SAPS/SAID revisited: A causal relation to the substorm current wedge

Abstract

We present multispacecraft observations of enhanced flow/electric field channels in the inner magnetosphere and conjugate subauroral ionosphere, i.e., subauroral polarization streams (SAPS) near dusk and subauroral ion drifts (SAID) near midnight. The channels collocate with ring current (RC) injections lagging the onset of substorms by a few to ∼20 min, i.e., significantly shorter than the gradient‐curvature drift time of tens of keV ions. The time lag is of the order of the propagation time of reconnection‐injected hot plasma jets to the premidnight plasmasphere and the substorm current wedge (SCW) to dusk. The observations confirm and expand on the previous results on the SAID features that negate the paradigm of voltage and current generators. Fast‐time duskside SAPS/RC injections appear intimately related to a two‐loop circuit of the substorm current wedge (SCW2L). We suggest that the poleward electric field inherent in the SCW2L circuit, which demands closure of the Region 1 and Region 2 sense field‐aligned currents via meridional currents, is the ultimate cause of fast RC injections and SAPS on the duskside.

A New Empirical Model of the Subauroral Polarization Stream

“…However, this linear trend is not as pronounced for the lower geomagnetic activity levels ( A s y ‐ H index <60), indicating that the asymmetric ring current may not be the primary driver of SAPS during nonstorm conditions. Indeed, the various differences between disturbed time and quiet time SAPS presented in this paper support new theories suggesting alternative mechanisms for driving SAPS such as the inherent current closure in the SCW (Mishin et al, ).…”

Steve: The Optical Signature of Intense Subauroral Ion Drifts

“…The T e and v i measured coincident with Steve are both significantly higher than the values modeled by Sazykin et al (2002), suggesting that electron impact and ion-neutral frictional heating may both contribute to the red emissions of Steve. The presence of such suprathermal electrons in SAID events has been reported from Defense Meteorological Satellite Program (DMSP) observations in the topside ionosphere and Combined Release and Radiation Effects Satellite (CRRES), Time History of Events and Macroscale Interactions during Substorms (THEMIS), Van Allen Probes (VAP), and Polar observations in the conjugate plasmasphere (e.g., Mishin, 2013;Mishin et al, 2017). The purple observed in traditional aurora is caused by the deexcitation of N + 2 .…”

The Magnetosphere‐Ionosphere Electron Precipitation Dynamics and Their Geospace Consequences During the 17 March 2013 Storm

“…Wolf (1970) and Vasyliunas (1970) used the ionospheric Ohm's law to calculate the electric field distribution governing magnetospheric plasma circulation. al., 1993;Zheng et al, 2008;Huba et al, 2017;Mishin et al, 2017), and plasma sheet fast-flow dynamics (Zhang et al, 2012). al., 1993;Zheng et al, 2008;Huba et al, 2017;Mishin et al, 2017), and plasma sheet fast-flow dynamics (Zhang et al, 2012).…”