Date of Award
Doctor of Philosophy (PhD)
Aerospace Engineering Sciences
McMurdo lidar campaign provides invaluable data for studies of the polar middle and upper atmosphere. The science topics to be addressed in this dissertation are the temperature tides (30–110 km) and temperature climatology (0–110 km). Tides are important to the dynamic and chemical processes in the middle and upper atmosphere. Tides, for examples, can obtain large amplitudes in the middle and upper atmosphere, where they modulate ionospheric variability via the E-region dynamo effect, enhance vertical atmosphere coupling and cause instabilities by inducing significant temperature gradients and wind shears. However, observations of tides in the Antarctic region are rare, especially for temperature tides. In this dissertation, we present lidar measurements of winter tides from 30 to 110 km at McMurdo (77.8°S, 166.7°E). The observed diurnal and semidiurnal tides indicate small amplitudes (less than 3 K) below 100 km, but above 100 km, we observed fast growth of tidal amplitudes to at least 15 K near 110 km, exceeding that of the freely propagating tides originating from the lower atmosphere. Such fast growth of tidal amplitude raises questions regarding the identification of sources of the tides above 100 km and how these sources are related to geomagnetic activities or other factors.
We utilized the Coupled Thermosphere Ionosphere Plasmasphere Electrodynamics (CTIPe) model to further investigate the questions raised. Simulations with the CTIPe model reproduce the lidar observations and exhibit a concentric ring structures of diurnal amplitudes encircling the south geomagnetic pole and overlapping the auroral zone. These findings point to a magnetospheric source origin. Mechanistic studies using CTIPe show that the adiabatic cooling/heating associated with Hall ion drag is the dominant source of this feature, while Joule heating is a minor contributor due to the counteraction by Joule-heating-induced adiabatic cooling. The sum of total dynamical effects and Joule heating explains ~80% of the diurnal amplitudes. The auroral particle heating, lower atmosphere tides, and direct solar heating have minor contributions, according to the CTIPe model.
In the polar region, temperature controls numerous geophysical phenomena and is also a key variable in climate change studies. We derived the temperature climatology from the ground to 110 km at McMurdo based on the 4 years of lidar and radiosonde observations, and applied the backward differtiation method to fill in the data gaps. The climatology is compared with model outputs and satellite measurements. The latitudinal dependences of stratopause and mesopause temperature were found between different Antarctica stations. The McMurdo lidar campaign also demonstrated the potential to push the temperature climatology lid altitude to 120 km during winter, where measurements are extremely rare.
Finally, we utilize the forward model method to assess how PMT non-linear response and laser pulse spectrum affect the temperature and radial wind measurements of a 3-frequency Na Doppler lidar. As the polar region from 100 to 200 km is the least understood and most sparsely observed region, the tidal study presented here will help improve the current understanding of how the wave coupling between the ionosphere plasma and the neutral thermosphere. Also, the establishments of the temperature climatology and temperature calibration not only reveal the thermal structure at McMurdo, but also provide references for the future studies. The calibrated temperature data will serve as the baseline for comparison with measurements made decades in the future, and the calibration methods we developed will be a guideline for the lidar field.
Fong, Weichun, "Lidar Observations and Modeling Studies of Antarctic Temperature Tides at McMurdo & Establishment of Temperature Climatology with Calibrated Fe Boltzmann and Na Doppler Lidars" (2015). Aerospace Engineering Sciences Graduate Theses & Dissertations. 106.