Relativistic electron flux responses in the inner magnetosphere are investigated for 28 magnetic storms driven by corotating interaction region (CIR) and 27 magnetic storms driven by coronal mass ...ejection (CME), using data from the Relativistic Electron‐Proton Telescope instrument on board Van Allen Probes from October 2012 to May 2017. In this present study we analyze the role of CIRs and CMEs in electron dynamics by sorting the electron fluxes in terms of averaged solar wind parameters, L‐values, and energies. The major outcomes from our study are the following: (i) At L = 3 and E = 3.4 MeV, for >70% cases the electron flux remains stable, while at L = 5, for ~82% cases it changes with the geomagnetic conditions. (ii) At L = 5, ~53% of the CIR storms and 30% of the CME storms show electron flux increase. (iii) At a given L‐value, the tendency for the electron flux variation diminishes with the increasing energies for both categories of storms. (iv) In case of CIR‐driven storms, the electron flux changes are associated with changes in Vsw and Sym‐H. (v) At L ~ 3, CME storms show increased electron flux, while at L ~ 5, CIR storms are responsible for the electron flux enhancements. (vi) During CME‐ and CIR‐driven storms, distinct electron flux variations are observed at L = 3 and L = 5.
Key Points
At L = 5, 53% of the CIR storms and 30% of the CME storms show electron flux increase
Relativistic electron flux variations at L = 5 is largely independent of geomagnetic storm strength but strongly depends upon averaged Vsw and IMF Bz
At L = 3, >71% geomagnetic storms show no remarkable electron flux variations, irrespective of the storm driver
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Using Van Allen Probes Energetic Particle, Composition, and Thermal Plasma‐Relativistic Electron‐Proton Telescope (ECT‐REPT) observations, we performed a statistical study on the effect of ...geomagnetic storms on relativistic electrons fluxes in the outer radiation belt for 78 storms between September 2012 and June 2016. We found that the probability of enhancement, depletion, and no change in flux values depends strongly on L and energy. Enhancement events are more common for ∼2 MeV electrons at L ∼ 5, and the number of enhancement events decreases with increasing energy at any given L shell. However, considering the percentage of occurrence of each kind of event, enhancements are more probable at higher energies, and the probability of enhancement tends to increases with increasing L shell. Depletion are more probable for 4–5 MeV electrons at the heart of the outer radiation belt, and no‐change events are more frequent at L < 3.5 for E ∼ 3 MeV particles. Moreover, for L > 4.5 the probability of enhancement, depletion, or no‐change response presents little variation for all energies. Because these probabilities remain relatively constant as a function of radial distance in the outer radiation belt, measurements obtained at geosynchronous orbit may be used as a proxy to monitor E≥1.8 MeV electrons in the outer belt.
Key Points
Statistical study on the effect of storms on relativistic electrons fluxes in the radiation belts
Probability of enhancement, depletion, and no change in flux values depends strongly on L and energy
Measurements at GEO orbit may be used as a proxy to monitor E greater than or equal to 1.8 MeV electrons in the outer belt
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
The Van Allen radiation belts are two regions encircling the Earth in which energetic charged particles are trapped inside the Earth's magnetic field. Their properties vary according to solar ...activity and they represent a hazard to satellites and humans in space. An important challenge has been to explain how the charged particles within these belts are accelerated to very high energies of several million electron volts. Here we show, on the basis of the analysis of a rare event where the outer radiation belt was depleted and then re-formed closer to the Earth, that the long established theory of acceleration by radial diffusion is inadequate; the electrons are accelerated more effectively by electromagnetic waves at frequencies of a few kilohertz. Wave acceleration can increase the electron flux by more than three orders of magnitude over the observed timescale of one to two days, more than sufficient to explain the new radiation belt. Wave acceleration could also be important for Jupiter, Saturn and other astrophysical objects with magnetic fields.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Radiation belt electrons undergo frequent acceleration, transport, and loss processes under various physical mechanisms. One of the most prevalent mechanisms is radial diffusion, caused by the ...resonant interactions between energetic electrons and ULF waves in the Pc4‐5 band. An indication of this resonant interaction is believed to be the appearance of periodic flux oscillations. In this study, we report long‐lasting, drift‐periodic flux oscillations of relativistic and ultrarelativistic electrons with energies up to ∼7.7 MeV in the outer radiation belt, observed by the Van Allen Probes mission. During this March 2017 event, multi‐MeV electron flux oscillations at the electron drift frequency appeared coincidently with enhanced Pc5 ULF wave activity and lasted for over 10 h in the center of the outer belt. The amplitude of such flux oscillations is well correlated with the radial gradient of electron phase space density (PSD), with almost no oscillation observed near the PSD peak. The temporal evolution of the PSD radial profile also suggests the dominant role of radial diffusion in multi‐MeV electron dynamics during this event. By combining these observations, we conclude that these multi‐MeV electron flux oscillations are caused by the resonant interactions between electrons and broadband Pc5 ULF waves and are an indicator of the ongoing radial diffusion process during this event. They contain essential information of radial diffusion and have the potential to be further used to quantify the radial diffusion effects and aid in a better understanding of this prevailing mechanism.
Key Points
Long‐lasting, drift‐periodic flux oscillations of 1.8–7.7 MeV electrons in the radiation belt are reported using Van Allen Probes data
Flux oscillations appeared coincidently with enhanced Pc5 ULF waves with amplitude well correlated with phase space density radial gradient
These flux oscillations indicate the resonant interactions between electrons and broadband Pc5 ULF waves
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Recent observations show that the decay rate of relativistic electrons measured at low altitudes in the slot region at L = 2 is an order of magnitude shorter than theoretical estimates based on CRRES ...wave data. Here we compare the decay rates of 2–6 MeV electrons measured at low altitudes by the SAMPEX spacecraft with those derived from CRRES wave observations. We show that pitch angle scattering by plasmaspheric hiss (0.1 < f < 2 kHz) is the dominant process responsible for electron loss in the outer slot region (2.4 < L < 3.0), but hiss alone cannot account for the observed loss timescales at lower L. Although SAMPEX samples small equatorial pitch angles (αeq ≈ 18°), this is not the dominant reason for the different timescales. We find that the decay of 2–6 MeV electrons measured by SAMPEX in the inner slot region (2.0 < L < 2.4) is most likely due to the combined effects of hiss and guided whistlers propagating with small wave normal angles. Unguided whistlers have little or no effect on the loss timescales. Magnetosonic waves may be as important as guided whistlers for electron loss under active conditions. Guided whistlers and fast magnetosonic waves increase the diffusion rates in a “bottleneck region” near αeq = 75°, enabling electrons with larger pitch angles to diffuse into the loss cone more effectively and hence the entire distribution function decays more rapidly. Even though the power of guided whistlers and magnetosonic waves may be two orders of magnitude less than hiss, they play a very important role in electron loss in the inner slot region.
The Relativistic Electron-Proton Telescope (REPT) instruments were designed to measure ∼2 to >18 MeV electrons and ∼18 to > 115 MeV protons as part of the science payloads onboard the dual Radiation ...Belt Storm Probes (RBSP) spacecraft. The REPT instruments were turned on and configured in their science acquisition modes about 2 days after the RBSP launch on 30 August 2012. The REPT-A and REPT-B instruments both operated flawlessly until mission cessation in 2019. This paper reviews briefly the REPT instrument designs, their operational performance, relevant mode changes and trending over the course of the mission, as well as pertinent background effects (and recommended corrections). A substantial part of this paper highlights discoveries and significant advancement of our understanding of physical-processes obtained using REPT data. We do this for energetic electrons primarily in the outer Van Allen belt and for energetic protons in the inner Van Allen zone. The review also describes several ways in which REPT data were employed for important space weather applications. The paper concludes with assessments of ways that REPT data might further be exploited to continue to advance radiation belt studies. The paper also discusses the pressing and critical need for the operational continuation of REPT-like measurements both for science and for space situational awareness.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Multi‐MeV electron drift‐periodic flux oscillations observed in Earth's radiation belts indicate radial transport and energization/de‐energization of these radiation belt core populations. Using ...multi‐year Van Allen Probes observations, a statistical analysis is conducted to understand the characteristics of this phenomenon. The results show that most of these flux oscillations result from resonant interactions with broadband ultralow frequency (ULF) waves and are indicators of ongoing radial diffusion. The occurrence frequency of flux oscillations is higher during high solar wind speed/dynamic pressure and geomagnetically active times; however, a large number of them were still observed under mild to moderate solar wind/geomagnetic conditions. The occurrence frequency is also highest (up to ∼30%) at low L‐shells (L∗∼3−4 ${L}^{\ast }\sim 3-4$) under various geomagnetic activity, suggesting the general presence of broadband ULF waves and radial diffusion at low L‐shells even during geomagnetically quiet times and showing the critical role of the electron phase space density radial gradient in forming drift‐periodic flux oscillations.
Plain Language Summary
Earth's radiation belts contain 100s of keV–10 MeV electrons which pose great threats to the avionics and humans in space. Understanding their dynamics is critical due to both scientific interests and practical needs. Periodic flux oscillations of multi‐MeV electrons at their drift frequencies have been previously observed in Earth's radiation belts. These flux oscillations are believed to be indicators of the radial transport of these electrons and contain critical information of their energization processes. Using Van Allen Probes observations, a statistical analysis is conducted to further understand this phenomenon and associated mechanisms. It is shown that the majority of observed flux oscillations result from resonant interactions between multi‐MeV electrons and broadband ultralow frequency (ULF) waves, which lead to radial diffusion, one of the most important mechanisms causing radiation belt electron acceleration/loss. These flux oscillations preferentially occur under active solar wind conditions and geomagnetic activity. They also occur more often at lower altitudes, which is due to the steeper radial gradient of the electron distribution closer to the Earth. This indicates the general presence of broadband ULF waves and radial diffusion at low altitudes and suggests the critical role of the radial gradient of the electron distribution in forming these flux oscillations.
Key Points
Most multi‐MeV electron drift‐periodic flux oscillations in the outer belt result from resonant interaction with broadband ultralow frequency waves
These flux oscillations preferentially occur during high solar wind speed/dynamic pressure and geomagnetically active times
The occurrence rate of these flux oscillations is highest at L*∼ 3–4 due to higher phase space density radial gradients at lower L
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
Fast reverse shocks (FRSs) cause the magnetosphere to expand, by contrast to the well-known compressions caused by the impact of fast forward shocks (FFS). Usually, FFSs are more ...geoeffective than FRSs, and consequently the inner magnetosphere dynamic responses to both shock types can be quite different. In this study, we investigate for the first time the radiation belt response to an FRS impact using multi-satellite observations and numerical simulations. Spacecraft on the dayside observed decreases in magnetic field strength and energetic (∼40–475 keV) particle fluxes. Timing analysis shows that the magnetic field signature propagated from the dayside to the nightside magnetosphere. Particles with different energies vary simultaneously at each spacecraft, implying a non-dispersive particle response to the shock. Spacecraft located at lower L-shells did not record any significant signatures. The observations indicate a local time dependence of the response associated with the shock inclination, with the clearest signatures being observed in the dusk–midnight sector. Simulations underestimate the amplitude of the magnetic field variations observed on the nightside. The observed decreases in the electron intensities result from a combination of radial gradient and adiabatic effects. The radial gradients in the spectral index appear to be the dominant contributor to the observed variations of electrons seen on the dayside (near noon and dusk) and on the nightside (near midnight). This study shows that even an FRS can affect the radiation belts significantly and provides an opportunity to understand their dynamic response to a sudden expansion of the magnetosphere.
In this study we examine the ability of protons of solar origin to access the near‐equatorial inner magnetosphere. Here we examine four distinct solar proton events from 20–200 MeV, concurrent with ...both quiet time and storm time conditions using proton data from the ACE satellite in the solar wind upstream of Earth and data from the Relativistic Electron Proton Telescope (REPT) instrument aboard Van Allen Probes. We examine the direct flux correspondence between interplanetary space and the inner magnetosphere. Small substructures in interplanetary space are observable in the REPT flux profiles, which can penetrate down to L values of ≤4. Furthermore, there are orbit‐to‐orbit variations in the west‐to‐east anisotropic flux ratios. The anisotropic flux ratios are used as a proxy for cutoff energies and display cutoff variations with L shell and energy. The dependence of the anisotropic flux ratio on Dst values is shown. The results paint a picture of highly dynamic spatial and temporal proton cutoff rigidities in the near‐equatorial inner magnetosphere.
Key Points
Small flux substructures in interplanetary space are observed in the inner magnetosphere
West‐to‐east flux ratios are used as a proxy for cutoff location and energy
West‐to‐east flux ratios are highly dynamic from orbit to orbit and respond quickly to magnetospheric changes
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
10.
Space Plasma Physics: A Review Tsurutani, Bruce T.; Zank, Gary P.; Sterken, Veerle J. ...
IEEE transactions on plasma science,
07/2023, Volume:
51, Issue:
7
Journal Article
Peer reviewed
Open access
Owing to the ever-present solar wind, our vast solar system is full of plasmas. The turbulent solar wind, together with sporadic solar eruptions, introduces various space plasma processes and ...phenomena in the solar atmosphere all the way to Earth's ionosphere and atmosphere and outward to interact with the interstellar media to form the heliopause and termination shock. Remarkable progress has been made in space plasma physics in the last 65 years, mainly due to sophisticated in situ measurements of plasmas, plasma waves, neutral particles, energetic particles, and dust via space-borne satellite instrumentation. Additionally, high-technology ground-based instrumentation has led to new and greater knowledge of solar and auroral features. As a result, a new branch of space physics, i.e., space weather, has emerged since many of the space physics processes have a direct or indirect influence on humankind. After briefly reviewing the major space physics discoveries before rockets and satellites (<xref ref-type="sec" rid="sec1">Section I ), we aim to review all our updated understanding on coronal holes, solar flares, and coronal mass ejections, which are central to space weather events at Earth (<xref ref-type="sec" rid="sec2">Section II ), solar wind (<xref ref-type="sec" rid="sec3">Section III ), storms and substorms (<xref ref-type="sec" rid="sec4">Section IV ), magnetotail and substorms, emphasizing the role of the magnetotail in substorm dynamics (<xref ref-type="sec" rid="sec5">Section V ), radiation belts/energetic magnetospheric particles (<xref ref-type="sec" rid="sec6">Section VI ), structures and space weather dynamics in the ionosphere (<xref ref-type="sec" rid="sec7">Section VII ), plasma waves, instabilities, and wave-particle interactions (<xref ref-type="sec" rid="sec8">Section VIII ), long-period geomagnetic pulsations (<xref ref-type="sec" rid="sec9">Section IX ), auroras (<xref ref-type="sec" rid="sec10">Section X ), geomagnetically induced currents (GICs, <xref ref-type="sec" rid="sec11">Section XI ), planetary magnetospheres and solar/stellar wind interactions with comets, moons and asteroids (<xref ref-type="sec" rid="sec12">Section XII ), interplanetary discontinuities, shocks and waves (<xref ref-type="sec" rid="sec13">Section XIII ), interplanetary dust (<xref ref-type="sec" rid="sec14">Section XIV ), space dusty plasmas (<xref ref-type="sec" rid="sec15">Section XV ), and solar energetic particles and shocks, including the heliospheric termination shock (<xref ref-type="sec" rid="sec16">Section XVI ). This article is aimed to provide a panoramic view of space physics and space weather.
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