Interplanetary magnetic clouds at 1 AU

Statistical characteristics of magnetic clouds observed in the interplanetary medium near earth are investigated. Forty-five magnetic clouds are identified in which one component of B changes direction by rotating parallel to a plane, while the component of B normal to that plane is either constant or zero. Three classes of clouds are identified: clouds preceded by a shock, clouds followed by a stream interface, and clouds associated with a CME. In superposed epoch plots, the maximum field strength is found to be approximately the same for each class of clouds. Temperatures are all low, densities are somewhat high, and the pressure is higher that the ambient pressure in all three types of clouds. The physical characteristics of the magnetic clouds and their rate of occurrence suggests that many or all of the clouds may be related to coronal mass eject elements observed in white light data.