  We utilize solar rotation average geomagnetic index ap and various solar wind
plasma and field parameters for four solar cycles 20-23. We perform analysis to
search for a best possible coupling function at 27-day time resolution.
Regression analysis using these data at different phases of solar activity
(increasing including maximum/decreasing including minimum) led us to suggest
that the time variation of interplanetary electric potential is a better
coupling function for solar wind-magnetosphere coupling. We suspect that a
faster rate of change in interplanetary electric potential at the magnetopause
might enhance the reconnection rate and energy transfer from the solar wind
into the magnetosphere. The possible mechanism that involves the interplanetary
potential fluctuations in influencing the solar wind-magnetosphere coupling is
being investigated.
