Global atomic hydrogen density derived from OGO-6 Lyman α measurements |
| |
| Authors: | GE Thomas Donald E Anderson |
| |
| Institution: | Department of Astro-Geophysics and Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80302, U.S.A. |
| |
| Abstract: | Measurements of the Lyman α airglow intensity were made between June 1969 and June 1970 by a u.v. photometer experiment on the OGO-6 satellite. The data for the zenith intensity at altitudes between 400 and 1100 km were fitted to theoretical airglow models to derive atomic hydrogen density nc at a reference altitude, taken to be 500 km. nc was determined for each of 286 orbits throughout the year. The mean exospheric temperature T∞(J) during this period varied from 900 to 1300 K according to the Jacchia model. The solar Lyman α flux at line center F0 was also determined over each 90-min orbit in the model-fitting procedure. F0 was found to be correlated with sunspot number, in agreement with previous results. A nearly-exact linear relationship was found for F0, when averaged over ‘bins’ which are 20 sunspot numbers in width. nc was found to be inversely correlated with T∞(J); however the dependence is not that predicted by steady-state models whose only escape mechanism is Jeans evaporative escape. Unless the total atmospheric loss rate depends upon 27-day changes in the solar EUV, which is unlikely, an additional upper atmospheric loss is required in order that the total loss remain constant with T∞(J). This extra loss may be largely due to charge-exchange reactions in the exosphere, wherein energetic protons are converted to fast hydrogen atoms, as suggested previously by a number of authors. An additional result is suggested by the apparent spherical symmetry of the inferred density, namely that the familiar diurnal variation of hydrogen is absent at the high latitudes preferentially sampled by the OGO-6 data. |
| |
| Keywords: | |
| 本文献已被 ScienceDirect 等数据库收录！ |
|
