Land sensitivity studies towards a potential use of surface sensitive microwave observations over land.
Gérard, É. ; Karbou, F. ; Rabier, F.
<div class="body-text"><br><p><a name="Abstract"><h2>Abstract</h2></a></p><br><p>This paper describes several sensitivity studies carried out<br> with the French global 4-D-Var system to check its ability to <br>assimilate surface-sensitive observations over land from the Special <br>Sensor Microwave Imager (SSM/I). As well as a sound knowledge of <br>land-surface parameters, the assimilation of SSM/I observations requires<br> effective rain-detection and bias-correction algorithms. Three <br>sensitivity components are hence analyzed with a special emphasis on the<br> land-surface emissivity at SSM/I frequencies estimated from satellite <br>observations. Several rain algorithms were tested to reject cloudy/rainy<br> observations over land, and the bias-correction scheme was adapted to <br>improve its performance over land and sea surfaces. Once these problems <br>have been outlined, a global 4-D-Var assimilation experiment which <br>assimilates SSM/I observations over land surfaces was run and compared <br>with a control experiment. The impact on forecast scores has been found <br>to be globally positive. Nevertheless, the very high sensitivity of <br>SSM/I to each of the three components presented in this study is <br>characterized by opposite effects that, once clustered together, lead to<br> some residual biases over land due to their combined effects.</p><br><br></div>
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