Improvement of summer precipitation simulation by correcting biases of spring soil moisture in the seasonal frozen-thawing zone over the Northern Hemisphere

Soil moisture (SM) plays an important role in the climate system, and the effects of SM anomalies on climate can persist from month to season. The seasonal frozen-thawing zone (SFTZ) in the northern hemisphere (NH), which is associated with large inter-annual variability in spring SM, is important from land-atmosphere interaction perspective. In this study, by assimilating spring SM in the SFTZ through indirect soil nudging (ISN) in the Weather Research and Forecasting (WRF) model, the effects of correcting spring SM biases in the SFTZ on subsequent summer precipitation simulations in the NH are investigated. The results indicated that correcting spring SM biases in the SFTZ improves the subsequent summer precipitation simulations in the NH. Correcting spring SM biases in the SFTZ significantly adjusts energy and moisture evolution on the land surface from spring to summer. Specifically, the correction of SM biases by assimilating SM in SFTZ in the spring can clearly reduce the biases of sensible heat flux (SH) and latent heat flux (LH) in the summer. This affects land-atmosphere interactions over NH, leading to correcting the negative biases of the geopotential height in the middle troposphere in June and July, as well as larger biases of water vapor transport and its divergence during the summer. The results imply that spring SM in the SFTZ is a potential signal for predicting summer precipitation in the NH.

Automated summary

Soil moisture plays a crucial role in the climate system, and correcting spring soil moisture biases in the seasonal frozen-thawing zone (SFTZ) in the northern hemisphere can improve summer precipitation simulations. This correction significantly adjusts energy and moisture evolution on the land surface, reducing biases in sensible and latent heat fluxes in the summer. Furthermore, it helps correct geopotential height and water vapor transport biases, making spring soil moisture in the SFTZ a potential signal for predicting summer precipitation in the northern hemisphere.