Observation of the energy distribution of thermal electrons in the winter predawn ionosphere by a K-9M-76 rocket

This paper is concerned with the electron energy distribution in the winter predawn ionosphere measured by a Langmuir probe on board a K-9M-76 rocket. The rocket was launched on January 15, 5h40m a.m., 1983, from Kagoshima Space Center to study the predawn enhancement of airglow and the behavior of photoelectrons from a magnetically conjugate region. The measurement of thermal electrons was made by applying the Druyvesteyn method to evaluate the production rate of O (1D) through dissociative recombination of electrons with O2+ and the heating rate by Coulomb collision. For the double differentiation of the probe current, delay circuits were used, which were favorable for the high speed scanning. Energy distribution f(E)/√E showed nearly Maxwellian except in the extreme low energy part. Certain wriggles were superimposed on the higher energy part. A double-hump structure appeared in the low energy part at lower heights (E-F valley between 140 and 230 km and E-layer around 90km). The electron temperature, Tsub(e), determined from the least square fitting on the semilog plot of the differentiated probe characteristics was about 7500K near 90km (E layer), showing a gradual increase with height to about 13000K at 350km (F layer). The value of Tsub(e) in the downleg showed a higher value by 20 to 30% than that in the upleg. The reason may be partly due to the interaction between photoelectrons and thermal electrons and partly due to an apparent increase by the wake. (author)