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Abstract Enabled by state‐of‐the‐art electric field measurements from the Van Allen Probes and careful calibration of the high‐quality data, we developed the first machine‐learning based inner‐magnetosphere electric field model, which coversL = 2.5–6.0 within 20 around the magnetic equator. The model output is the DC electric field perpendicular to the background magnetic field, including the poloidal and toroidal components. The most informative drivers, including the SYM‐H and AE indices and solar wind speed, are automatically identified during the model training process. The model input consists of these parameters along with time and spatial coordinates. The model successfully reproduces the storm‐time evolution of meso‐scale electric field structures, potentially related to subauroral polarization streams and dawnside auroral polarization streams. Given the growing recognition that meso‐scale electric field structures modulate the transport of high‐energy electrons, our model can incorporate these structures into studies of ring current and radiation belt dynamics. 

Abstract We present multi‐platform observations of plasma cloak, O+ outflows, kinetic Alfven waves (KAWs), and auroral oval for the geomagnetic storm on 17 March 2015. During the storm's main phase, we observed a generally symmetric equatorward motion of the auroral oval in both hemispheres, corresponding to the plasmasphere erosion and inward motion of the plasma sheet. Consequently, Van Allen Probes became immersed within the plasma sheet for extended hours and repeatedly observed correlated KAWs and O+ outflows. The KAWs contain adequate energy flux toward the ionosphere to energize the observed outflow ions. Adiabatic particle tracing suggests that the O+ outflows are directly from the nightside auroral oval and that the energization is through a quasi‐static potential drop. The O+ outflows from the nightside auroral oval were adequate (‐ #/‐s) and prompt (several minutes) to explain the newly formed plasma cloak, suggesting that they were a dominant initial source of plasma cloak during this storm. 

Abstract The Van Allen Probes Electric Fields and Waves (EFW) instrument provided measurements of electric fields and spacecraft floating potentials over a wide dynamic range from DC to 6.5 kHz near the equatorial plane of the inner magnetosphere between 600 km altitude and 5.8 Re geocentric distance from October 2012 to November 2019. The two identical instruments provided data to investigate the quasi-static and low frequency fields that drive large-scale convection, waves induced by interplanetary shock impacts that result in rapid relativistic particle energization, ultra-low frequency (ULF) MHD waves which can drive radial diffusion, and higher frequency wave fields and time domain structures that provide particle pitch angle scattering and energization. In addition, measurements of the spacecraft potential provided a density estimate in cold plasmas ( $$<20~\text{eV}$$ < 20 eV ) from 10 to $$3000~\text{cm}^{-3}$$ 3000 cm − 3 . The EFW instrument provided analog electric field signals to EMFISIS for wave analysis, and it received 3d analog signals from the EMFISIS search coil sensors for inclusion in high time resolution waveform data. The electric fields and potentials were measured by current-biased spherical sensors deployed at the end of four 50 m booms in the spacecraft spin plane (spin period $$\sim11~\text{sec}$$ ∼ 11 sec ) and a pair of stacer booms with a total tip-tip separation of 15 m along the spin axis. Survey waveform measurements at 16 and/or 32 S/sec (with a nominal uncertainty of 0.3 mV/m over the prime mission) were available continuously while burst waveform captures at up to 16,384 S/sec provided high frequency waveforms. This post-mission paper provides the reader with information useful for accessing, understanding and using EFW data. Selected science results are discussed and used to highlight instrument capabilities. Science quantities, data quality and error sources, and analysis routines are documented.