Features of Air-Lake Interaction in Heat and Water Exchanges over Erhai Lake

This paper presents the characteristics of air-lake-land interactions, which arise from the different thermal properties of lake and land surfaces, as observed at Erhai Lake in Yunnan Province, China. The heat balance over the lake was estimated by using data on the lake surface obtained from the Erhai automatic weather station and solving the surface heat balance equation (HBE) for a mixed layer. Meteorological station data were also used to estimate the long-term heat balance. The surface temperature from in situ observations was compared with that from satellite observations, and the two results were found to be in reasonably good agreement. The satellite data were used to validate the heat balance calculation. The mixed layer depth of Erhai Lake was 6 m in 2008 and 8 m from 2003 to 2008. Lake heat storage showed large annual variation of 50 W m(-2) in amplitude, with a maximum from March to April and a minimum in November. The phases of the latent heat, the sensible heat, and the difference between surface and air temperatures tended to be delayed on the lake as compared with the land. The phase lag in the seasonal variation of evaporation was found to clearly depend on lake depth. The daily change in convection over the lake-land system was greatest in the daytime over the mountainous area and in the nighttime over the lake area. These features arose from differences in the thermal properties of the lake and land surfaces. Non-dimensional evaporation increased with increasing annual mean air temperature, and there was no systematic difference between regions. Nearly 92% of solar radiation was absorbed by the lake within a depth of 2 m. From this finding, the daily range of the lake's surface temperature was quantitatively determined to be about 5 degrees C.