Effects of Subauroral Polarization Streams on the Equatorial Electrojet During the Geomagnetic Storm on 1 June 2013: 2. The Temporal Variations

Using ground-based magnetic field measurements and numerical simulations from the Thermosphere-Ionosphere Electrodynamic General Circulation Model (TIEGCM), a first paper (Zhang, Yamazaki, et al., 2021, doi: https://doi.org/10.1029/2021JA029681; under review) introduced the potential roles of disturbance dynamo electric field due to subauroral polarization streams (SAPS) on the equatorial electrojet (EEJ) during a moderate geomagnetic storm on 1 June 2013. Our second study investigated the temporal responses of equatorial electrojet to SAPS. At noon, the residual EEJ (Delta EEJ) owing to SAPS flows westward, that is, counter equatorial electrojet (CEJ). The temporal variation of CEJ excited by the dynamo electric field was basically consistent with that by SAPS, and the effects of zonal wind were larger than those of meridional wind. The relative time delay of CEJ and SAPS was related to the propagation time of disturbance wind from mid-latitudes to low-latitudes. It took 2-3 hr for SAPS-related disturbance wind to propagate to the equatorial region and change the polarity of EEJ. The influence of meridional winds on the temporal variations of Delta EEJ is related to the generation of eastward currents at mid-latitudes, which can accumulate the positive charges at dusk terminator and then generate a westward electric field at lower latitudes. Plain Language Summary The equatorial electrojet (EEJ) represents a ribbon of intense electric current flowing in the ionospheric E region (approximately 110 km) on the dayside along the dip equator. Its behaviors are controlled by the daytime ionospheric electric field and ionospheric conductivity. However, the temporal variations of EEJ in response to the subauroral polarization streams (SAPS), an interesting and important physical phenomenon at subauroral latitudes, are seldom explored and poorly understood. The understanding of EEJ behaviors and their associated physical drivers during SAPS periods can contribute to the modeling and forecasting of the equatorial space environment, and the understanding of the coupling between ionosphere-thermosphere systems at high-latitudes and dip equator.

Automated summary

This study investigates the temporal responses of the equatorial electrojet (EEJ) to subauroral polarization streams (SAPS). The results show that the counter equatorial electrojet (CEJ) excited by SAPS exhibits consistent temporal variations with SAPS, with a larger influence from zonal wind than meridional wind. The relative time delay between CEJ and SAPS is related to the propagation time of disturbance wind. This study contributes to the understanding of EEJ behaviors during SAPS periods and their implications for modeling and forecasting the equatorial space environment.