Responses of field-aligned currents and equatorial electrojet to sudden decrease of solar wind dynamic pressure during the March 2023 geomagnetic storm

We present a study of the magnetosphere-ionosphere coupling during the 23 March 2023 magnetic storm, focusing on the effect of the drastic decrease of the solar wind dynamic pressure occurred during the main phase. Our observations show that the negative pressure pulse had significant impact to the magnetosphere-ionosphere system. It weakened large-scale field-aligned currents and paused the progression of the storm main phase for ~3 hrs. Due to the sudden decrease of the plasma convection after the negative pressure pulse, the low-latitude ionosphere was over-shielded and experienced a brief period of westward penetration electric field, which reversed the direction of the equatorial electrojet. The counter electrojet was observed both in space and on the ground. A transient, localized enhancement of downward field-aligned current was observed near dawn, consistent with the mechanism for transmitting MHD disturbances from magnetosphere to the ionosphere after the negative pressure pulse.