  Solar wind-magnetosphere coupling, its causes and consequences have been
studied for the last several decades. However, the assessment of continuously
changing behaviour of the sun, plasma and field flows in the interplanetary
space and their influence on geomagnetic activity is still a subject of intense
research. Search for the best possible coupling function is also important for
space weather prediction. We utilize four geomagnetic indices (ap, aa, AE and
Dst) as parameters of geomagnetic activity level in the earth's magnetosphere.
In addition to these indices, we utilize various solar wind plasma and field
parameters for the corresponding periods. We analyse the geomagnetic activity
and plasma/field parameters at yearly, half-yearly, 27-day, daily, 3-hourly,
and hourly time resolutions. Regression analysis using geomagnetic and solar
wind data of different time resolutions, over a continuous long period, and at
different phases of solar activity (increasing including maximum/decreasing
including minimum) led us to suggest that two parameters BV/1000 (mV/m) and BV2
(mV/s) are highly correlated with the all four geomagnetic activity indices not
only at any particular time scale but at different time scales. It probably
suggests for some role of the fluctuations/variations in interplanetary
electric potential, its spacial variation [i.e., interplanetary electric field
BV (mV/m)] and/or time variation [BV2 (mV/s)], in influencing the reconnection
rate.
