The evolution of ring current ion energy density and energy content during geomagnetic storms based on Van Allen Probes measurements

Abstract

Enabled by the comprehensive measurements from the Magnetic Electron Ion Spectrometer (MagEIS), Helium Oxygen Proton Electron mass spectrometer (HOPE), and Radiation Belt Storm Probes Ion Composition Experiment (RBSPICE) instruments onboard Van Allen Probes in the heart of the radiation belt, the relative contributions of ions with different energies and species to the ring current energy density and their dependence on the phases of geomagnetic storms are quantified. The results show that lower energy (<50 keV) protons enhance much more often and also decay much faster than higher‐energy protons. During the storm main phase, ions with energies <50 keV contribute more significantly to the ring current than those with higher energies; while the higher‐energy protons dominate during the recovery phase and quiet times. The enhancements of higher‐energy proton fluxes as well as energy content generally occur later than those of lower energy protons, which could be due to the inward radial diffusion. For the 29 March 2013 storm we investigated in detail that the contribution from O+ is ~25% of the ring current energy content during the main phase and the majority of that comes from <50 keV O+. This indicates that even during moderate geomagnetic storms the ionosphere is still an important contributor to the ring current ions. Using the Dessler‐Parker‐Sckopke relation, the contributions of ring current particles to the magnetic field depression during this geomagnetic storm are also calculated. The results show that the measured ring current ions contribute about half of the Dst depression.

Variation of Solar Wind Parameters Along With the Understanding of Energy Dynamics Within the Magnetospheric System During Geomagnetic Disturbances

“…The horizontal axis represents the scale in minutes and the vertical axis represents the crosscorrelation coefficient. So, even when there is no magnetic reconnection happening, the protons which are more active during the quietest period, present in the inner ionosphere, trigger the ring current that assists in depression of SYM-H value and positive correlation with magnetospheric energy deposition Ur, Uj, and Ua (Zhao et al, 2015). The plot is not symmetric with more inclination in the negative side of time scale.…”

“…Other than geomagnetic depression, such activity cause life-threatening power outages and satellite damage, communication failures and navigational problems (Lakhina & Tsurutani, 2016). The ring current is a near equatorial electric current flowing toroidally around the Earth, formed by charge particle pressure gradients and drift motion (Zhao et al, 2015). These currents lead to deposition of energy in different forms such as ring current energy, joule heating, and auroral precipitation.…”

Ion Energies Dominating Energy Density in the Inner Magnetosphere: Spatial Distributions and Composition, Observed by Arase/MEP‐i

“…Zhao et al (2015) showed that energy ranges that make the dominant contribution from H+ to the total energy density are higher at L = 3 and L = 4 than at L = 5 and 5.8 during a moderate storm on 29 March 2017. The spatial characteristics of contributing energies can be explained by adiabatic transport of plasma sheet ions during which lower-energy ions can penetrate more deeply into the inner magnetosphere than higher-energy ones due to relatively lower magnetic field drifts (i.e., curvature and gradient-B drifts).…”

Space Weather Effects Produced by the Ring Current Particles

“…This perturbation can be considered as a rough equivalent to the Dst-index if it is assumed (Carovillano and Siscoe 1973) that it is close to the perturbation averaged around the equator of the Earth. The DPS relation was used in numerous studies for Dst-index estimates from modeling and observations and related ring current dynamics (e.g., Greenspan and Hamilton 2000;Ebihara and Ejiri 2000;Fok et al 2001b;Jordanova et al 2012;Ganushkina et al 2012;Katus et al 2015;Zhao et al 2015). However, the Dst-index contains contributions from many other sources than the azimuthally symmetric ring current and their contributions can be significant or even largest during disturbed conditions.…”

“…Although, the early measurements of the ring current particles were made onboard OGO 3 (e.g., Frank 1967), Explorer 45 (e.g., Smith and Hoffman 1974) and CRRES missions (e.g., Grande et al 1997;Friedel and Korth 1997), the first mission, which clarified the detailed picture of the ring current energy and composition was the AMPTE mission of the late 1980s (e.g., Lui et al 1987;Lui and Hamilton 1992;De Michelis et al 1997). Extensive observations of the ring current were done by the most recent Van Allen Probes mission (e.g., Zhao et al 2015;Gkioulidou et al 2016;Kistler et al 2016;Shi et al 2016;Menz et al 2017). …”