Proxy Reflectivity Retrieval Of FY-4A Lightning Data And The Evaluation Of Its Impact On Assimilation And Forecasting

As the first Geostationary Satellite with the LMI(Lightning Mapping Imager)instrument aboard,running over the eastern hemisphere,FY-4A(Feng-Yun-4A)can better indicate severe convection and compensate for the limitation of radar observation in temporal and spatial resolution.In order to realize the application of FY-4A lightning data in numerical weather prediction(NWP)models,the main work is as follows:(1)Characteristic analysis of FY-4A lightning data: By comparing FY-4A lightning data with ADTD lightning data,CMORPH precipitation data and Doppler radar reflectivity,the spatial and temporal characteristics of FY-4A lightning data are analyzed.Results indicates that FY-4A lightning data contains more cloud-to-cloud lightning strikes,and can better identify the occurrence and development of convective precipitation.Besides,the time correlation between FY-4A lightning data and radar reflectivity lays a foundation for the retrieval of FY-4A lightning data.(2)3D FY-4A proxy reflectivity retrieval: A logarithmic relationship between FY-4A lightning density and maximum radar reflectivity is presented to convert FY-4A lightning data into maximum FY-4A proxy reflectivity.By the layer-by-layer logarithmic relationship between FY-4A lightning density,and further calculating the real-time profiles of radar reflectivity,the maximum FY-4A proxy reflectivity is extended to 3D FY-4A proxy reflectivity.Results show that the 3D FY-4A proxy reflectivity can better reflect the real-time variance of vertical reflectivity observation.(3)Cycling assimilation and forecast experiments: The 3D FY-4A proxy reflectivity is assimilated in RMAPS-ST to compare with radar assimilation.Four groups of continuous cycling data assimilation and forecasting experiments are carried out for a severe rainfall case.Results demonstrate that,cycling assimilation of3 D FY-4A proxy reflectivity can significantly improve rainfall prediction within 6hours,which is similar to the parallel experiments in assimilating radar reflectivity.In addition,another cycling data assimilation experiments are carried out in mountainous areas without radar data,which further proves that the application of assimilating 3D FY-4A proxy reflectivity can be considered as a useful substitute where the observed radar data are missing.