The average tangential electric field at the noon magnetopause

Two hundred and five magnetopause passes of the ISEE 1 satellite through the magnetopause within 2 hrs of local noon during the time period 1977-1981 were examined in order to determine the relationship between the dawn-dusk tangential electric field at the magnetopause and the northward component of the magnetosheath magnetic field; the ratio of these quantities yields the speed of the plasma flow toward the magnetopause (i.e., the reconnection flow speed). The results indicate that, on the average, reconnection occurs at the subsolar magnetopause, and that the average reconnection flow speed of magnetosheath plasma toward the magnetopause is about 15 percent of the local Alfven speed.