Incoherent scatter radar observations of westward electric fields and plasma densities in the auroral ionosphere, 1

This paper reports the results of incoherent scatter radar observations of high-altitude ion drifts and other plasma parameters made February 24, 1972, at Chatanika, Alaska (L = 5.7), during a period of magnetic disturbance. For this experiment, conducted between 0909 to 1303 UT (2309 to 0303 AST), the radar line of sight was held fixed in the magnetic meridian plane so that the observed north-south ion drifts could be interpreted in terms of a westward electric field that ranged in magnitude from −10 to +35 mV m−1. The results confirm many effects found previously through other experimental techniques. Southward ion drifts predominated during the 4-hour observation period. Several times the westward electric field inside large regions of enhanced electron density was substantially smaller than the field outside these regions. In addition, on several occasions these walls or bands of ionization were found to drift southward at about the same speed as the E⊥ × B drift in the surrounding plasma. The plasma inside the enhanced region, however, did not share the drift motion but remained relatively stationary with respect to the radar. The present observations of F2 layer densities and temperatures indicate an unusual increase in electron density just before the onset of a large substorm. Finally, measurements of the height and peak density of the auroral E layer show significant variations in the intensity and average energy of the electron flux. These variations appear to be related to auroral breakup and a transition to steady precipitation of moderately soft electrons.