Explicit IMF B -Dependence of Energetic Protons and the Ring Current

The most important parameter driving the solar wind-magnetosphere interaction is the southward (B ) component of the interplanetary magnetic field (IMF). While the dawn-dusk (B ) component of the IMF is also known to play an important role, its effects are usually assumed to be independent of its sign. Here we demonstrate for the first time a seasonally varying, explicit IMF B -dependence of the ring current and Dst index. Using satellite observations and a global magnetohydrodynamic model coupled with a ring current model, we show that for a fixed level of solar wind driving the flux of energetic magnetospheric protons and the growth-rate of the ring current are greater for B  < 0 (B  > 0) than for B  > 0 (B  < 0) in Northern Hemisphere summer (winter). While the physical mechanism of this explicit B -effect is not yet fully understood, our results suggest that IMF B modulates magnetospheric convection and plasma transport in the inner magnetosphere.