IONOSPHERIC ELECTRON HEATING BY STRUCTURED ELECTRIC-FIELDS - THEORY AND EXPERIMENT

Ionospheric electron heating due to structured electric fields is cons idered herein. In a survey of incoherent scatter (IS) radar data gathe red with the Sondrestrom IS radar in Greenland (66.99 degrees N, 50.95 degrees W), we find that such heating takes place at F layer altitude s accompanying intense auroral events in the E layer. Because of compe tition with heating by precipitating particles this type of heated reg ion can only be observed when it is shifted from the geomagnetic field line penetrating the associated E layer are. We have detected regions of this sort in which we argue that the temperature is enhanced eithe r by illumination of auroral ionospheric cavities by an Alfven wave so urce or by collocation with turbulent electrostatic fields. We have de veloped a model that predicts the observed T-e enhancement in the F la yer. We also present a consistent physical picture of auroral activity involving coupling between the magnetosphere and the ionosphere via e lectrostatic and wave- or turbulence-induced field-aligned currents. B oth can be generated by the region surrounding the electron accelerati on zone. Applying our model to the observations allows us to separate electron heating due to structured fields (with a pronounced maximum i n the F layer), static field-aligned currents (with the electron tempe rature smoothly increasing with altitude from the F layer up to the ma gnetosphere), and electron impact in the E layer. In turn, the tempera ture observations give us information on the Alfven wave impinging on the auroral F layer and/or the turbulent electrostatic fields which ma p to the ionosphere.