Comment on tc-2021-398

doi:10.5194/tc-2021-398-rc1

Abstract

Ngoring Lake is the largest freshwater lake in the Qinghai-Tibet Plateau (TP). The lake water temperature was observed to be generally rising during the ice-covered period from November 2015 to April 2016. This phenomenon appeared in the whole water column, with slowing in deep water and accelerating in shallow water before ice melting. The process is different from low-altitude boreal lakes. There are few studies on its mechanism and effects on lake-atmosphere interaction. Based on the observation data of Ngoring Lake Station, ERA5-Land data, MODIS surface temperature data, and precipitation data of Maduo Station of China Meteorological Administration, the characteristics of water temperature rise in the ice-covered Ngoring Lake are analyzed. LAKE2.3 model, which is currently little used for TP lakes, is applied to explore the influence of local climate characteristics and the main physical parameters on the radiation transfer in water body. The study questions are the continuous rise of water temperature in the ice-covered period, and the effects of different water temperature profiles prior to ice breakup on the lake heat storage per unit area and sensible and latent heat release. The results show that LAKE2.3 represents well the temperature evolution and thermal stratification in Ngoring Lake, especially in the ice-covered period. The strong downward short-wave radiation plays a dominant role, low precipitation gives positive feedback, and smaller downward long-wave radiation, lower temperature and larger wind speed give negative feedback. Increase of ice albedo and ice extinction coefficient reduces the heating rate of water temperature before reaching the maximum density temperature, and increases the maximum temperature that can be reached during ice-covered period, while increasing the water extinction coefficient has little influence on water temperature. The lake temperature in Ngoring Lake rising during the ice-covered period, and the temperature at the upper layer of lake body was higher than that at the maximum density temperature before ice breaking. Compared with the characteristics of three typical ice-covered periods which the lake temperature remained fixed in each layer, and the lake temperature was less than or equal to the maximum density temperature, the difference of heat release after ice breaking lasted for 59–97 days. The higher the lake temperature before breakup, the more heat is stored in the lake, and the more sensible heat and latent heat is released when the ice melts completely and the faster is the heat release.

Highlights

The Tibetan Plateau (TP), with an average altitude of 4000-5000 m, is known as the "roof of the world"
Compared with the characteristics of three typical ice-covered periods which the lake temperature remained fixed in each layer, and the lake temperature was less than or equal to the maximum density temperature, the difference of heat release after ice breaking lasted for 59-97 days
The water temperature was slightly higher from mid-March to the end of May in the model compared with observations, and there were differences in the simulation of deep layers

Summary

Introduction

The Tibetan Plateau (TP), with an average altitude of 4000-5000 m, is known as the "roof of the world". It is the highest plateau on Earth. There are many alpine lakes in TP constituting the largest number, largest area and highest altitude plateau lake group in China, known as the "Asian water tower" (Immerzeel et al, 2010). Under the background of global warming, the surface temperature of lakes has been rising (O'Reilly et al, 2015; Schmid et al, 2014; Sharma et al, 2015; Zhang et al, 2014). The material and energy exchange between the lake and the atmosphere depend on the surface temperature (Efremova et al, 2013; Ramp et al, 2015; Rösner et al, 2012) that has impact on the local climate (Gerken et al, 2013; Li et al, 2016a; Wen et al, 2015; Xu and Liu, 2015; Yang and Wen, 2012)

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Conclusion