Intercomparison of NEAR and Wind interplanetary coronal mass ejection observations

Nearly 4 months of continuous interplanetary magnetic field measurements September 1997 through December 1997 have allowed us to compare four interplanetary coronal mass ejection (ICME) events seen by the NEAR and Wind spacecraft. When the spacecraft are in close proximity (separated by 1 degrees in azimuth relative to the sun) the ICMEs seen by Wind and NEAR have similar signatures as expected for structures with dimensions along the solar wind flow of similar to 0.2 AU. When the NEAR spacecraft is separated by similar to 5.4 degrees in azimuth from the Earth the vector signature of ICMEs seen at NEAR begins to differ from those seen at Wind even though the magnitude of the field in the events and the background solar wind show similarities at the two spacecraft. When the spacecraft are separated by 11.3 degrees the magnetic signatures are quite different and sometimes ICMEs are seen only at one of the two locations. Nevertheless, in all cases the magnetic helicity of the cloud structures seen at NEAR is the same as at Wind. The radial speeds of the shock and ICME leading edge as they cross Wind and the time delays of those events, for which we have some assurance that they also arrived at NEAR, indicate that the ICMEs decelerate measurably as they travel near 1 AU.