IMPACT OF DATA ASSIMILATION FOR THE IASI OBSERVATIONS ON THE FORECAST OF TYOHOON HONGXIA AND MOLANDI

YU Yi; ZHANG Wei-min; CAO Xiao-qun; ZHAO Yan-lai; DUAN Bo-heng

doi:10.16032/j.issn.1004-4965.2017.04.007

Abstract：The Infrared Atmospheric Sounder Interferometer (IASI) provides the temperature and humidity information with high precision about the atmosphere in the vertical direction.The IASI instrument can detect the characteristics of typhoon structure and make up for the shortage of the observation data distributed sparsely in typhoon-affected areas.In this study,a three-dimensional variational data assimilation for Weather Research and Forecasts (WRFDA) system was chosen as the basic assimilation system,and the MW cloud detection put forward by McNally was implemented in the WRFDA system for IASI cloud contamination detection and the cloud parameters were tuned for the research.All the IASI observations are assimilated after quality control and variational bias correction and the impact of the data assimilation on the forecasts of the super typhoon Hongxia (1506) and Molandi (1614) are assessed.The results from both the typhoon experiments are similar and indicate that the cloud detection influences the assimilation of the IASI observations very much.For the super typhoon Hongxia,the MW cloud detection scheme retained just 16.2％ the number of observations by the large-threshold LMW cloud detection scheme and 9.2％ of that by the MMR cloud detection scheme for the upper-level channel 299,and 3.3％ and 2.6％ respectively for the lower-level channel 921,but the analysis affected by the MW cloud detection scheme reduces the track error of typhoon Hongxia for the first 72 hours most remarkably and improves the path forecast most accurately.Generally the assimilation of IASI observations improves the skills of typhoon forecast.