Satellite soil moisture data assimilation impacts on modeling weather and ozone in the southeastern US – part I: an overview

Abstract. This study evaluates the impact of satellite soil moisture data assimilation (SM DA) on regional weather and ozone (O3) modeling over the southeastern US during the summer. Satellite SM data are assimilated into the Noah land surface model using an ensemble Kalman filter approach within National Aeronautics and Space Administration's Land Information System framework, which is semicoupled with the Weather Research and Forecasting model with online Chemistry (WRF‐Chem, standard version 3.9.1.1). The SM DA impacts on WRF-Chem performance of weather states and energy fluxes show strong spatiotemporal variability, and many factors such as dense vegetation, complex terrain, and unmodeled water use from human activities may have impacted the effectiveness of the SM DA. The changes in WRF-Chem weather fields due to the SM DA modified various model processes critical to its surface O3 fields, such as biogenic isoprene and soil nitric oxide emissions, photochemical reactions, as well as dry deposition. The SM DA impacted WRF-Chem upper tropospheric O3 partially via altering atmospheric transport and in-situ chemical production of O3 from lightning and other emissions. It is shown that WRF-Chem upper tropospheric O3 response to the SM DA has comparable magnitudes with its response to the estimated US anthropogenic emission changes within two years. As reductions in US anthropogenic emissions would be beneficial for mitigating European O3 pollution, our analysis highlights the important role of SM in quantifying pollutants' transport from the US to Europe. It also emphasizes that using up-to-date anthropogenic emissions is necessary for accurately assessing the SM DA impacts on the model performance of O3 and other pollutants over a broad region. Additionally, this work demonstrates that the SM DA impact on WRF-Chem O3 performance at various altitudes is complicated by not only the model's emission input but also other factors such as the model representation of stratosphere-troposphere exchanges. This work will be followed by a Noah-Multiparameterization (with dynamic vegetation) based study over the southeastern US, in which selected processes including photosynthesis and O3 dry deposition will be the foci.