Minimum variance analysis for 2D structures using two satellites

Many structures in the solar wind are not ideal one dimensional, but two or three dimensional. We present a method to determine the orientation and the propagation velocity of a 2D structure in a satellite frame using two satellites under the assumption that a reference frame exists in which no temporal variations occur und that the magnetic field is divergence-free. The magnetic field is linearly extrapolated from one satellite to an auxilary point and is compared with the measured field from the other satellite. Also a simplification of the method for Alfvenic structures is given. The distance between the satellites determines the scale of the structure. On the time scale of 10 h, using WIND and IMP 8 data, no clear 2D structures are observable. Further investigations on smaller scales could be done with CLUSTER II.