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

We present preliminary results from a systematic study using simultaneous data from three spacecraft, Wind, IMP 8 and Geotail to examine interplanetary length scales and their implications on predictability for magnetic field parcels in the typical solar wind. Time periods were selected when the plane formed by the three spacecraft included the GSE x-direction so that if the parcel fronts were strictly planar, the two adjacent spacecraft pairs would determine the same phase front angles. After correcting for the motion of the Earth relative to the interplanetary medium and deviations in the solar wind flow from radial, we used differences in the measured front angle between the two spacecraft pairs to determine structure radius of curvature. Results indicate that the typical radius of curvature for these IMF parcels is of the order of 100 R_E. This implies that there are two important IMF scale lengths relevant to predictability: (1) the well-established scale length over which correlations observed by two spacecraft decay along a given IMF parcel, of the order of a few tens of Earth radii and (2) the scale length over which two spacecraft are unlikely to even observe the same parcel because of its curvature, of the order of a hundred Earth radii.

To appear in International Journal of Geomagnetism and Aeronomy, 2000