Abstract
Interplanetary coronal mass ejections (ICMEs) are among the main drivers of major geomagnetic storms. The recovery phase of such storms, characterized by a return of geomagnetic indices to pre-disturbance levels, is primarily governed by the decay of the ring current and the cessation of solar wind energy input. This study examines how the characteristics of the recovery phase, specifically the exponential decay time constant ( \(\tau \) ) of key geomagnetic indices, depend on the polarity configuration of the interplanetary magnetic field (IMF) of the ICMEs. A total of 163 ICME-driven storms from 1995 to 2015 were analyzed using hourly OMNI data. The recovery phase of each storm was modeled with an exponential decay to extract \(\tau \) for the Disturbance Storm Time (Dst) index, Planetary amplitude (ap) index, and Auroral Electrojet (AE) index. Events were categorized into eleven distinct IMF polarity and flux rope configurations to evaluate polarity-dependent recovery behavior. Correlation analyses were also conducted to assess the relationship between \(\tau \) of geomagnetic indices and various solar wind parameters, including IMF \({{B}_{z}}\) , solar wind speed, and coupling functions. Results reveal significant differences in recovery durations across ICME polarity groups. The SN polarity exhibited the fastest Dst recovery ( \(\tau = 18.68 \pm 0.80\) h), whereas SNS and \({{F}^{ + }}\) configurations exhibited the slowest recoveries ( \(\tau = 43.95 \pm 1.27\) and \(50.97 \pm 1.58\) h, respectively). For the ap and AE indices, the fastest recovery occurred in NSN ( \(\tau = 4.02 \pm 0.46\) h) and SNN ( \(\tau = 4.33 \pm 0.61\) h) configurations, while prolonged recovery was associated with \(Fr\) (ap) and NSS (AE) events ( \(\tau > 29.90\) h). Events dominated by northward magnetic fields recovered significantly faster than those with prolonged southward IMF orientations. Strong statistical coupling was found between \(\tau \) (Dst) and \(\tau \) (ap) ( \(r = 0.87\) ), while \(\tau \) (AE) was most sensitive to \(n{{E}_{y}}\) ( \(r = - 0.52\) ). Additionally, configurations with small rotation angles ( \({{F}^{ - }}\) ) recovered more rapidly than those with complex rotations ( \({{F}^{ + }}\) ), reflecting the role of magnetic structure in sustaining energy input. These findings enhance predictive models of magnetospheric recovery by linking IMF polarity and flux rope topology to the timescales of geomagnetic relaxation.
