The collision frequency in the E- and D-regions of the ionosphere

The height variation of collision frequency, v, is critically discussed using both measured data and computations based on Pack and Phelp's cross-sections applied to standard atmospheres. Up to about 80 km excellent agreement is found and both methods give a significant seasonal variation of v at constant height. In the E-region large discrepancies are found which increase to a factor of 10 near 130 km. It is not possible to decide uniquely whether v in the E-region is large, in agreement with the experimental data, or small as expected from the pressures of the standard atmosphere. The importance of the distinction is stressed and some possible reasons for the discrepancy are discussed.

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