Assimilating the SCATSAR-SWI with SURFEX for a high-resolution European soil moisture product

Due to manifold land-atmosphere interactions, soil moisture is an essential part of the energy-water cycle. Especially when the incoming solar radiation is high, large effects of soil moisture onto the lower atmosphere can be expected. In addition, the knowledge of large-scale soil moisture fields is important for other applications, e.g., in hydrology and agriculture. Remotely sensed soil moisture products provide information on global scales, continuously yielding better quality as well as higher spatial and temporal resolution. The ingestion into data assimilation systems propagates the obtained information in time and – via subsequent modelling – onto other physical variables.

By the assimilation of a high-resolution soil moisture product, we aim to develop a high-level soil-moisture product for Europe and to provide an improved surface initialisation for the NWP model AROME. Our focus is on fully exploiting the high spatial resolution (1 km) of the multi-layer fused soil-moisture product SCATSAR-SWI. For assimilation, we use the surface model SURFEX, which employs a simplified Extended Kalman Filter and the multi-layer diffusion scheme ISBA-DIF. We ran the assimilation system on different resolutions and found an improvement of the forecast metrics of the 2 m temperature and 2m relative humidity using higher resolution systems. In addition, we use the water balance as a reference measure for a domain-covering verification of the soil moisture analysis.