Magnetic cloud field intensities and solar wind velocities

Abstract

For the sets of magnetic clouds studied in this work we have shown the existence of a relationship between their peak magnetic field strength and peak velocity values, with a clear tendency that clouds which move at higher speeds also possess higher core magnetic field strengths. This result suggests a possible intrinsic property of magnetic clouds and also implies a geophysical consequence. The relatively low field strengths at low velocities is presumably the cause of the lack of intense storms during low speed ejecta. There is also an indication that this type of behavior is peculiar for magnetic clouds, whereas other types of non cloud-driver gas events do not seem to show a similar relationship, at least for the data studied in this paper. We suggest that a field/speed relationship for magnetic clouds, as that obtained in our present study, could be associated with the cloud release and acceleration mechanism at the sun.

Since for magnetic clouds the total field tyically has a substantial southward component, Bs, our results imply that the interplanetary dawn-dusk electric field, given by v×Bs (where v is the cloud's velocity), is enhanced by both factors. Therefore, the consequent magnetospheric energization (that is governed by this electric field) becomes more efficient for the occurrence of magnetic storms.