A numerical study on the impact of soil freezing on the continental-scale seasonal cycle

The thermal and hydrological impacts of soil freezing on the climate system are studied using an atmospheric general circulation model. The difference between runs with and without soil freezing, i.e., including and excluding the latent heat of fusion and the impermeability of frozen soil, shows that the inclusion of soil freezing leads to higher surface temperature in middle and high latitudes over land in summer. This leads to larger water vapor flux and precipitation in Southeast Asia. The higher temperature over land in summer results from lower evaporation caused by lower surface soil moisture. The low surface soil moisture is caused by additional runoff of snowmelt in spring due to the impermeability of frozen soil and low soil liquid water due to underlying frozen ground. Precipitation is lower in the middle of the Eurasian and North American Continents due to the lower evaporation. The sensitivity of temperature change to soil moisture change is high in regions where potential evaporation is high. In winter, deep soil temperature is higher with soil freezing in frozen ground regions due to the latent heat of freezing, but the surface temperature difference is governed more by atmospheric dynamical responses. The signs of the impacts are found to be the same in one-dimensional experiments with various hydrological schemes and parameters.