Research On Identification And Data Assimilation Of Target Observation Sensitive Areas For Offshore Typhoon Forecasting In My Country

The target observation method is to increase the observation in the sensitive area to improve the quality of the initial field,and then to improve the accuracy of the existing numerical model forecast.As a cuttingedge scientific problem in the field of numerical prediction,it has been widely used in the study of highimpact weather.The Ensemble Transform Kalman Filter(ETKF)target observation method has shown certain advantages in various target observation methods due to its low calculation cost and flow-dependent properties.It has been applied to typhoons,extratropical cyclones,mid-latitude heavy precipitation and freezing rain.Using the ETKF target observation method,this article first discusses the key factors affecting the variance of the target observation signal based on the analysis of typhoon cases.Focusing on my country's landing typhoons in the South China Sea in the past 10 years,based on the classification results of typhoon path differences,the climatological characteristics of different types of typhoon observation sensitive areas in the South China Sea are studied.Then try to design a fixed observation sensitive area distribution with climate significance,and provide a scientific basis for the observing system configuration of the target sensitive area.The main conclusions are as follows:(1)When identifying the sensitive area of the typhoon system,the number of members of the ensemble forecast data used by the ETKF target observing system and the forecast time effect will affect the system's ability to describe the model forecast error covariance matrix,and thus the final identification result of the sensitive area is intended.At the same time,there are differences in the distribution of signals in the sensitive area under each level,and the ETKF system has a higher degree of response to the meteorological elements at 925 hPa and 500 hPa.The large value of the sensitive area signal often appears in the strong wind shear area,but the strong wind shear area is not necessarily the strong observation sensitive area.(2)The sensitive area of CHAN-HOM(1509)is mainly concentrated in the area between the typhoon center and Subtropical high.Subsequent simulated observation sensitivity experiments show that the introduction of additional target observation data can effectively improve the quality of route forecasting,but the improvement of precipitation forecast quality is not significant.The ETKF system has recognition effect on the sensitive area of CHAN-HOM observation.(3)Research on the classification of landing typhoons in Guangdong shows that the ETKF target observation system has a certain recognition ability for northern,central,and southern typhoon.Among them,the northern and central types of case target observation key areas appear in the waters north of the Philippines,and the southern type cases appear in the South China Sea.Through synthetic analysis and research,it is found that the strongest sensitive area signal of each type of case has a good corresponding relationship with the nearby center of maximum wind speed.In terms of the economic benefits of implementing target observations,climatological observation sensitive areas of typed typhoons can replace real-time typhoon target observations.