On the cause of IMF By related mid- and low latitude magnetic disturbances

An analysis of the effect of the IMF By on near-Earth low and mid-latitude magnetic disturbances is presented. In particular the contribution from field-aligned currents ( FACs) connected to the polar regions is investigated. Based on statistically determined high-latitude FAC patterns for various Interplanetary Magnetic Field ( IMF) directions, we estimate the FAC contribution to the mid-and low latitude magnetic disturbance and its dependence on the IMF. The estimated perturbations are compared with observations from the ground and from the low-altitude polar orbiting satellite Oersted. It is found that the long-distance effect of the high-latitude FACs constitute the major source to IMF By and B-z related magnetic east-west disturbances at mid-and low latitudes.