Comparison of Field‐Aligned Current Responses to HSS/SIR, Sheath, and Magnetic Cloud Driven Geomagnetic Storms

The time delay from an interplanetary driver arriving at the magnetopause to the response in the ionosphere has never been quantified separately for different types of storm drivers. This study investigates the delay for storms driven by high‐speed streams and associated stream interaction regions (HSS/SIR), or by interplanetary coronal mass ejection sheaths and magnetic clouds (MC). The total field‐aligned current (FAC) and SME index lag the Newell coupling function (NCF) by 40 ± 10 min during storms driven by HSS/SIR and sheaths, and by 60 ± 10 min for MCs. The correlation coefficient between FAC and NCF reaches maximum value as NCF is averaged over the preceding 80 min for sheath, 90 min for HSS/SIR, and 140 min for MC storms. Plain Language Summary The Sun causes perturbations in the solar wind, which may drive geomagnetic storms associated with strong field‐aligned currents to the ionosphere. The solar wind drivers studied in this paper are high‐speed stream/stream interaction regions (HSS/SIR), and sheath and magnetic cloud (MC) interplanetary coronal mass ejections. The exact time from the arrival of the solar wind interplanetary driver at the magnetopause to the response in the ionospheric and field‐aligned currents (FAC) have not been quantified for different types of solar wind drivers. We study this time delay during geomagnetic storms and find that it is typically 40 min for HSS/SIR‐ and sheath‐driven storms, and 60 min for MC‐driven storms. Additionally, the total FAC best correlate with the solar wind averaged over the preceding 80 min for sheath, 90 min for HSS/SIR, and 140 min for MC‐driven storms. These results may help improve the accuracy of forecasting solar wind disturbances on the high‐latitude ionosphere. Key Points Correlation between Newell coupling function (NCF) and total field‐aligned current (FAC) is studied for different storm drivers Best correlation for sheath, high‐speed stream, and magnetic cloud storms is found by integrating NCF over 80, 90, and 140 min, respectively Sheath‐driven storms are associated with the highest values of total FAC and NCF