Journal Article

Dawn‐Side Anomaly in Sudden Geomagnetic Field Responses to Solar Wind Pressure Discontinuities During the 10 May and 10 October 2024 Geomagnetic Storms

Tulasi Ram, S, Parashar, Shivam, Remya, B, Chakrabarty, D, Raghav, Anil, Yadav, Vipin K, Oliveira, D. M, Dimri, A. P, Kumar, Abhishek, Rai, Deeksha, Nilam, B

2026

Overview

Interactions of solar wind dynamic pressure (SWDP) discontinuities with Earth's magnetosphere cause geomagnetic Sudden Commencements (SCs). Typically, positive/negative SCs occur at low latitudes due to enhancements/reductions in SWDP. However, anomalous dawn‐side SCs of opposite polarity were recently reported during the 10 May 2024, superstorm [Nilam et al., 2025, https://doi.org/10.1029/2025GL117032]. This study examines SC responses to positive and negative pressure discontinuities on the May 10 and October 10 storms under similar storm phases and local times. Both events consistently revealed anomalous dawn‐side low latitude SCs opposite to those at other longitudes. We suggest the main impulse of the Disturbance Polar (DP) field extending equatorward as the most likely source. Under highly compressed background magnetosphere conditions, field‐aligned currents associated with DP fields can shift to lower L‐shells, producing such anomalous SCs at dawn‐side low latitudes. These findings provide new insights into dawn‐side magnetosphere–ionosphere coupling during intense storms.

• Publisher: John Wiley & Sons, Inc
• Subject: Charged particles / Discontinuity / Dynamic pressure / Earth magnetosphere / Electric fields / Geomagnetic field / Geomagnetic storms / Geomagnetism / Ionosphere / Latitude / Magnetic fields / Magnetic storms / Magnetosphere-ionosphere coupling / Solar wind / Solar wind pressures / Storms / Sudden commencements / Wind pressure