Global and local Joule heating during substorms in St. Patrick’s Day 2015 geomagnetic storm

Abstract

Abstract The first super storm of solar cycle 24 occurred on “St. Patrick’s Day” (17 March 2015), with a minimum Dst level of − 223 nT. Five major substorms in this super storm were selected, with minimum values of local electrojet index (IL) ranging from − 1662 to − 673 nT. The selected substorms are all in the 22:00 MLT–06:00 MLT sector of the auroral oval region showing associated Pi2s and negative bays in the H-component of magnetograms, derived from the IMAGE magnetometer longitudinal (Fennoscandia) chain. The solar wind energy input is estimated as time integral of Akasofu’s epsilon parameter, determined from the SuperMAG magnetometer. The local ionospheric Joule heating (local JH) rate, in the midnight or post-midnight sectors, is estimated using a modified form of Ahn’s empirical conversion. The Global ionospheric Joule heating rate in the northern hemisphere (global JH) is taken from OpenGGCM model. For the substorm in the main phase of the superstorm, the local JH consumes only 9% (8%, if the IL is replaced by AL index in the empirical conversion relation) of the global JH. However, 40–86% (39–48%, if the IL is replaced by AL index in the empirical conversion relation) of global JH is consumed as local JH for the remaining substorms.

Keywords

• Geomagnetic storms
• Substorms
• Pi2 pulsations
• Ionospheric Joule heating