Deriving Atmospheric Motion Vectors In Cloud-free Regions Around Typhoon From FY-2E IR Imagery And Cases Study

For their excellent temporal and spatial coverage, Atmospheric motion vectors(AMVs) have dispalyed great application perspective in the tropical cyclone track forecasting and improving the initial fields and numerical forcasts. In Geostationary Opertional Meteorological Satellite FY-2E infrared imagery, AMVs in cloud-free regions have been retrieved by the time difference technique.can which supply for the wind field in ocean, desert regions and so on.Around the typhoon "HAIKUI","SAOLA" and "MEARI", using the clear air ventilation technology based on the time difference technique, this paper, the typhoon and the clear zone around the wind vector inversion example analysis, the work is mainly carry out from the selection of tracer, the computation of wind field in cloud-free areas height assignment of the AMVs in cloud-free regions, the application of the wind vector in ropical cyclone track forecasting:By using MODTRAN radiation transfer model that is combining with the spectral response function of FY-2E space-borne radiometers split window channels, this paper simulated the sensitivity between the split window brightness temperature with the atmospheric water vapor and aerosol in the tropical cloud-free atmosphere,and the sensitivity equation between bright temperature with atmospheric water vapor and aerosols is calculated.Then, combined with the feature of FY-2e temperature sensitivity and the techniques for deriving AMVs with satellite images, we calculated the existence conditions of these two weak tracer signal with different temperature sensitivity. At last, using Atmosphere Total Precipitation Water content product in2010and2011, The characteristics of atmospheric water vapor distribution in China is given out.The result show that in the tropical atmosphere mode, the brightness temperature changes in the cloud-free over ocean area was caused by the variation of water vapor, due to the aerosol contents don’t meet the above requirements, brightness temperature texture feature over the ocean is mainly caused by changes in atmospheric water vapor content.so in the tropical ocean the tracer signal for deriving AMVs is atmospheric water vapor content. And statistical result of the atmospheric water vapor in cloud-free areas shows at least more than40%of atmospheric water vapor can be tracked as tracer.In view of the height assignment methods of data in cloud-free regions,which is retrieved by the time difference technique, is relatively easy, the height assignment methods that is using the standard profile to compute weight response between Water vapor content and Satellite Infrared Radiation at different heights is refined.first, the standard profile is replaced by the practical atmospheric profile when the methods is employed to adjust the heights of AMVs data in cloud-free regions.so the height of the wind vector is closer to the actual situation, Then the height adjustment method is used for AMVs data in cloud-free regions above.To explore the precision of the wind vector in cloud-free regions after height assignment, statistic results of AMVs’heights distribution with three typhoon case show that the typhoon around the sky, the wind vector are mainly distributed in the atmosphere of the underlying between600～900hpa. statistical test and error analysis to AMVs in cloud-free regions is compared before and after height adjustment for three typhoon cases.by using the method of point by point near layer the Root-Mean-Square Errors、the blas and Standard Deviation U, Vwind component is calculated respectively between NCEP wind field data and wind vector in cloud-free areas. Analysis shows that after height assignment, the root mean square and the standard deviation of each level’s wind vector in cloud-free areas is decreased obviously, especially the errors and precision of wind vector between600～800hPa have obvious improvement.To verify the quality of AMVs data in cloud-free regions based on the time difference technique the Sensitivity experiments is performed in the three-dimensional meso-scale assimilation model WRF-3DVAR. The assimilation experimen is designed with three groups of numerical experiment scheme for three typhoon cases. The result of assimilation experiments confirm that the forcast track error of Typhoon is reduced in48hours with the assimilation of AMVs in cloud-free regions. Therefore this height assignment can improve the quality of AMVs in cloud-free regions.