Ground-based remote sensing of the atmospheric boundary layer: Assimilating microwave-radiometer and Doppler-lidar observations into the ICON/KENDA system

Abstract

<p>Numerical weather prediction is expected to profit considerably of an improved knowledge of the still underdetermined state of the at<span>mo</span><span>s</span><span>pheric boundary layer. </span><span>As of late, the s</span><span>patially and temporally sparse </span><span>existing </span><span>measurements </span><span>of e.g. radiosondes can be complemented </span><span>with</span> <span>wind, temperature, and humidity profiles </span><span>of ground-based </span><span>remote-sensing </span><span>instruments. </span><span>The DWD evaluates </span><span>several of those instruments </span><span>for operational deployment </span><span>i</span><span>n the framework of the project “Pilotstation”. </span><span>Her</span><span>e, </span><span>we</span><span> will present the results of assimilating observations of the most mature </span><span>of those </span><span>systems, </span><span>i.e. </span><span>microwave radiometer </span><span>(MWR) </span><span>and Doppler lidar, </span><span>into</span><span> the </span><span>I</span><span>CON/KENDA assimilation system </span><span>of the DWD</span><span>.</span></p><p><span>The</span> <span>MWR</span> <span>measures</span><span> brightness temperatures and thus, the profiles provided by the ICON model have to be transformed to observation space using the forward operator RTTOV-gb. </span><span>We ran s</span><span>everal assimilation experiments, especially with regard to </span><span>the vertical localisation of the MWR channels</span><span>.</span> <span>We will demonstrate how </span><span>t</span><span>his </span><span>localisati</span><span>o</span><span>n</span><span>, </span><span>t</span><span>ogether with the proper handling of interchannel cross-correlations, </span> <span>was </span><span>key for obtaining </span><span>a positive impact on the </span><span>upper-air </span><span>forecast statistics.</span></p><p><span>The Doppler lidar provides horizontal wind measurements, which exhibit a similar quality as the existing radar-wind profiler (RWP) observations and which can be assimilated directly. We will present the results of different assimilation experiments and discuss the impact in comparison with the RWP.</span></p>