Global Three‐Dimensional Simulation of the Earth's Magnetospheric and Ionospheric Responses to Small‐Scale Magnetic Flux Ropes in the Solar Wind

The orientation of magnetic flux ropes in the solar wind is an important component that affects interactions with the Earth's magnetosphere and ionosphere. In this study, we performed global magnetohydrodynamic (MHD) simulations on the responses of the magnetosphere and ionosphere to the impact of small-scale magnetic flux ropes (SMFRs). We considered four types of SMFR structures according to the alignment direction of the flux rope axis in the plane perpendicular to the Sun-Earth line. The flux rope axis of the two types is oriented in the north-south direction, while the flux rope axis of the other two types is oriented along the dusk-dawn direction. Accordingly, the B-y and B-z profiles of the SMFR types vary as the SMFR passes through the Earth. The main features of the response are as follows: (i) The magnetic reconnection on both the dayside and nightside is well organized by the specific profiles of B-y and B-z. (ii) One type of SMFRs where B-z turns from south to north and B-y remains duskward leads to plasmoid formation in the tail, distinguishing it from the other types. (iii) The temporal responses of the tail plasma flow, cross-tail electric field, tail plasma pressure, and cross-polar cap potential depend on the specific profiles of B-y and B-z, causing different response times. (iv) The evolution of ionospheric convection pattern sensitively depends on the magnetic field variation within SMFRs. (v) The peak value of cross-polar cap potential ranges from 25 kV to > 50 kV, providing energy storage suitable for substorm expansion.