Observation and Process Understanding of Typical Cloud Holes Above Lakes Over the Tibetan Plateau

Abstract

AbstractUnderstanding cloud distribution over lakes is crucial to determine input radiation and precipitation for lake thermal and water balance processes. Based on Himawari‐8 satellite observation and Weather Research and Forecasting model results, this study examines the influences of lakes on daytime cloud cover during warm seasons over the Tibetan Plateau (TP), which is home to thousands of lakes. Observation shows the existence of cloud holes and narrow cloud rings around the lakes, that is, fewer clouds over the lakes and more clouds along the shoreline, which has rarely been reported and is considered typical to TP by comparison with lakes outside of TP. The threshold size of lakes that can produce the shoreline cloud ring is identified to be about 300 km2, as a conservative estimate. We further highlight the importance of atmosphere advection/background wind in the formation of lake‐associated clouds. Lake breeze forms under weak background winds and the downdraft branch inhibits cloud formation over the lakes; while the updraft branch causes convection to form clouds over lakeshores. However, strong background winds do not favor lake breeze formation, changing cloud distribution over the lakes. Fewer clouds are also found in the downwind regions, and this influence is at a distance comparable to the lake scale. Due to fewer clouds over lakes, shortwave radiation is significantly larger (∼100 W/m2) and longwave radiation is smaller (∼a few W/m2) than that of the further land region. Therefore, the above observational facts provide a new perspective to advance the understanding of lake‐air interactions.