Abstract
Under the condition of land-atmosphere heat and water conservation, a set of sensitive numerical experiments are set up to investigate the response of the East Asian climate system to global frozen soil change. This is done by introducing the supercooled soil water process into the Community Land Model (CLM3.0), which has been coupled to the National Center of Atmospheric Research Community Atmosphere Model (CAM3.1). Results show that: (1) The ratio between soil ice and soil water in CLM3.0 is clearly changed by the supercooled soil water process. Ground surface temperature and soil temperature are also affected. (2) The Eurasian (including East Asian) climate system is sensitive to changes of heat and water in frozen soil regions. In January, the Aleutian low sea level pressure circulation is strengthened, Ural blocking high at 500 hPa weakened, and East Asian trough weakened. In July, sea level pressure over the Aleutian Islands region is significantly reduced; there are negative anomalies of 500 hPa geopotential height over the East Asian mainland, and positive anomalies over the East Asian ocean. (3) In January, the southerly component of the 850 hPa wind field over East Asia increases, indicating a weakened winter monsoon. In July, cyclonic anomalies appear on the East Asian mainland while there are anticyclonic anomalies over the ocean, reflective of a strengthened east coast summer monsoon. (4) Summer rainfall in East Asia changed significantly, including substantial precipitation increase on the southern Qinghai-Tibet Plateau, central Yangtze River Basin, and northeast China. Summer rainfall significantly decreased in south China and Hainan Island, but slightly decreased in central and north China. Further analysis showed considerable upper air motion along ∼30°N latitude, with substantial descent of air at its north and south sides. Warm and humid air from the Northeast Pacific converged with cold air from northern land areas, representing the main cause of the precipitation anomalies.
Highlights
Introduction to Community Atmospheric Model (CAM)CAM3.1 of National Center for Atmospheric Research (NCAR) was adopted, for the following reasons: (1) Both CAM and Community Land Model (CLM) are numerical models with full two-way coupling; and (2) CAM is an open model whose program is obtained, with greater portability and application
This is done by introducing the supercooled soil water process into the Community Land Model (CLM3.0), which has been coupled to the National Center of Atmospheric Research Community Atmosphere Model (CAM3.1)
Many improvements and optimizations have been made in the CAM3.1 physical process [25]
Summary
CAM3.1 of NCAR was adopted, for the following reasons: (1) Both CAM and CLM are numerical models with full two-way coupling; and (2) CAM is an open model whose program is obtained, with greater portability and application. The new freezing condition becomes as follows: When soil volumetric water content is greater than lmax and soil temperature is less than 0°C, the excess part will be frozen. It is seen from eq (3) that the maximum volumetric water content (below freezing point) is inversely proportional to soil temperature, but proportional to the effective soil porosity (soil property). We used a set of meteorological and hydrological data spanning 18 years (1966–1983), from Valdai frozen soil observation station in the former Soviet Union, to validate the new freezing condition In Layer 4 (0.12 m) of the model, the 16-year average reduced ice content accounts for 19.1% of total water amount in this layer
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