Ionospheric heating beneath the magnetospheric cleft

An analysis of 60,000 Alouette 1 electron density profiles has given values for the mean plasma temperature at heights of 400--1000 km for latitudes from 70 degreeS to 85 degreeN. Most results are for winter day conditions in the northern hemisphere; these show a well-defined peak beneath the magnetospheric cleft at a geomagnetic latitude of about 77degree. The temperature increase is typically 20% at a height of 400 km and 50% at a height of 1000 km. The increase in vertical temperature gradient shows that heat is flowing down from great heights. Large temperatures are observed from about 0800 to 1600 LT, with some increase from 0600 to 1800 hours. Heating is largely confined to a range of about 2degree in latitude. The position of the peak varies with magnetic activity, overall mean results giving a geomagnetic latitude (at 400 km) of 80-2Kp deg. Individual large magnetic storms show a similar response, with the temperature peak moving rapidly to 64degree latitude at Kp=8. During large storms the magnitude of the temperature increase is approximately doubled, and heating occurs over an area about 3 times larger than that for quiet conditions