Impact of Significant Time‐Integrated Geomagnetic Activity on 2‐MeV Electron Flux

Abstract

We explore the impact on the outer radiation belt of significant time-integrated ap events of continuously elevated geomagnetic activity, making use of Van Allen Probes measurements in 2013-2017. We show that most high peaks of 1.8-MeV electron flux occur during the 10 days immediately following such events, with stronger events leading to higher flux. Events larger than 800 nT•hr are always followed by a high peak of flux in the heart of the outer radiation belt. They lead to 10-day-averaged 1.8-MeV electron fluxes of the order of 10 6 e/cm 2 /sr/s/MeV in this region and 8 × 10 4 e/cm 2 /sr/s/MeV near geostationary orbit. Accordingly, they can be considered as reliable precursors of high peaks of 2-MeV electron flux throughout the outer belt. We demonstrate that the flux peaks following such significant events can be parameterized by different geomagnetic indices at different radial locations in 2013-2017. Comparisons between the corresponding modeled flux peaks and observations show a reasonable agreement for both the timing, duration, and level of the peaks with 2015 data from the Van Allen Probes and also with 2002-2012 data from Global Positioning System satellites and 2003-2016 data from Geostationary Operational Environmental Satellites, provided that dropouts are taken into account via an appropriate threshold on solar wind dynamic pressure. Plain Language Summary Considering significant events of prolonged and elevated geomagnetic activity measured at middle-latitude stations, we examine their effects on megaelectron volt electron fluxes that represent an important hazard for satellites throughout the outer radiation belt. Using measurements performed by the Van Allen Probes in 2013-2017, we find that high peaks of 1.8-MeV electron flux appear in the immediate aftermath of all events in the heart of the outer radiation belt and last about 10 days. Such events can therefore be considered as reliable precursors of high flux peaks. The statistical dependence of flux peaks on different measures of precursor event strength and radial distance is obtained. The reliability of such a description over the long term is tested by comparisons with earlier measurements from other satellites in 2002-2012, further taking dropouts into account. These results should be useful for better understanding the effects of geomagnetic disturbances on megaelectron volt electrons and to improve forecasts of the timing and level of such peaks of 2-MeV electron flux.

Dynamical Properties of Peak and Time‐Integrated Geomagnetic Events Inferred From Sample Entropy

“…Accordingly, the size (in hours) of the sliding time window must not be too wide compared with event duration, while still encompassing most of the strongest events. Geomagnetic storms and time‐integrated ( ) events of generally last less than 10 days (Mourenas et al, ; Xie et al, ). Therefore, picking hr is a reasonable choice (Donner et al, ; Yentes et al, ).…”

“…It is determined by both solar wind forcing and internal magnetospheric processes (Daglis et al, ; Kozyra & Liemohn, ; O'Brien & McPherron, ). But alone cannot provide a full account of the complexity of geomagnetic storms, nor can it provide an appropriate measure of the strength of all strong disturbances induced by the solar wind (Borovsky, ; Borovsky & Shprits, ; Mourenas et al, ). The index (varying linearly from 0 to 400) is obtained from 3‐hr measurements of the disturbance range of the horizontal component of the Earth's magnetic field at middle latitude stations; it can serve as a proxy of magnetospheric convection and substorm‐associated field‐aligned currents flowing in and out of the ionosphere (Borovsky & Shprits, ; Mayaud, ; Thomsen, ).…”

“…Studies aiming at providing forecasts of the radiation belts have mostly investigated the correlations between indices of geomagnetic activity and some solar wind parameters and measured electron fluxes at a given location (Borovsky, , ). However, recent works have shown that cumulative effects of geomagnetic activity can sometimes be more important for predicting relativistic electron fluxes and geomagnetically induced currents than instantaneous or peak values of geomagnetic activity (Borovsky, ; Hajra et al, ; Lotz & Danskin, ; Mourenas et al, , ). Moreover, different investigations of the 1‐hr index, of the 1‐hr index, and of the 1‐min SYM‐H index have demonstrated that quiet times and geomagnetic storms correspond in general to different dynamical regimes, with more persistence (Balasis et al, ; Uritsky & Pudovkin, ) and a reduced entropy (Balasis et al, ; Donner et al, ) during storms.…”

“…Here, we expand upon previous pioneering entropy studies (Balasis et al, , ; Donner et al, ; Johnson et al, ) that mainly focused on the instantaneous 1‐hr index, by additionally considering other indices of geomagnetic activity (such as , ) that are often more appropriate than for describing strong increases of fluxes of ‐ to ‐MeV satellite‐killer electrons in the radiation belts (Borovsky & Shprits, ; Mourenas et al, ), by studying their entropy variations as a function of the peak or time‐integrated strengths of geomagnetic events and by examining the correlations between their entropies and the entropy of energetic particle fluxes measured by satellites at various locations. This will allow us to explore the possible roles of physical system organization and stochasticity in the development of large and long‐duration events at different geomagnetic latitudes that affect different locations in the radiation belts.…”

Understanding Electron Dropout Echoes Induced by Interplanetary Shocks: Test Particle Simulations

“…These violent solar phenomena can drive magnetic storms, during which electron radiation belt can vary drastically (e.g., Ganushkina et al, 2015;Katsavrias et al, 2019;Mourenas et al, 2019;Turner et al, 2019, and references therein). The impingement of an IP shock can suddenly compress the magnetosphere, further leading to acceleration and transport of energetic electrons.…”