Electron‐to‐ion temperature ratio from radar Thomson scatter observations

Radar Thomson scatter observations made at the Arecibo Ionospheric Observatory on August 10, 1966, are reported. Analysis of the ion and plasma line components of the Thomson scatter signal from the ionosphere provided two essentially independent methods of obtaining the electron-to-ion temperature ratio Te/Ti. In the first method, Te/Ti and Ti were deduced from the shapes of the autocorrelation functions of the ion component by using assumed values for the ion composition. In the second method values of Te/Ti were derived from the radar equation for Thomson scatter using electron concentrations from the plasma line observations and power measurements of the ion component. Altitude profiles of Te/Ti from these two methods were compared over the range 130 to 450 km and were found to be in excellent agreement. At 130 km Te/Ti was unity, and this result does not support the conclusion drawn from many midlatitude rocket observations that an E-region source of electron heating exists in addition to solar EUV. Above 130 km the electron temperature was always greater than the ion temperature for daytime conditions. A downward heat flux of 1.7±0.3×109 ev cm−2 sec−1 near local noon was inferred from the positive Te gradient at 400 km. The plasma line measurements provided accurate electron concentration (ne) profiles in close agreement with simultaneous ionosonde determinations. Composite profiles of Te/Ti, Ti, and ne are presented for different times throughout the day.

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