Influence of interplanetary magnetic field and plasma on geomagnetic activity during quiet-sun conditions

Abstract

Observations by the IMP-1 satellite of the interplanetary magnetic field and plasma were compared with the three-hour geomagnetic activity index Kp. The average Kp is approximately a linear function of the interplanetary field magnitude B in gammas (Average Kp = (0.33 plus or minus 0.02) B plus or minus 0.2). It appears significant that this relation between Average Kp and field magnitude passes through the origin, whereas the linear relation between Average Kp and solar wind velocity does not. The average Kp is approximately a linear function of solar wind velocity, but with perhaps a slightly different slope and zero-intercept from the similar relation observed by Snyder, Neugebauer and Rao with Mariner 2. Little correlation is observed between Average Kp and solar wind density, but this result is consistent with the interplanetary sector pattern discussed by Wilcox and Ness. Cross-correlation as a function of time lag of Kp and interplanetary field (or solar wind velocity) yields a positive peak correlation at zero lag, suggesting that a large part of the response of the magnetosphere to solar wind excitation occurs within the three-hour Kp period. (Author)