Dipole tilt angle effects on the latitude of the cusp and cleft/low‐latitude boundary layer

Abstract

A large data set of approximately 12,000 Defense Meteorological Satellite Program satellite F7 crossings of the cusp or the cleft (i.e., the dayside magnetospheric boundary layer) over a 3‐year period is studied for seasonal dependence in latitudinal position. A carefully tested algorithm is used to distinguish the various dayside particle precipitation regions and boundaries. It is found that in the 1100–1300 MLT sector, the cusp proper exhibits about −0.06° magnetic latitude (MLAT) shift for each degree increase in dipole tilt angle. Thus the difference between the average summer and winter cusp positions is close to 4° MLAT, approximately symmetric about equinox. For the cleft (magnetospheric boundary layer) the variation is smaller. For example, in the 0700–0900 MLT sector the cleft equatorward boundary shift is −0.027° MLAT/1° dipole tilt. These results are in general agreement with the predictions of empirical magnetospheric magnetic field models. Various ground‐based and low‐altitude observations can be systematically affected by the seasonal latitudinal shift herein documented.