Equatorial Electrojet (EEJ) Response to Interplanetary (IP) Shocks

Interplanetary (IP) shocks are known to cause significant modifications in Earth's magnetospheric and ionospheric current systems. The sudden enhancement of solar wind dynamic pressure (PDyn) associated with IP shocks could induce convection electric fields at high-latitude ionosphere which can promptly penetrate to equatorial and low-latitude regions. Additionally, prompt penetration electric field disturbances may also be induced due to the sudden southward/northward turnings of the Interplanetary Magnetic Field (IMF Bz) (eastward/westward turnings of the interplanetary electric field, IEFy) during IP shocks. The resultant electric field disturbances can significantly alter the ionospheric electrodynamics and equatorial electrojet (EEJ). In this study, the EEJ response to a large number of IP shocks that occurred during 2001-2021 has been investigated. The magnitude of the EEJ response to IP shocks shows a clear local time dependence and varies linearly with the change in solar wind dynamic pressure. The EEJ response is also found to depend considerably on the solar activity (F10.7 solar flux) and the polarity changes in IMF Bz associated with IP shocks. For the first time, an empirical relation is derived that can quantitatively estimate the EEJ response to IP shocks using a large number (306) of events that occurred over a span of two solar cycles. The derived empirical relation is found to be very accurate in predicting the response of the EEJ and exhibits an excellent correlation with observations. The eruptions and the energetic events on the Sun often release fast streams of charged particles (known as solar wind) at supersonic velocities into the interplanetary space. The arrival and impingement of these fast and dense solar wind structures on the Earth's magnetosphere cause highly dynamic changes in the currents flowing in Earth's Magnetosphere and Ionosphere. These changes will result in sudden changes in the Earth's magnetic (geomagnetic) field which can have potential impacts on the electric power grids, long-distance oil/gas pipelines and transmission lines, etc. Although these effects are more prominently known to occur at high latitude regions, the large and sharp disturbances in the geomagnetic field are also known to occur at equatorial latitudes due to the presence of an ionospheric current system known as the Equatorial Electrojet (EEJ). This study provides new insights into the important factors that control the variations in EEJ and derives an empirical relation to quantitatively predict the change in EEJ during the arrival of such fast and dense solar wind shock structures. The EEJ responds promptly to the arrival of IP shocks with sharp enhancement/decrease on the day/night timesThe magnitude of EEJ changes in response to IP shocks vary significantly with local time and depend strongly on solar wind dynamic pressureAn empirical relation is derived that can accurately predict the quantitative change in the EEJ in terms of local time and shock parameters