Characteristics of Lake Breezes and Their Impacts on Energy and Carbon Fluxes in Mountainous Areas

Abstract

In mountainous lake areas, lake-land and mountain-valley breezes interact with each other, leading to an “extended lake breeze”. These extended lake breezes can regulate and control energy and carbon cycles at different scales. Based on meteorological and turbulent fluxes data from an eddy covariance observation site at Erhai Lake in the Dali Basin, southwest China, characteristics of daytime and nighttime extended lake breezes and their impacts on energy and carbon dioxide exchange in 2015 are investigated. Lake breezes dominate during the daytime while, due to different prevailing circulations at night, there are two types of nighttime breezes. The mountain breeze from the Cangshan Mountain range leads to N1 type nighttime breeze events. When a cyclonic circulation forms and maintains in the southern part of Erhai Lake at night, its northern branch contributes to the formation of N2 type nighttime breeze events. The prevailing wind directions for daytime, N1, and N2 breeze events are southeast, west, and southeast, respectively. Daytime breeze events are more intense than N1 events and weaker than N2 events. During daytime breeze events, the lake breeze decreases the sensible heat flux (Hs) and carbon dioxide flux ($\boldsymbol{F}_{\text{CO}_{2}}$) and increases the latent heat flux (LE). During N1 breeze events, the mountain breeze decreases Hs and LE and increases $\boldsymbol{F}_{\text{CO}_{2}}$. For N2 breeze events, the southeast wind from the lake surface increases Hs and LE and decreases $\boldsymbol{F}_{\text{CO}_{2}}$. Results indicate that lakes in mountainous areas promote latent heat mixing but suppress carbon dioxide exchange.

摘要

高原湖区周边地形复杂多样, 湖陆风环流与山谷风环流叠加, 形成的局地环流具有复杂性和独特性, 对局地的能量和物质循环产生显著影响. 基于2015年洱海的涡动观测资料, 分析了湖陆风和山谷风对能量通量和CO₂通量交换的影响. 研究结果表明, 白天湖风促进潜热通量的交换, 减少感热通量和CO₂通量交换. 夜间山风增加CO₂通量交换, 减少感热通量和潜热通量交换. 夜间来自湖面的东南风促进感热通量和潜热通量交换, 抑制CO₂通量交换. 相对于山地其他下垫面类型, 湖泊增加局地的潜热交换, 减少CO₂通量交换.