Modelling the Asian summer monsoon rainfall and Eurasian winter/spring snow mass

Abstract The interannual variation of the south Asian summer monsoon is analysed based on sets of present day climate simulations using the UK Universities' Global Atmospheric Modelling Programme (UGAMP) generalcirculation model with different land surface parametrization schemes, different horizontal resolutions, and sea surface temperature variations. Generally, a negative relationship is found between south Eurasian winter/spring snow mass and the amount of summer monsoon rainfall over India in all simulations. However, the significance of this relationship is dependent on the land surface parametrization scheme. The simulations using the no‐flux boundary condition at the bottom of a three‐layer soil model give a strong negative correlation. This inverse relationship is the strongest over north India and the foothills of the Himalayas and is statistically significant. The model results are in good agreement with observational studies. Composite analyses suggest that less winter/spring snowfall over south Eurasia is associated with a strong Indian summer monsoon, characterized by strong south‐westerlies over the Arabian Sea in the lower troposphere in the June‐August season and heavy precipitation in early summer over north India and the foothills of the Himalayas. In contrast, heavy winter/spring snowfall delays the onset of the Indian summer monsoon through the feedback of snowmelt, soil moisture and evaporation processes, and is associated with weak summer precipitation over the two regions. Sensitivity studies confirm that the snow mass‐Indian monsoon relationship identified in the simulation at T42 is also robust in the simulation at T31. However, a negative relationship does not exist in the simulation at T21, indicating the importance of horizontal resolution in maintaining the snow‐monsoon relationship in the UGAMP model.