Assimilation of Cabauw boundary layer observations in an atmospheric single-column model using an ensemble-Kalman filter

Within the Dutch program Climate for Space (KvR) there is a need for monitoring the structure and transport properties of the atmospheric boundary layer (ABL). Boundary layer processes have a direct impact on the human environment. The program specifically asks for improved interpretations of observed trace gas concentrations (KvR-ME2 project). More generally, there is a call for monitoring the full atmospheric column over the Netherland of which the atmospheric boundary layer forms the lowest part (KvR-CS2 project).

At the Cabauw Experimental Site for Atmospheric Research (CESAR) a comprehensive program of atmospheric boundary layer observations is operational. The current project, “Assimilation of Cabauw boundary layer observations in an atmospheric single column model” (ASCAB), aims to give a best estimate of the state of the atmospheric boundary layer at Cabauw by combining these observations with a state of the art atmospheric model. At KNMI, a Regional Atmospheric Climate Model (RACMO) is run in forecast mode on a continuous basis. A Single Column Model (SCM) is directly derived from RACMO. As a method for assimilation of the observations the ensemble Kalman filter (enKF) was selected.

This report describes the operational implementation of the assimilation system. First, a short introduction in data-assimilation techniques is presented, culminating in the presentation of the enKF method. Second, the observations and the SCM will be discussed. Next, the technical implementation of the enKF system in the framework of the SCM is described. Fourth, results of the enKF method will be compared with model runs in which no data assimilation has been applied. Finally some perspectives are sketched.

The enKF system is archived as SCM_enKF.tar.gz and is stored in the Massa Opslag Systeem (MOS). All files that are referred to in this report are included (see Section 7