The Substorm Cycle at Mercury

The large-scale dynamic behavior of Mercury's highly compressed magnetosphere is primarily powered by magnetic reconnection between the solar wind and the planetary magnetic field. Reconnection transfers energy and momentum from the solar wind to the magnetosphere and drives the large-scale circulation of magnetic flux through the system, predominantly via the substorm cycle. We will present a statistical analysis of the average substorm amplitude, duration and frequency using magnetic field data acquired in orbit about Mercury by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft. We will also present an example of steady magnetospheric convection in Mercury's magnetosphere, during which reconnection is ongoing both at the dayside magnetopause and in the magnetotail, but large-scale magnetic energy storage and release is not observed. We aim to ascertain the combination of internal magnetospheric and external solar wind parameters that lead to a substorm, or a period of steady magnetospheric convection in Mercury's magnetosphere.