Role of Soil Moisture on the Earth’s Radiative Balance through Modulations of Dust Radiative Forcing

Dust is an abundant atmospheric aerosol that contributes to direct and indirect aerosol effects. The abundance of dust emissions depends on soil composition and factors responsible for dust mobilization. Wind speed and soil moisture are probably the most important factors. The wind is responsible for lifting soil particles from the ground, while the soil moisture increases the cohesive forces of the soil particles. The influence that soil moisture exerts on dust emissions modulates the dust–aerosol impacts on the Earth’s radiative balance. How important these soil moisture modulations are is unknown.

To quantify the magnitude of the soil moisture modulations, we have conducted a series of multi-year numerical simulations with the Weather Research and Forecasting (WRF) model coupled with chemistry (WRF-Chem) covering the Contiguous U.S. (CONUS) at 9-km grid spacing. CONUS has important dust sources and dense in situ instrumentation. Soil moisture retrievals from the Soil Moisture Active Passive (SMAP) satellite are assimilated to reduce a wet soil moisture bias in the western U.S., where the most important dust sources are located. After ensuring agreement between the in situ observations and aerosol load, the impacts of soil moisture are examined by introducing positive/negative soil moisture anomalies in the dust emissions using additional WRF-Chem simulations. In this presentation we will summarize our findings characterizing the impacts of soil moisture in the top-of-the-atmosphere and surface radiative forcing (shortwave, longwave, and net radiation) through modulations of dust emissions that could introduce non-trivial impacts in the radiative balance (~10%) in this clear connection between the hydrological and energy cycles.