Poker Flat Incoherent Scatter Radar observations of anomalous electron heating in the E region

A comprehensive 2-year dataset collected with the Poker Flat Incoherent Scatter Radar (PFISR) located near Fairbanks, Alaska (MLAT = 65.4 N) is employed to identify and analyse 22 events of anomalous electron heating (AEH) in the auroral E region. The overall AEH occurrence probability is conservatively estimated to be 0.3 % from nearlycontinuous observations of the E region by PFISR, although it increases to 0.7–0.9 % in the dawn and dusk sectors where all AEH events were observed. The AEH occurrence variation with MLT is broadly consistent with those of events with high convection velocity (> 1000 m s−1) or electron temperature (> 800 K), except for much smaller AEH probability and absence of AEH events near magnetic midnight. This suggests that high convection electric field by itself is necessary but not sufficient for measurable electron heating by two-stream plasma waves. The multi-point observations are utilised to investigate the fundamental dependence of the electron temperature on the convection electric field, focusing on the previously-proposed saturation effects at extreme electric fields. The AEH dataset was found to exhibit considerable scatter and, on average, similar rate of the electron temperature increase with the electric field up to 100 mV m−1 as compared with previous studies. At higher (highest) electric fields, the electron temperatures are below the linear trend on average (within uncertainty). By employing a simple fluid model of AEH, it is demonstrated that some of this deviation from the linear trend may be due to a stronger vibrational cooling at very large temperatures and electric fields.