Christoph Schraff, Deutscher Wetterdienst
Towards an operational use of the Kilometre-scale Ensemble Data Assimilation (KENDA) at DWD
Coauthors
Hendrik Reich, Andreas Rhodin, Roland Potthast, Klaus StephanAbstract:
An ensemble Kalman filter for kilometre-scale or convective-scale data assimilation (KENDA) has been developed for the COSMO model. The KENDA system is built up of a local ensemble transform Kalman filter (LETKF) including a deterministic analysis based on the Kalman gain for the analysis ensemble mean. The KENDA software suite includes tools for adaptive localization, multiplicative and additive covariance inflation, relaxation to prior perturbations, as well as adaptive observation errors.
In pre-operational trials at the German Weather Service (DWD) and related previous tests, e.g. for a 28-day convective summer period, conventional observations (radiosonde, aircraft, wind profiler, surface station data) are assimilated. In addition, latent heat nudging for the use of radar-derived precipitation has been incorporated into the KENDA assimilation cycle. This is compared to the current operational data assimilation scheme for the COSMO model, which uses the same observations and is based on observation nudging complemented by latent heat nudging. The quality of the deterministic forecasts from the KENDA system is overall superior to that of the nudging-based system in the tests. Various system components were been investigated, including the impact of the latent heat nudging incorporated in the LETKF assimilation cycle. We will focus on presenting some of the main results from these tests.
Apart from the aim to replace the nudging for the operational deterministic forecasts, another purpose of the KENDA system is to improve the initial conditions of the operational ensemble prediction system COSMO-DE-EPS. Furthermore, we will also give a brief overview of ongoing projects that deal with additional, high-resolution observation data such as 3-dimensional radar reflectivity and radial velocity, GNSS slant path delay, and cloudy SEVIRI radiances in view of their future operational use in the KENDA system.