) have been analyzed to study the behavior of ionospheric irregularities during active solar periods and magnetic storms. It is shown that irregularities occur at arbitrary times and may last for <30min. A rise in solar activity increases scintillations during winter (November-February) and near equinoxes (March-April; September-October), whereas it depresses the scintillations during the summer (May-July). In general, the role of magnetic activity is to suppress scintillations in the pre-midnight period and to increase it in the post-midnight period during equinox and winter seasons, whilst during summer months the effect is reversed. The pre-midnight scintillation is sometimes observed when the main phase of Dst corresponds to the pre-midnight period. The annual variation shows suppression of scintillations on disturbed days, both during pre-midnight and post-midnight period, which becomes more effective during years of high solar activity. It is observed that for magnetic storms for which the recovery phase starts post-midnight, the probability of occurrence of irregularities is enhanced during this time. If the magnetic storm occurred during daytime, then the probability of occurrence of scintillations during the night hours is decreased. The penetration of magnetospheric electric fields to the magnetic equator affects the evolution of low-latitude irregularities. A delayed disturbance dynamo electric field also affects the development of irregularities.

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Average profiles of the solar wind and outer radiation belt during the extreme flux enhancement of relativistic electrons at geosynchronous orbit

Annales Geophysicae ◽

10.5194/angeo-26-1335-2008 ◽

2008 ◽

Vol 26 (6) ◽

pp. 1335-1339 ◽

Cited By ~ 16

Author(s):

R. Kataoka ◽

Y. Miyoshi

Keyword(s):

Solar Wind ◽

Large Scale ◽

Radiation Belt ◽

Dynamic Pressure ◽

Recovery Phase ◽

Geosynchronous Orbit ◽

Relativistic Electrons ◽

Outer Radiation Belt ◽

Flux Enhancement ◽

Solar Wind Structure

Abstract. We report average profiles of the solar wind and outer radiation belt during the extreme flux enhancement of relativistic electrons at geosynchronous orbit (GEO). It is found that seven of top ten extreme events at GEO during solar cycle 23 are associated with the magnetosphere inflation during the storm recovery phase as caused by the large-scale solar wind structure of very low dynamic pressure (<1.0 nPa) during rapid speed decrease from very high (>650 km/s) to typical (400–500 km/s) in a few days. For the seven events, the solar wind parameters, geomagnetic activity indices, and relativistic electron flux and geomagnetic field at GEO are superposed at the local noon period of GOES satellites to investigate the physical cause. The average profiles support the "double inflation" mechanism that the rarefaction of the solar wind and subsequent magnetosphere inflation are one of the best conditions to produce the extreme flux enhancement at GEO because of the excellent magnetic confinement of relativistic electrons by reducing the drift loss of trapped electrons at dayside magnetopause.

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High-speed stream driven inferences of global wave distributions at geosynchronous orbit: relevance to radiation-belt dynamics

Proceedings of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rspa.2010.0076 ◽

2010 ◽

Vol 466 (2123) ◽

pp. 3351-3362 ◽

Cited By ~ 20

Author(s):

Elizabeth A. MacDonald ◽

Lauren W. Blum ◽

S. Peter Gary ◽

Michelle F. Thomsen ◽

Michael H. Denton

Keyword(s):

High Speed ◽

Radiation Belt ◽

Recovery Phase ◽

Wave Activity ◽

Geosynchronous Orbit ◽

Relativistic Electrons ◽

Particle Interactions ◽

Early Recovery ◽

Emic Wave ◽

Major Loss

Three superposed epoch analyses of plasma data from geosynchronous orbit are compared to infer relative distributions of electromagnetic ion cyclotron (EMIC)- and whistler-mode wave instabilities. Both local-time and storm-time behaviours are studied with respect to dynamics of relativistic electrons. Using LANL-GEO particle data and a quasi-linear approximation for the wave growth allows us to estimate the instability of the two wave modes. This simple technique can allow powerful insights into wave–particle interactions at geosynchronous orbit. Whistler-wave activity peaks on the dayside during the early recovery phase and can continue to be above normal levels for several days. The main phase of all storms exhibits the most EMIC-wave activity, whereas in the recovery phase of the most radiation-belt-effective storms, a significantly suppressed level of EMIC activity is inferred. These key results indicate new dynamics relating to plasma delivery, source and response, but support generally accepted views of whistlers as a source process and EMIC-mode waves as a major loss contributor at geosynchronous orbit.

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