Collision frequencies in the D-region

Partial reflection differential absorption and differential phase observations have been used to systematically study collision frequencies ( ν) in D-region of the lower ionosphere. The observations made with the large MF radar located at Buckland Park (35° S, 138° E) near Adelaide in the period September 1996–December 2000 show ν values larger than predicted by previously used models. The new estimates are compared with values calculated using new collision frequency momentum cross-sections for N 2( σ) measured in the laboratory. The two types of measurements are found to be in good agreement, with a moderate seasonal variation of ν at a constant height. No change due to solar cycle variations is found.