Solar wind impacts on growth phase duration and substorm intensity: A statistical approach

Abstract

A statistical survey of 379 interplanetary magnetic field (IMF) southward turning events during the time period from 1995 to 2011 is performed to study the impact of solar wind conditions on the substorm growth phase duration and intensity. Substorm growth phase persists from several minutes up to 2-3 h, and its duration is mainly controlled by solar wind conditions. The larger dayside reconnection E-field and solar wind speed are, the shorter the growth phase will be. The lower limits of solar wind reconnection E-field and bulk speed for substorm occurrence are found to be 0.6 mV/m and 280 km/s, respectively. Similarly, the substorm intensity is linearly correlated to the dayside reconnection E-field. However, it seems to be independent of the amount of dayside geomagnetic flux reconnected and solar wind energy entered into the magnetosphere during the growth phase. Furthermore, all the events are divided into three groups for different averages of dayside reconnection E-field during the growth phase (EKL̄): (1) 0.0 ≤EKL̄<1.5 mV/m; (2) 1.5≤EKL̄<2.5 mV/m; and (3) EKL̄≥2.5mV/m, and the geometric means of growth phase duration and auroral power maximum for these three groups are 91 min, 62 min, 32 min, and 35 GW, 51 GW, 74 GW, respectively. ©2013. American Geophysical Union. All Rights Reserved.