Diagnosing the strength of soil temperature in the land atmosphere interactions over Asia based on RegCM4 model

Abstract This study aims to investigate the soil temperature atmosphere (ST Atm) coupling strength and their influence on the subsequent climate anomalies over Asia based on a regional climate model RegCM4 with both statistical analysis method and numerical experiments. The major findings are as follows: (1) The soil temperature precipitation (ST P) coupling is quite weak and spatially scattered from both RegCM4 output and GLDAS data in each season with the only obvious signals existing over the north India region in summer season according to the RegCM4 output; the soil temperature 2m air temperature (ST T2m) coupling is strong and spatially continuous with the India (in spring, summer and autumn seasons), South Indochina (in spring and summer seasons) and part of North China (in summer season) standing out as hotspots. (2) The soil temperature evapotranspiration (ST ET) and soil temperature evaporative fraction (ST EF) coupling almost resembles the same spatial patterns and magnitude in each season. Both the ET and EF play an important role in linking ST P coupling in each season, but not in the ST T2m coupling. The hotspots of ST T2m coupling outweigh the areas with strong ST ET and ST EF coupling. Only the India and Indochina in each season are recognized by the RegCM4 while the Indochina and west Asia in spring, north India, Indochina and part of mid-high latitudes in summer season pinpointed by GLDAS data show consistent strong ST T2m coupling with significant ST ET and ST EF coupling. This finding demonstrates the complicated ST Atm coupling. (3) The ST anomalies prescribed at the first step of each season can only persist a short time (within 5 days) over most part of the study area while the fixed one-month anomalies can last longer (approximately 2 months with colder anomalies and 45 days with warmer anomalies in tropical regions). (4) The impact of ST anomalies on subsequent precipitation is quite weak and can be ignored over most part of the study area, while the impact on subsequent T2m is obvious and spatially continuous. The spatial patterns for the changes of climate variables (e.g., latent heat flux (LH), sensible heat flux (SH), ET, T2m) are almost consistent with the changes of ST over most part of the study area (except India and Indochina in spring and autumn seasons) where warmer (colder) ST anomalies lead to increase (decrease) of LH, SH, ET and T2m, demonstrating the important role of land atmosphere interactions in the locale climate. Over the India and Indochina, the large-scale circulation dominates the local climate in spring and autumn seasons. (5) The impact of colder ST anomalies can last longer than the warmer ones. Among the spring, summer and autumn seasons, the impact persists shortest in summer and longest in autumn, especially over the India region.