Impact of the Assimilation of Metop-B Satellite Refractivity Profiles in the Forecasts of the CPTEC/INPE During the Months of January and August 2014

Abstract Currently, there is an increase in the number of low orbit satellites dedicated to radio occultation of GPS signals. The MetOp-B is one of these new satellites, but it has not been explored in the data assimilation performed in Brazil. In order to include this source of observation in the database used in the assimilation of the CPTEC/INPE and evaluate its impact in the performance of the Atmospheric Global Circulation Model used operationally at the center, an experiment with data from January and August 2014 was executed. The results were compared with another experiment without assimilating those data, which showed that the inclusion of the MetOp-B refractivity profiles, has impacted beneficially the assimilation of more data from the other satellites in use, such as COSMIC, TerraSAR-X and MetOp-A. The most prominent results were observed in August, with root mean squared gain values greater than 40% in the state variables for the 24-h forecast over the Southern Hemisphere, variables that are directly related to the refractivity values. Beyond that, the anomaly correlation coefficient values over South America indicated that, adding the MetOp-B data, the zonal and meridional wind components at 250 hPa were indirectly impacted, showing the importance of assimilate such data.

摘要 当前，致力于GPS信号无线电掩星（radio occultation）观测的低轨卫星（low orbit satellites）数量持续增长。MetOp-B便是这类新型卫星之一，但巴西境内开展的数据同化（data assimilation）研究尚未对其展开相关探索。为将该观测数据源纳入巴西气候预测与气候研究中心（CPTEC）与巴西国家空间研究所（INPE）所用的同化数据库，并评估其对该中心业务运行的全球大气环流模式（Atmospheric Global Circulation Model）性能的影响，本研究基于2014年1月与8月的观测数据实施了同化试验。将本次试验结果与未同化该类观测数据的对照试验结果进行对比后发现，同化MetOp-B的折射率廓线（refractivity profiles），可对当前在用的其他卫星（如COSMIC、TerraSAR-X及MetOp-A）的观测数据同化产生有益的促进效果。试验效果在8月最为显著：南半球区域24小时预报的状态变量（state variables）中，均方根增益（root mean squared gain）值均超过40%，而这些状态变量与折射率数值直接相关。此外，南美洲区域的距平相关系数（anomaly correlation coefficient）结果显示，加入MetOp-B观测数据后，250百帕高度层的纬向风分量与经向风分量（zonal and meridional wind components）亦得到间接改善，印证了同化该类观测数据的重要价值。