Short-period features of the interplanetary plasma and their evolution

The solar wind plasma exhibits many features of the solar surface passed on to the interplanetary medium as temporal variations due to the solar rotat ion. The yearly average values of solar wind velocity, and geomagnetic inde x A(p) during 1965-1999 were found to exhibit long period evolution. They w ere found to peak around the declining phase of each solar cycle. While the solar wind velocity peaks around the second half of the declining phase, t he IMF field strength increases around the first half of the declining phas e of each solar cycle. The power spectrum of these parameters shows peaks a round 37-day, 30-day, 27-day, 13.5-day, 9-day, and 7-day periods. The tempo ral evolution of the power spectrum of the solar wind plasma parameters and the geomagnetic activity index A(p) are also studied in detail and present ed with the help of contour graphs. These studies indicate that the strengt h of the quasi-periodicities in the interplanetary medium evolves with time .