Consequences of geomagnetic history on the high-latitude thermosphere and ionosphere: Averages

The thermospheric effects of "geomagnetic history" and the resulting ion-ne utral interactions are determined through the analysis of a long-term datab ase of high latitude neutral winds from Kiruna, Sweden, and simulations wit h the coupled thermosphere ionosphere plasmasphere model (CTIP). Three type s of geomagnetic history are examined in detail with the data and the model : steady state conditions in which the Kp index for the current three hours is the same as the Kp index for the previous 3 hours; previously quiet con ditions in which the Kp index for the current 3 hours is greater than the K p index for the previous 3 hours; and previously active conditions in which the Kp index for the current 3 hours is less than the Kp index for the pre vious 3 hours. It is shown that during the hours of darkness at Kiruna, whi le the ionosphere responds immediately to changes in activity, the neutral gas can take between 3 and 6 hours to recover from the effects of any previ ous activity. Model simulations show that the rate of energy dissipation is also significantly dependent on geomagnetic history. For the previously ac tive case the Joule heating and mechanical energy transfer rate are up to 4 times larger at certain latitudes as the steady state case. For the previo usly quiet case the heating rates are much smaller than the steady state ca se. There is a frequently made assumption that at high latitudes the mechan ical energy transfer rate may be ignored as insignificant compared with the Joule heating rate. The results presented here show that this assumption i s unreliable, particularly in the dusk sector and polar cap.