Nighttime variations ofF-region electron density profiles at Puerto Rico

The origin of the time-dependent variations of nighttime F-region electron density profiles is investigated. Assuming a model atmosphere, the set of parameters that best satisfies the continuity equation over a wide range of height in the F region has been determined from observational data for midnight in March 1959. A scale height for atomic oxygen of 70 km and diffusion coefficient of 5×109 cm2 sec−1 were obtained for the scale height gradient 0.2 and attachment coefficient 10−4 sec−1 at 300 km. Then the vertical drift velocities were calculated every ten kilometers for each hour. Two cases are considered: one in which the temperature distribution varies with time, and one in which temperature distribution is constant with time. The first case takes into account the effect of the change in attachment and diffusion coefficient at 300 km due to a change in temperature distribution, and the result shows a very reasonable decrease of temperature (about 15 per cent) during the night, making the drift velocity at higher regions very small. The second case gives a remarkable semidiurnal vertical drift velocity with almost the same phase as that calculated from wind systems by dynamo theory. Both results seem equally realistic, but a combination of the two effects, drift velocity and temperature change, may better explain the observational results.