Superposed epoch analysis of the ionospheric convection evolution during substorms: onset latitude dependence

Abstract

Abstract. Using data from the Super Dual Auroral Radar Network (SuperDARN) we investigate the ionospheric convection response to magnetospheric substorms. Substorms were identified using the Far Ultraviolet (FUV) instrument on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft, and were then binned according to the magnetic latitude of their onset. A superposed epoch analysis of the ionospheric convection patterns for each onset-latitude bin was then performed using radar data for the interval 60 min before onset to 90 min after. It is found that lower onset-latitude substorms are associated with generally more enhanced convection than the higher latitude substorms, although they suffer from a significant localised reduction of the flow in the midnight sector during the expansion phase. Higher-latitude substorms are associated with a significant and rapid increase in the nightside convection following substorm onset, with all onset-latitude bins showing an enhancement over onset values by ∼60 min into the expansion phase. A rudimentary inspection of the concurrent auroral evolution suggests that the duration of the flow reduction following substorm onset is dependent on the strength and duration of the expansion phase aurora and its associated conductivity enhancement.

Substorms and polar cap convection: the 10 January 2004 interplanetary CME case

“…Our result on this point is consistent with the previously published radar observations by Grocott et al (2010). They found "a lack of IMF B y -control in the nightside auroral zone.…”

Substorm triggering by new plasma intrusion: THEMIS all‐sky imager observations

“…The MLT distribution given in Figure 5d shows that onset tends to occur preferably in the premidnight sector. The median onset MLT, 22.6 h with a standard deviation of 1.1 h, is consistent with statistical studies performed using global auroral observations from space [ Frey et al , 2004; Grocott et al , 2009]. The locations of the poleward and equatorward boundaries are consistent with the study by Gjerloev et al [2008].…”

Dynamic subauroral ionospheric electric fields observed by the Falkland Islands radar during the course of a geomagnetic storm

“…One aspect of the complexity of substorm electrodynamics concerns the coupling of auroral zone electric fields, associated with convection and the Harang discontinuity [e.g., Grocott et al , 2006; Zou et al , 2009a, 2009b; Grocott et al , 2010], to subauroral electric fields, discussed below. A variety of observations of subauroral electric fields have been reported, identified by a variety of instrumentation during various levels of geomagnetic activity and referred to by an abundant array of names including polarization jets (PJ) [ Galperin et al , 1973], subauroral ion drifts (SAID) [ Spiro et al , 1979], substorm associated radar auroral surges (SARAS) [ Freeman et al , 1992], subauroral electric fields (SAEF) [ Karlsson et al , 1998], subauroral polarization streams (SAPS) [ Foster and Burke , 2002] and auroral‐westward flow channels (AWFC) [ Parkinson et al , 2003].…”