Assessing land-atmosphere coupling using soil moisture from the Global Land Data Assimilation System and observational precipitation

Precipitation analysis and soil moisture from the Global Land Data Assimilation System (GLDAS) are used to assess the land-atmosphere coupling in boreal summer. Correlations between antecedent soil moisture and precipitation suggest that regions of strong land-atmosphere coupling lie mainly in arid to semiarid transition zones or in semihumid forest to grassland transition zones. They consist of central Eurasia, the region from Mongolia to northern China, southwest China, the Sahel, the northern continental United States, and southern Europe. It is found that over these regions, positive soil moisture feedback accounts for typically 10-20% of the variance of monthly precipitation anomalies with the feedback efficiency of the order of 0.3-0.9 mm month(-1) (0.1 standardized soil moisture)(-1). While soil moisture feedback is dominated by the positive sign, negative feedback may exist in some areas, such as India and the western part and Quebec province of Canada. Generally, the land-atmosphere coupling strength estimated from the GLDAS data agrees well with those from the observational soil moisture in Illinois and the European Centre for Medium-Range Weather Forecasts 40-year reanalysis (ERA-40) soil moisture product. Physical mechanisms responsible for the findings are further discussed. This study provides a Northern Hemisphere distribution of the land-atmosphere coupling strength, which can be used to test the model simulations on monthly to seasonal time scales.