Interplanetary magnetic clouds: sources, properties, modeling, and geomagnetic relationship

R. P. Lepping and D. Berdichevsky

Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771


We present a review of interplanetary magnetic clouds, whose structures are usually those of very large magnetic flux ropes (of ~ 1/4 AU diameter at 1 AU) possessing intense axial magnetic fields and relatively cool internal proton plasma. The review covers the clouds’ solar sources, their average solar wind characteristics (based primarily on IMP-8, ISEE 3, and WIND spacecraft data), their interactions with the Earth’s magnetosphere, and their tendency (about ½ the time) to drive interplanetary shock waves and under what conditions. The clouds are analyzed according to a force free, cylindrically symmetric, flux rope model, which provides fundamental cloud properties, such as cross-sectional size, axial attitude, axial field intensity, and field handedness, as well as the spacecraft’s closest approach distance, and a quantitative means of evaluating the "quality" of the model’s fit to field data. All of these and other relevant quantities are reviewed statistically for many clouds from both the active and quiet parts of the solar cycle and the results compared. A natural by-product of cloud modeling is the ability to estimate the axial magnetic flux carried by the cloud. Such an estimate can be compared to an estimate of the solar source flux for a candidate region on the Sun for a check of flux consistency and a confirmation of the specific cloud-source relationship. Using a carefully chosen subset of WIND magnetic clouds, a profile of a generic cloud in terms of scalar quantities (field intensity, density, speed, proton thermal speed, and proton plasma beta) is produced and discussed. One of the most dramatic consequences of magnetic clouds arises from their interaction with Earth’s magnetosphere, since there is a high probability of this coupling causing geomagnetic storms, one of the elements of space weather.

in Magnetics, Signpost, submitted, 2000