Ground-based remote sensing of the atmospheric boundary layer: Assimilating microwave-radiometer and Doppler-lidar observations into the ICON/KENDA system
Authors: Vural Jasmin , Merker Claire , Löffler Moritz , Knist Christine , Kayser Markus , Schomburg Annika 
Published: June 2022

&lt;p&gt;Numerical weather prediction is expected to profit considerably of an improved knowledge of the still underdetermined state of the at&lt;span&gt;mo&lt;/span&gt;&lt;span&gt;s&lt;/span&gt;&lt;span&gt;pheric boundary layer. &lt;/span&gt;&lt;span&gt;As of late, the s&lt;/span&gt;&lt;span&gt;patially and temporally sparse &lt;/span&gt;&lt;span&gt;existing &lt;/span&gt;&lt;span&gt;measurements &lt;/span&gt;&lt;span&gt;of e.g. radiosondes can be complemented &lt;/span&gt;&lt;span&gt;with&lt;/span&gt; &lt;span&gt;wind, temperature, and humidity profiles &lt;/span&gt;&lt;span&gt;of ground-based &lt;/span&gt;&lt;span&gt;remote-sensing &lt;/span&gt;&lt;span&gt;instruments. &lt;/span&gt;&lt;span&gt;The DWD evaluates &lt;/span&gt;&lt;span&gt;several of those instruments &lt;/span&gt;&lt;span&gt;for operational deployment &lt;/span&gt;&lt;span&gt;i&lt;/span&gt;&lt;span&gt;n the framework of the project &amp;#8220;Pilotstation&amp;#8221;. &lt;/span&gt;&lt;span&gt;Her&lt;/span&gt;&lt;span&gt;e, &lt;/span&gt;&lt;span&gt;we&lt;/span&gt;&lt;span&gt; will present the results of assimilating observations of the most mature &lt;/span&gt;&lt;span&gt;of those &lt;/span&gt;&lt;span&gt;systems, &lt;/span&gt;&lt;span&gt;i.e. &lt;/span&gt;&lt;span&gt;microwave radiometer &lt;/span&gt;&lt;span&gt;(MWR) &lt;/span&gt;&lt;span&gt;and Doppler lidar, &lt;/span&gt;&lt;span&gt;into&lt;/span&gt;&lt;span&gt; the &lt;/span&gt;&lt;span&gt;I&lt;/span&gt;&lt;span&gt;CON/KENDA assimilation system &lt;/span&gt;&lt;span&gt;of the DWD&lt;/span&gt;&lt;span&gt;.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;The&lt;/span&gt; &lt;span&gt;MWR&lt;/span&gt; &lt;span&gt;measures&lt;/span&gt;&lt;span&gt; brightness temperatures and thus, the profiles provided by the ICON model have to be transformed to observation space using the forward operator RTTOV-gb. &lt;/span&gt;&lt;span&gt;We ran s&lt;/span&gt;&lt;span&gt;everal assimilation experiments, especially with regard to &lt;/span&gt;&lt;span&gt;the vertical localisation of the MWR channels&lt;/span&gt;&lt;span&gt;.&lt;/span&gt; &lt;span&gt;We will demonstrate how &lt;/span&gt;&lt;span&gt;t&lt;/span&gt;&lt;span&gt;his &lt;/span&gt;&lt;span&gt;localisati&lt;/span&gt;&lt;span&gt;o&lt;/span&gt;&lt;span&gt;n&lt;/span&gt;&lt;span&gt;, &lt;/span&gt;&lt;span&gt;t&lt;/span&gt;&lt;span&gt;ogether with the proper handling of interchannel cross-correlations, &lt;/span&gt; &lt;span&gt;was &lt;/span&gt;&lt;span&gt;key for obtaining &lt;/span&gt;&lt;span&gt;a positive impact on the &lt;/span&gt;&lt;span&gt;upper-air &lt;/span&gt;&lt;span&gt;forecast statistics.&lt;/span&gt;&lt;/p&gt;&lt;p&gt;&lt;span&gt;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.&lt;/span&gt;&lt;/p&gt;