Impact of Soil Freezing-Thawing Processes on August Rainfall Over Southern China

The impact of soil freezing-thawing processes on August rainfall in Southern China (SC) during 1979-2008 and related physical mechanisms are investigated using the coupled land-atmosphere model Grid-Point Atmospheric Model version 2.0-Community Land Model version 2.0 (GAMIL2.0-CLM2.0). The moisture-budget analysis is employed to quantify the contributions of different factors to the change of precipitation in SC. The results indicate that the vertical moisture advection and its dynamic component play an essential role in the long-term trends of August rainfall. The possible physical mechanism is that the model which includes the supercooled water simulates much higher soil/air temperature in August, especially in the north of 40 degrees N, which is not only weakened the meridional thermal contrast but also induced an anomaly north high-south low circulation pattern in the middle and high latitude of Eurasia. Both resulted in the 200 hPa zonal winds weakening, and 850 hpa northerly wind southward moved. Meanwhile, a convergence anomaly cyclone is initiated in the lower troposphere over SC regions, accompanied by enhanced ascending and strong moisture flux convergence, which is beneficial to the increased precipitation. This study provides a new interpretation of the southern flooding during 1979-2008 from the point of frozen soil changing.

Automated summary

This study investigates the impact of soil freezing-thawing processes on August rainfall in Southern China using a coupled land-atmosphere model. The results suggest that vertical moisture advection and its dynamic component play a crucial role in the long-term trends of August rainfall.