Cities modify regional cloud cover
Abstract
Urbanization extensively modifies surface properties and roughness, influencing regional climate and hydrological cycles. Despite growing attention on how cities impact regional temperature and precipitation, how they impact regional cloud dynamics, motion, and formation remains the least understood in the urban-atmosphere system. As clouds are one of the important elements that are closely linked to radiative balance and hydrological cycle, an improved understanding of their patterns in urban environments will further advance the understanding of urban hydrometeorological cycles.
We analyzed and quantified the spatial and temporal anomalies of cloud cover induced by 447 U.S. cities based on recent 2-decade continental-scale satellite observations. The systematic assessment suggests that there is a strong seasonality of urban-induced cloud modification. Most cities have experienced enhanced daytime cloud cover in both summer and winter; enhanced nocturnal clouds prevail in the summertime (5.8 %) while there is a modest suppression of urban clouds during wintertime. Then, we statistically investigated how city properties, geographical locations, and climate backgrounds influence on their regional cloud patterns. We found that at night, city size and surface heating mainly contribute to the enhanced local clouds. Moisture and energy background is more responsible for the daytime urban cloud signals. Strong regional mesoscale circulations, such as land-sea and orography-induced breezes, further alter local cloud patterns in a more complicated way. Our observational research of cloud cover across all-sized U.S. cities across different climate backgrounds and geographical locations unveil, for the first time, the fact that the city itself locally modifies the regional cloud cover, but, importantly, to what extent this local effect is active largely depends on regional factors. Our findings highlight the need for improving the understanding of cloud life cycles in the urban climate system.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2022
- Bibcode:
- 2022AGUFM.A26B..02V