131. Radiation balance map

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Radiation and thermal balance of water surface

Absorbed solar radiation is the main thermal source of the lake water column. It depends on incident solar radiation and the ratio of reflected radiation (albedo). Thus, it has a well-defined seasonal trend. Radiation balance of the Lake Baikal water surface is a sum of absorbed solar radiation and effective radiation of water surface. This balance is positive from April to September and negative from October to March. In general, radiation balance of the lake is positive throughout the year, changing from 1,900 MJ/m² in the Selenga river area to 700-800 MJ/m² in the northern part of the lake. Spatial distribution of radiation balance of the lake surface depends on cloud regime during warm period. Radiation balance varies insignificantly because of inconsiderable changes of the cloud cover. In cold period, the distribution of radiation balance is influenced not only by the cloud cover but also by the difference in the albedo of water and snow. Therefore, the radiation balance in Northern Baikal is much lower than that in Central and Southern Baikal. Radiation balance of the water surface is a determining element in the thermal regime of the lake. Because of high water heat capacity, constant time lag is recorded in the seasonal trend of temperature parameters in comparison with radiation characteristics. Therefore, maximal accumulated radiation and radiation balance are recorded at Lake Baikal in June and the highest air and water temperatures in August.