Longitudinal Differences in the Response of Equatorial Electrojet to the Sudden Decrease of Solar Wind Dynamic Pressure.

The sudden decrease in solar wind dynamic pressure (PDyn) is a frequent phenomenon that has important influences on the equatorial ionosphere. Using 21 years of horizontal geomagnetic field measurements from three ground stations (Tatuoca, TTB, −48.5° Geographic longitude, GLon; Mbour, MBO, −16.96° GLon; Tirunelveli, TIR, 77.8° GLon), the longitudinal differences in the response of the equatorial electrojet (EEJ) to sudden drops in PDyn are explored in this work. The results reveal a significant reduction in the EEJ (ΔEEJ), suggesting the primary roles of the westward electric field caused by the sudden decrease in PDyn. The EEJ reaches its minimum within approximately 15–20 min. Significant longitudinal differences in ΔEEJ are observed, with the strongest response at TTB and the weakest at MBO. Interestingly, ionospheric conductivity, as indicated by the solar zenith angle and solar flux (F10.7), exhibits similar longitudinal patterns. This is identified as the primary factor explaining the longitudinal differences in ΔEEJ. Further diagnose shows that the magnitude of sudden changes in PDyn, the merging electric field (Em), or IMF Bz play a negligible role in the formation of longitudinal dependences of ΔEEJ. When IMF Bz shifts northward or southward during the sudden decrease in PDyn, the westward change in ΔEEJ current is either enhanced or suppressed accordingly. Plain Language Summary: In addition to the influence of interplanetary magnetic field (IMF), sudden changes in solar wind dynamic pressure (PDyn) also play a significant role in the Earth's ionosphere. Previous studies have demonstrated that sudden decreases in PDyn significantly affect the equatorial electrojet (EEJ). However, the longitudinal variations of these effects and the impact of different IMF Bz conditions on EEJ response remain poorly understood. This study uses several decades of ground‐based magnetic field observations to first reveal the longitudinal variations and differing responses of the EEJ to PDyn drops under various IMF Bz conditions. The underlying mechanisms of these responses are also investigated. Key Points: EEJ experiences a notable decrease and reaches its minimum roughly 15–20 min following a sudden drop in solar wind dynamic pressureThe longitudinal variations in the EEJ responses can be explained by the ionospheric conductivityThe northward or southward shift of IMF Bz can either enhance or suppress the EEJ's response to dynamic pressure drops [ABSTRACT FROM AUTHOR]