Improved two-metre temperature forecasts in the 2024 upgrade
Amélioration des prévisions de température à deux mètres dans la mise à jour de 2024
Ingleby, Bruce ; Arduini, Gabriele ; Balsamo, Gianpaolo ; Boussetta, Souhail ; Ochi, Kenta ; Pinnington, Ewan ; Rosnay, Patricia de
Two-metre temperature (T2m) is a key forecast variable. Here we describe how changes to ECMWF's Integrated Forecasting System (IFS), which are expected to become operational as part of IFS Cycle 49r1 in 2024, improve short-range forecasts of T2m. Physics changes in IFS Cycle 49r1 will include extensive improvements to surface vegetation fields and changes to make the interpolation of the temperature to 2 m more realistic. There have also been major upgrades to the data assimilation system, which establishes the initial conditions of forecasts (the 'analysis'). Currently, T2m ('screen temperature') and two-metre humidity ('screen humidity') from SYNOP weather station reports and METAR aviation weather reports are assimilated in a separate land surface analysis - primarily to update initial soil moisture and temperature conditions. However, only daytime screen humidity is assimilated in the atmospheric component of the data assimilation system, 4D-Var. In IFS Cycle 49r1, T2m will be assimilated in 4D-Var. This proved beneficial after extensive testing/tuning. Improvements in the separate snow data assimilation system as well as in T2m and soil moisture land data assimilation are also applied. Overall this results in better T2m forecasts, especially in northern hemisphere winter.</p>
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