Categorization of Substorm Triggering Mechanism based on the Ground Observations

Abstract

During a typical Akasofu-type of substorm, a southward component of IMF Bz is a necessary condition prior to the onset. However, there are evidences which show that sudden impulse, if strong enough, can also trigger substorms as in the case of 21st January 2005 supersubstorm event. The Akasofu-type substorm and impulse-induced substorm differ in terms of their occurrence mechanism and ground-based observations such as CNA, visual aurora and auroral electrojet enhancement. A question then arises is how these signatures vary when both sudden impulse and a southward component of IMF Bz are present prior to the onset. In order to account for the same, we analyze two substorm events of 05th April 2010 and 22nd June 2015. The substorm onsets in these cases not just coincide with the sudden impulse but also there is a presence of a southward component of IMF Bz prior to the onset. The present study accounts for the similarities and differences in the ground observations between IMF Bz induced substorms, impulse-induced substorms. We have tried to examine the relative dominance of these two factors in substorm onset in terms of observed features based on ground and satellite measurements. If the pressure pulse is very high, precipitation via viscous interaction becomes more feasible leading to precipitation centred near the local time sectors far away from the usual midnight. For low-pressure pulse, precipitation through night side magnetic reconnection dominates, which is in line with the usual Akasofu-type of substorm.