Impact of Skin Temperature Control Variable on the Assimilation of Microwave Temperature-sounding Channels in Regional Numerical Weather Prediction
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Graphical Abstract
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Abstract
Accurate skin temperature is one of the critical factors in successfully assimilating satellite radiance data over land. However, model-simulated skin temperature may not be accurate enough. To address this issue, an extended skin temperature control variable (TSCV) approach is proposed in a variational assimilation framework, which also considers the background error correlation between skin temperature and atmospheric variables. A series of single observation tests and a 10-day cycling assimilation experiment were conducted to evaluate the impact of the TSCV approach on the assimilation of AMSU-A and ATMS (Advanced Technology Microwave Sounder) microwave temperature-sounding channels over land. The results of the single observation tests show that by applying the TSCV approach, not only the direct analysis of skin temperature is realized, but also the interaction between skin temperature and atmospheric variables can be achieved during the assimilation process. The results of the cycling experiment demonstrate that the TSCV approach improves the skin temperature analysis, which in turn reduces the RMSE of the surface variables and low-level air temperature forecasts. The TSCV approach also reduces the difference between the observed and simulated brightness temperatures of both microwave and infrared window channels over land, suggesting that the approach can facilitate the radiance simulation of these channels, thus contributing to the assimilation of window channels.
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