Magnetic structures inside boundary layers of magnetic clouds

Abstract

We analyze 23 magnetic cloud boundary layers (BLs) in Feb. 1995–Oct. 1998 and find that: (1) the distribution functions of fluctuations in the southward field component inside the boundary layer, ΔBzL, is very different from ΔBzS in the background solar wind and ΔBzM inside the cloud, with the enhancement in the fluctuation amplitude and the variation of the magnitude and direction of the average field. (2) in the maximum variance plane (MVP) composed of the maximum and medium variance directions, the walk of the tips of the magnetic field vectors in the BL could be classified into two types based on: (a) field vectors vibrate along a circle arc, which is possibly related with Alfven fluctuations inside the BL; (b) field vectors walk randomly in the MVP, which could be correlated with the turbulence inside the BL. (3) In the ϕ‐θ plane, fields inside the BL exhibits a ‘U’ or inverse ‘U’ shape with a spacing of about 180 degree in the azimuthal angle, which indicate the existence of a field reverse region and are often associated with the Alfvenic fluctuations. The results above suggest that the cloud's BL owns the magnetic structure different from that in the solar wind and cloud body, which is a manifestation for the interaction of the magnetic cloud (MC) with the solar wind (SW).