The Magnitude of IMF By Influences the Magnetotail Response to Solar Wind Forcing

Abstract

The dynamics of substorms are known to be dominated by the North-South ((Formula presented.)) component of the Interplanetary Magnetic Field (IMF), which is the most important driver of the dayside reconnection. Even though the dawn-dusk ((Formula presented.)) component is also known to play a role in substorm dynamics, its effects are not yet fully understood. In this paper we study how IMF (Formula presented.) modulates the onset latitude, strength and occurrence frequency of substorms as well as the isotropic boundary (IB) latitude of energetic protons. We show that the substorm onset latitude and the IB latitude are about one degree lower for large magnitude (Formula presented.) ((Formula presented.) nT) than for small (Formula presented.). In contrast, the substorm occurrence frequency is larger for small (Formula presented.). We suggest that the magnetotail is more stable during large (Formula presented.), requiring the magnetotail lobes (and hence the polar cap) to contain more flux to initiate a substorm compared to the situation when (Formula presented.) is small.