MAGNETIC CLOUD FIELD INTENSITIES AND SOLAR-WIND VELOCITIES

For the sets of magnetic clouds studied in this work we have shown the existence of a relationship between their peak magnetic field strengt h and peak velocity values, with a clear tendency that clouds which mo ve 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 in tense 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 rel ationship, at least for the data studied in this paper. We suggest tha t a field/speed relationship for magnetic clouds, as that obtained in our present study, could be associated with the cloud release and acce leration mechanism at the sun. Since for magnetic clouds the total fie ld tyically has a substantial southward component, B-s, our results im ply that the interplanetary dawn-dusk electric field, given by v x B-s (where v is the cloud's velocity), is enhanced by both factors. There fore, the consequent magnetospheric energization (that, is governed by this electric field) becomes more efficient for the occurrence of mag netic storms.