HEAT-FLUX AND THERMAL CONDUCTION IN O-VHF RADAR OBSERVATIONS IN THE HIGH-LATITUDE TOPSIDE IONOSPHERE( AND H+ ION FLOWS DEDUCED FROM EISCAT)

With two periods of EISCAT-VHF radar observations, magnetically quiet and moderately disturbed, we have calculated the H+ and O+ heat fluxes in using formulae of Wu and Taieb (1993), accounting not only for tem perature gradients but also for pressure gradients, velocity gradients , and diffusion-thermal effects. They correspond to different physical processes that are calculated and compared between them. Then, the ge neral features of the H+ and O+ ion thermal conductions are studied du ring the two periods of observation in the high-latitude topside ionos phere. The analysis of the two periods of measurements revealed the fo llowing trends, to be confirmed by further observations: (1) During th e two periods the H+ heat flux Q2 is always upward in the altitude ran ge from 600 km up to about 1000 km. It is larger during the quiet peri od than during the disturbed period. (2) The most important dominant m echanism for H+ heat flux is the diffusion-thermal effect due to the H +-O+ collision, with a correcting term due to the H+ temperature gradi ent. (3) The O+ heat flux is always downward in the same altitude rang e during the two periods of observations. The absolute value during th e disturbed period is slightly larger than that during the quiet perio d. (4) The dominant mechanism for O+ heat flux is its temperature grad ient, corrected by the coupling with the H+ ion. (5) The O+ thermal co nduction is less important during the quiet period than during the dis turbed period, while for the H+ thermal conduction it is the contrary. (6) The H+ thermal conduction increases with altitude below about 100 0 km.