Dynamics and solar wind control of the recovery of strong geomagnetic storms

In this work we have studied about the characteristics and dynamical changes during the recovery time of moderate and strong geomagnetic storms of (\(\mathrm{Dst}<-50\text{ nT}\)). In our investigation of 57 storms triggered by CMEs/CIRs, we concentrated on the solar wind’s influence on their decay phases. Selected storms were classified into distinct groups based on their recovery characteristics. Employing the superposed epoch analysis and best fit methods, we scrutinized several interplanetary solar wind plasma and field parameters and their various functions. The analysis encompassed various single, dual, and multiple interplanetary plasma and field parameters/functions. We determined the most representative characteristic time for the storm’s recovery profile by carefully fitting an exponential curve. A correlation analysis between Dst and solar wind parameters/functions led us to isolate a coupling function (\(\rho ^{\frac{1}{2}}\mathrm{Ey}\)) which best described the decay rate of the ring current. It shows that electric field term (Ey) coupled with a viscus term (\(\rho ^{\frac{1}{2}}\)) plays pivotal role in determining the recovery rate of a geomagnetic storms. Additionally, we modeled the complex patterns of Dst recovery in relation to solar wind parameters and functions using a second-order polynomial. Remarkably, during the recovery phase, a dynamic correlation between Dst and solar wind parameters/functions was revealed. The three-parameter solar wind-magnetosphere electrodynamical coupling functions, which combines the viscus term (\(\rho ^{\frac{1}{2}}\)) and the electric field-related function (\(\mathrm{v}^{\frac{4}{3}}\mathrm{B}\)) (\(\rho ^{\frac{1}{2}}\mathrm{v}^{\frac{4}{3}}\mathrm{B}\)), significantly impacts the recovery phase of geomagnetic disturbances. Our investigation extended to the relationship between main and recovery phase durations, providing valuable insights into the solar wind’s intricate control over the decay of the geomagnetic disturbances. These findings contribute significantly to advancing our comprehension of the complex relationship between solar wind dynamics and the evolution of geomagnetic disturbances.