Studies of thermospheric neutral winds utilizing ground-based optical and radar measurements.

The neutral dynamics of the F-region and the lower thermosphere have been investigated through extensive ground-based measurements. Ground-based Fabry-Perot Interferometers at Thule Air Base (76.5$\sp\circ$ N, 68.4$\sp\circ$ W) and Sondre Stromfjord (67.0$\sp\circ$ N, 50.9$\sp\circ$ W), Greenland, are utilized to investigate high-latitude neutral dynamics in the F-region ($\sim$250 km) by observing the (OI) 6300 A emission line profiles. They are also used to study the lower thermospheric region ($\sim$97 km) by observing the (OI) 5577 A line profiles. The high-latitude mean neutral winds in the F-region thermosphere vary significantly with changes in the level of solar activity and geomagnetic condition due to the direct and indirect influence of high-latitude magnetospheric and ionospheric processes. Careful treatment is used in analyzing the (OI) 5577 A measurements because of the possible contamination from auroral emission and weak F-region emission. The ambiguity in the altitude of the emission layer is removed by eliminating data with relatively high signal intensity, because the auroral emission contribution is always much greater than the nightglow. The contribution originating from the upper layer to the measured winds has been quantified by performing a computer simulation. The simulation results indicate that the measured winds at Thule may have a substantial diurnal oscillatory component from the F-region. The same simulation shows negligible F-region contamination for Sondre Stromfjord winds. Tidal information is extracted from the averaged winds and compared with radar measurements in similar locations and model output. The global structure of lower thermospheric dynamics is investigated utilizing a comprehensive data base of lower thermospheric wind measurements. Data are assembled from various radar systems. The data, together with FPI measurements, are used to develop an empirical model of global lower thermospheric diurnal and semidiurnal tidal oscillations. The amplitudes of tidal oscillations generally increase with height in the lower thermospheric region.PhDAtmospheric and Space SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/104056/1/9423347.pdfDescription of 9423347.pdf : Restricted to UM users only