Non-Isotropic Ion Temperature Distributions in the Auroral F-Region as Measured with EISCAT

The EISCAT UHF system measured ion temperatures at 240, 270, and 300 km altitude. Results show that nonmaxwellian ion velocity distributions occur in the auroral F-region. The ion temperature enhancements are caused by Joule heating. However, without measurements of the neutral wind it is not possible to state if a bi-Maxwellian description is appropriate or if a stronger deviation from the Maxwellian ion velicity distribution is present.