Effect of ICME‐Driven Storms on Field‐Aligned and Ionospheric Currents From AMPERE and SuperMAG

Abstract

This study investigates the field‐aligned currents (FACs) and ionospheric equivalent currents for interplanetary coronal mass ejection (ICME)‐driven storms by considering 45 events with a minimum Dst ≤ −50 nT. The FACs and ionospheric equivalent currents are studied by applying a superposed epoch analysis to data from AMPERE and SuperMAG with the zero epoch (t0) centered at the onset of the storm main phase. The currents and number of substorm onsets begin to increase 3 hr before t0 and maximizes about 1 hr after t0. The currents and number of substorm onsets remain high throughout the entire storm main phase, until at t0 + 14 hr they start to slowly relax back to quiet time conditions. The storms were separated into two groups based on the solar wind dynamic pressure pdyn around t0. High pdyn storms are mostly driven by the sheath region ahead of the ejecta. These storms have short main phase durations and larger currents early in the main phase which maximize at t0 + 50 min. The low pdyn group contains storms that start during the magnetic clouds (MC) and have gradually increasing currents that maximize at t0 + 11 hr, close to the end of the storm main phase. For the first 4 hr of the storm main phase, the currents in sheath‐driven storms are larger than for MC‐driven storms. The Russell‐McPherron effect is less important for ICME‐driven storms where only 44% have a contribution, compared to 82% of high speed stream/stream interaction driven storms.

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

“…(2021) and Pedersen et al. (2022) where the unshifted and superposed solar wind coupling functions have higher CCs with FAC and AE index for ICME‐driven storms compared to HSS/SIR‐driven storms. The cross‐correlation peak between the NCF and FAC is sharpest for HSS/SIR storms and flatter for sheath and MC storms, which is likely to be due to the driver, since the auto‐correlation for the NCF behaved in the same manner in Figure 1 for the different storms.…”

“…The low R 2 values between the 10-min SYM-H index and FAC values shown in Figure 4 are in line with earlier observations. Pedersen et al (2021Pedersen et al ( , 2022 show that the largest FAC occurs early in the storm main phase for HSS/SIR and sheath storms, and a few hours before SYM-H minimum for MC storms.…”

“…A list of the storms included in this study is in the Supporting Information S1 (28 HSS/SIR, 26 sheath, and 19 MC). The same storms were studied by Pedersen et al (2021Pedersen et al ( , 2022.…”

“…Our previous studies have characterized the typical evolution of FACs, ionospheric equivalent currents, and substorms during high‐speed stream/stream interaction region (HSS/SIR) driven storms, as well as storms driven by sheath and magnetic cloud (MC) regions of interplanetary coronal mass ejections (ICME) (Pedersen et al., 2021, 2022). In this paper, we analyze the time delay between the interplanetary driver at the magnetopause and the FACs, ionospheric currents, as well as several geomagnetic indices for the three types of storm drivers using cross‐correlation analysis.…”

The Occurrence of Embedded Region 1 and 2 Currents Depends on Geomagnetic Activity Level

“…The examples show that the IMF can be either southward or northward at the time of the embedded FACs. This is expected because solar wind parameters such as the IMF are not instantly related to the M‐I configuration; their impacts to the M‐I FAC system can be delayed by hours (e.g., Pedersen et al., 2022). We thus focus on parameters that can instantly reflect the state of the M‐I system—the Kp, AL, and Dst indices, which are known to be correlated with FAC properties in the auroral zone (e.g., Le et al., 2010).…”