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Field Observation of Different Wind‐Induced Basin‐Scale Current Field Dynamics in a Large, Polymictic, Eutrophic Lake
Author(s) -
Wu Tingfeng,
Qin Boqiang,
Ding Wenhao,
Zhu Guangwei,
Zhang Yunlin,
Gao Guang,
Xu Hai,
Li Wei,
Dong Baili,
Luo Liancong
Publication year - 2018
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1029/2018jc014040
Subject(s) - wind stress , environmental science , current (fluid) , stratification (seeds) , thermal wind , climatology , wind speed , atmospheric sciences , structural basin , monsoon , oceanography , geology , wind shear , geomorphology , seed dormancy , botany , germination , dormancy , biology
Basin‐scale current fields are fundamental to determining the environmental characteristics and ecological attributes of large polymictic lakes. However, little is known concerning the effects of different winds on the currents and further on ecological systems of these lakes. Therefore, synchronous meteorological and hydrological data were collected from Lake Taihu (China) during summer 2015. Time series analysis and stress calculations conducted to elucidate the basin‐scale current field revealed frequent occurrence of a bilayer current mode, comprising a wind‐driven surface current and bottom compensation current, under low or medium wind conditions. The main forcings of the lake currents are seasonal winds related to the East Asian monsoon, and the lake‐land thermal contrast wind with 24‐hr periodicity causes marked diurnal fluctuation. Inflows, outflows, the Coriolis force, and bottom frictional stress also make important contributions to the bilayer current mode, and weak temperature stratification can stabilize this mode. However, as wind speed increases, wind‐driven surface currents can develop downward to form uniform currents throughout the water depth, and water temperature stratification is destroyed during typhoon‐affected periods. During such short‐term strong wind events, the current structure mainly adopts a monolayer current mode and the incidence of the bilayer current mode decreases substantially. The monolayer current mode causes a clockwise circulation and a basin‐scale temporary oscillation with ~80‐hr periodicity. The influences of the monsoon and lake‐land thermal contrast wind on lake currents were masked by the pulse‐like strong winds. Both modes can contribute to persistent cyanobacterial blooms in the northwest of Lake Taihu.