Spatiotemporal characteristics of lake breezes over Lake Taihu, China

Lake Taihu is a shallow lake located in the Yangtze River delta region in eastern China. Lake breezes and their interactions with urban heat islands are of great importance to air quality andweather forecasting. In this study, surface observations at a dense network and Wind Profile Radar measurements were utilized to characterize the lake breezes at Lake Taihu and assess the impact of geophysical factors on the development and intensity of the lake breezes. The lake breezes were characterized by a low occurrence frequency of 12%– 17% (defined as the percentage of days with lake breezes in a givenmonth), weak speed (annualmean ranging from 1.5 to 3.3m s), late onset [average onset around 1110 local standard time (LST), with a range of 0900– 1300 LST], short duration (annual mean 3.5 h), and low circulation depth (average depth of 400m from 1200 to 1400 LST). The lake breezes were greatly suppressed when the geostrophic winds were higher than 4.1m s. The low heat capacity of shallow water (mean depth 2.0m) led to small temperature differences between the land and the lake, which was the main factor responsible for the low occurrence frequency along Lake Taihu. All of the characteristic parameters showed distinct seasonal variations. Increased frequencies, earlier onset times, and longer durations on the northern lakeshore were indicative of the impact of the urban heat island on the lake breezes.