Spatiotemporal characteristics of lake breezes over Lake Taihu, China

Abstract

ake Taihu is a shallow lake located in the Yangtze River Delta region in East China. Lake breezes and their interactions with urban heat islands are of great importance to air quality and weather forecasting. In this study, surface observations at dense network and Lidar Wind Profiler 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 to 17% (defined as the percentage of days with lake breezes in a given month), weak speed (annual mean ranging from 1.5 to 3.3 m·s-1), late onset (average onset around 11:10 local standard time (LST), with a range of 09:00?13:00 LST), short duration (annual mean 3.5 hours), and low circulation depth (average depth of 400 m from 12:00?14:00 LST). The lake breezes were greatly suppressed when the geostrophic winds were higher than 4.1 m·s-1. The low heat capacity of shallow water (mean depth 2.0 m) 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. Finally, 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.