Time Sequence of Magnetospheric Responses to a Southward IMF Turning

We use MHD simulations to study the time sequence of magnetospheric responses to a synthetic event with a southward interplanetary magnetic field (IMF) turning. The onset of dayside magnetopause reconnection launches a weak rarefaction wave and sunward flow in the equatorial magnetosphere simultaneously with a tailward flow through the polar cap. This convection results in the accumulation of magnetic flux in the tail lobes and thinning of the tail current layer which provides favorable conditions for the onset of nightside reconnection. The onset of nightside reconnection about 40 min later closes the Dungey convection cycle, resulting in a second increase in the sunward flow in the equatorial plane. Variations of the magnetopause standoff distance as well as the size of the polar cap (PC) may indicate the onsets of the dayside and nightside reconnections. We compare the results of two MHD models and discuss their differences. Plain Language Summary The auroras and other space weather phenomena are produced by the interaction of the solar wind with the Earth's magnetic environment. The fundamental plasma process of magnetic reconnection modulates this interaction, which then drives a circulation of magnetic field and plasma within the magnetosphere known as the Dungey cycle. Reconnection occurs when the magnetic field in the solar wind points southwards but turns off when it is northwards. The sequence of events within the magnetosphere in response to a southwards turning of the magnetic field is currently poorly understood. In this study, we model the interaction with two magnetohydrodynamic simulation codes. These show a rarefaction wave from the front of the magnetosphere toward the magnetotail in response to the turn‐on of reconnection. Thereafter magnetic reconnection occurs in the magnetotail to complete the cycle. Although the simulations differ in the details, the two agree on this sequence of events, providing new insights into the dynamics of the magnetosphere. Key Points We investigate magnetospheric convection after southward turning and highlight the differences between the two MHD models Two‐step response in convection after dayside and nightside reconnection Variations in the magnetopause standoff distance may indicate variations in the magnetic flux