Effects of interplanetary shock inclinations on nightside auroral power intensity

TL;DR

This study analyzes how the inclination of interplanetary shocks affects nightside auroral power intensity, revealing that shocks aligned with the Sun-Earth line cause more intense auroral activity due to stronger magnetospheric compression.

Contribution

It introduces a large statistical analysis linking shock impact angles and speeds to auroral power, highlighting the importance of shock orientation in geomagnetic responses.

Findings

High auroral power occurs with shocks aligned parallel to the Sun-Earth line.

Strong shocks with high speeds induce more intense auroral activity.

Symmetric magnetospheric compression favors auroral power release.

Abstract

We derive fast forward interplanetary (IP) shock speeds and impact angles to study the geoeffectivness of 461 IP shocks that occurred from January 1995 to December 2013 using ACE and WIND spacecraft data. The geomagnetic activity is inferred from the SuperMAG project data. SuperMAG is a large chain which employs more than 300 ground stations to compute enhanced versions of the traditional geomagnetic indices. The SuperMAG auroral electroject SME index, an enhanced version of the traditional AE index, is used as an auroral power (AP) indicator. AP intensity jumps triggered by shock impacts are correlated with both shock speed and impact angle. It is found that high AP intensity events typically occur when high speed IP shocks impact the Earths magnetosphere with the shock normal almost parallel to the Sun-Earth line. This result suggests that symmetric and strong magnetospheric compression leads to favorable conditions for intense auroral power release, as shown previously by simulations and observations. Some potential mechanisms will be discussed.