Shock aurora: FAST and DMSP observations

Abstract

[1] Global signatures of the aurora caused by interplanetary shocks/pressure pulses have been studied in recent years using ultraviolet imager data from polar orbiting spacecraft. The signatures include the occurrence of the aurora first near local noon and then propagation antisunward along the auroral oval at very high speeds. To better understand the mechanisms of particle precipitation, in this paper we study shock auroras using nearEarth observations of the FAST and DMSP satellites. We have studied the events that occurred during 1996-2000 where FAST and/or DMSP crossed the dawnside or duskside auroral zone within 10 min after shocks/pressure pulses arrived at the nose of the magnetopause. It is found that the electron precipitation increased significantly above the dawnside and duskside auroral oval zone after the shock/pressure pulse arrivals. The precipitation structure is low-energy electrons (<$1 keV) at higher latitudes ($75°-83°I LAT within 0600-0900 MLT) and high-energy electrons ($1-10 keV) at lower latitudes ($65°-79°ILAT) of the auroral zone. There are a few degrees (1°-4°ILAT) of overlap between these two categories of precipitated electrons. The precipitation of low-energy electrons was along highly structured field-aligned currents. The precipitation of the high-energy electrons was highly isotropic filling the loss cone. Possible mechanisms of field-aligned current generation are some dynamic processes occurring on the dayside magnetopause, such as magnetic shearing, magnetopause perturbation, magnetic reconnection, and Alfvén wave generation. Adiabatic compression might have caused the high-energy electron precipitation. On the basis of observations of FAST and DMSP, shock auroras are speculated to be diffuse auroras at the lower latitudes of the dayside auroral oval and discrete auroras on the poleward boundary of the oval with a few latitude degree overlap of the two types of auroras.

Evolution of the current system during solar wind pressure pulses based on aurora and magnetometer observations

“…Thus, the diffuse auroral intensification would be caused by enhanced ion precipitation in the downward R2 FAC. This interpretation is consistent with global imaging (Zhang et al 2008;Motoba et al 2009;Holmes et al 2014) and particle observations (Egeland et al 1994;Zhou et al 2003). Figure 3 shows the equivalent current patterns from the magnetometer data in the dayside Northern Hemisphere.…”

Properties of dayside nonlinear rising tone chorus emissions at large L observed by GEOTAIL

“…Tim-ing of the chorus observation correspond roughly to time delays of substorm electrons drifting from the midnight sector. There is a possibility that magnetospheric compression due to the solar wind ram pressure enhances chorus generation at large L-shells (Zhou et al, 2003). Chorus can be intensified by drift-shell splitting.…”

Decrease of auroral intensity associated with reversal of plasma convection in response to an interplanetary shock as observed over Zhongshan station in Antarctica

“…The large-scale auroral transient signatures in response to the IP shock (i.e., shock aurora) were analyzed by several authors using satellite observations [e.g., Zhou and Tsurutani, 1999;Sibeck et al, 1999;Zhou et al, 2003;Laundal and Østgaard, 2008]. Shock aurora observed from satellites [e.g., Zhou and Tsurutani, 1999;Tsurutani et al, 2001] show that the aurora immediately brightens near local noon at the time of the shock arrival.…”