Evidence of anisotropic temperatures of molecular ions in the auroral ionosphere

Using incoherent scatter measurements obtained from Kiruna and Sodankyla EISCAT remote stations, and corresponding to different aspect angles, the authors show, for the first time, anisotropic temperatures of molecular ions. The electric field obtained for the 5 hours period of the 2nd February 1990 experiment presented here range from 20 to 50 mV/m. They show that the line of sight ion temperature deduced from Kiruna incoherent scatter spectra is larger than the one deduced from Sodankyla spectra which correspond to a smaller aspect angle. A statistical approach has been chosen to evaluate a β parameter for Sodankyla measurements which describes the anisotropy. They found a value of 0.60 ± 0.02 which compares very well with values inferred from theoretical studies