Evaluating the performance of SURFEXv5 as a new land surface scheme for the ALADINcy36 and ALARO-0 models

Abstract

Abstract. The newly developed land surface scheme SURFEX (Surface Externalisée) is implemented into a limited area numerical weather prediction model running operationally in a number of countries of the ALADIN and HIRLAM consortia. The primary question addressed is the ability of SURFEX to be used as a new land surface scheme and thus assessing its potential use in an operational configuration instead of the original ISBA (Interactions between Soil, Biosphere, and Atmosphere) scheme. The results show that the introduction of SURFEX either gives improvements or neutral impact on the 2 m temperature, 2 m relative humidity, and 10 m wind. However, it seems that SURFEX has a tendency to produce higher maximum temperatures at high elevation stations during winter daytime which degrades the scores. In addition, surface radiative and energy fluxes improve compared to observations from the Cabauw tower. The results also show that promising improvements with a demonstrated positive impact are achieved by introducing the Town Energy Balance (TEB) scheme. It was found that the use of SURFEX has a neutral impact on the precipitation scores. However, the implementation of TEB within SURFEX for a high resolution run tends to cause rainfall to be locally concentrated and the total accumulated precipitation decreases obviously during the summer. One of the novel features developed in SURFEX is the availability of a more advanced surface data assimilation using the Extended Kalman Filter. The results over Belgium show that the forecast scores are similar between the Extended Kalman Filter and the classical Optimal Interpolation scheme. Finally, concerning the upper air scores, the introduction of SURFEX either gives improvement or neutral impact in the free atmosphere.