Characterization and modeling of the upper atmosphere's midnight temperature maximum using ground-based optical observations.

摘要

The thermosphere is defined as the portion of the Earth's upper atmosphere above about a hundred kilometers where neutral temperature increases with altitude due to solar input. The resulting thermal patterns influence atmospheric dynamics over the globe. The ultraviolet components of sunlight also ionize a portion of the thermosphere, forming an ionosphere which varies in space and time. After sunset the ionosphere decays but thermospheric temperature develops an anomalous increase near the geographic equator called the midnight temperature maximum (MTM) which exhibits apparent poleward propagation. The MTM significantly impacts fundamental upper atmospheric parameters, requiring attention to be focused on its characteristics and generation mechanisms.; This dissertation presents the first two-dimensional, ground-based observations of the MTM through its enhanced airglow signature, the midnight brightness wave (MBW), observed by the Arequipa, Peru all-sky imaging system. Correlated Fabry-Perot interferometer measurements of temperature and winds provide the corroborating evidence for this relationship. The combined fields of view of the Arequipa imager and those at Tucuman and El Leoncito, Argentina, extend latitudinal surveillance of the MTM's poleward propagation through 39°S, providing the first indication that the MTM's influence on the upper atmosphere stretches to mid-latitudes.; The Arequipa all-sky imaging database, October 1993 to December 1999, includes the largest collection of MTM observations to date. Using this database, this work presents the first characterization of MTM occurrence rates, times, and magnitude in terms of solar and magnetic activity.; To address physical mechanisms, several models for MTM effects are examined. The National Center for Atmospheric Research (NCAR) Thermosphere-Ionosphere-Electrodynamic General Circulation Model (TIEGCM) proves only partially successful in reproducing the MTM through inclusion of upward propagating semi-diurnal (12-hour) tidal oscillations excited in the lower atmosphere. The role of additional tidal oscillations is addressed through comparison of MBW observations with TIEGCM and Naval Research Lab (NRL) ionospheric model airglow simulations. The first successful MBW simulation is presented through modification of the NRL model to include analytic meridional wind equations derived from radar measurement and theoretical tidal calculations. Harmonic decomposition of TIEGCM and NRL modeled meridional winds indicates the importance of phase in MTM development.