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

The most important parameter driving the solar wind-magnetosphere interaction is the southward (B z ) component of the interplanetary magnetic field (IMF). While the dawn-dusk (B y ) 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 y -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 y  < 0 (B y  > 0) than for B y  > 0 (B y  < 0) in Northern Hemisphere summer (winter). While the physical mechanism of this explicit B y -effect is not yet fully understood, our results suggest that IMF B y modulates magnetospheric convection and plasma transport in the inner magnetosphere.

Soft X-ray and ENA Imaging of the Earth's Dayside Magnetosphere.

The LEXI and SMILE missions will provide soft X-ray images of the Earth's magnetosheath and cusps after their anticipated launch in 2023 and 2024, respectively. The IBEX mission showed the potential of an Energetic Neutral Atom (ENA) instrument to image dayside magnetosheath and cusps, albeit over the long hours required to raster an image with a single pixel imager. Thus, it is timely to discuss the two imaging techniques and relevant science topics. We simulate soft X-ray and low-ENA images that might be observed by a virtual spacecraft during two interesting solar wind scenarios: a southward turning of the interplanetary magnetic field and a sudden enhancement of the solar wind dynamic pressure. We employ the OpenGGCM global magnetohydrodynamics model and a simple exospheric neutral density model for these calculations. Both the magnetosheath and the cusps generate strong soft X-rays and ENA signals that can be used to extract the locations and motions of the bow shock and magnetopause. Magnetopause erosion corresponds closely to the enhancement of dayside reconnection rate obtained from the OpenGGCM model, indicating that images can be used to understand global-scale magnetopause reconnection. When dayside imagers are installed with high-ENA inner-magnetosphere and FUV/UV aurora imagers, we can trace the solar wind energy flow from the bow shock to the magnetosphere and then to the ionosphere in a self-standing manner without relying upon other observatories. Soft X-ray and/or ENA imagers can also unveil the dayside exosphere density structure and its response to space weather.