Date of Award
2024
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Atmospheric and Earth Science
Committee Chair
Leiqiu Hu
Committee Member
John R. Mecikalski
Committee Member
Sean Freeman
Committee Member
Arastoo Pour Biazar
Committee Member
Lulin Xue
Research Advisor
Leiqiu Hu
Subject(s)
Urban heat island, Clouds, Forest canopies
Abstract
Understanding land-atmosphere (L-A) interactions is critical for predicting Earth’s system and its functionality. This dissertation advances knowledge in three aspects involving L-A interactions at different scales. The first study asks how city-wide tree canopy temperatures vary diurnally, and what environmental factors and to what extent they contribute to its spatiotemporal variation. Despite the importance of urban trees’ surface temperature in assess-ing micro-climate interactions between trees and the surrounding environment, their diurnal evolution has been largely understudied at a city-wide scale. The research highlights the more important role of the greenspace coverage in controlling the daytime canopy temperature, while, surrounding buildings modulate canopy temperature asymmetrically diurnally: reduced daytime warming and reduced nocturnal cooling. The second study unveils how cities modify local cloud patterns and how regional climate and local urban properties influence the diurnal and seasonal changes of urban cloud patterns. Cloud is one of the critical components in regulating urban hydrometeorological cycles but remains less understood in urban-atmospheric systems. The research reveals that most cities experience enhanced cloudiness in the summertime diurnally, while, asymmetric diurnal effects in the wintertime. City size and stronger surface heating are primarily responsible for summer local cloud enhancement diurnally; while moisture and energy background control the urban cloud cover anomalies seasonally. The last study improves understanding of 40yr spatiotemporal dynamics of cloud pattern changes across CONUS and its sub-regions. There is a lack of long-term knowledge of spatial and temporal dynamics of cloud trends and variability at sub-regional scales due to a lack of effective cloud datasets. Cloud representation remains challenging in climate modeling. The cloud climatological analysis built on observation-validated advanced model simulations suggests that overall cloud frequency has been declining in the first three decades and slightly increased in the most recent decade at an average rate of −0.06%yr−1 across CONUS, and there is a more rapid changing rate over sunny regions. The long-term decreasing trends were found for all three cloud types (high, mid, and low clouds) across CONUS, but, their relative changes to total clouds are rather different. Improved understanding of such phenomena in L-A interactions extends our knowledge of the critical processes and helps to untangle the complex interactions in the climate system.
Recommended Citation
Vo, Thuy Trang, "Land-atmosphere interactions over cities : urban effects on tree canopy temperature and local cloud patterns" (2024). Dissertations. 431.
https://louis.uah.edu/uah-dissertations/431