Simulation And Assimilation Of Fengyun-3 Microwave Humidity Sounder Data In Typhoon Precipitation Cloud Regions

The observation of space-borne microwave remote sensing instruments in cloud and precipitation region involves the key atmospheric information related to the thermodynamic and dynamic processes of weather systems,which is of great potential in improving the accuracy of disastrous weather forecast.Therefore,in the past decade,the numerical forecasting centers all over the world have gradually carried out the research on assimilation of microwave data in cloud and precipitation regions.The demand of the numerical weather prediction model independently developed by China for observation information in cloud and precipitation regions is increasingly urgent.Due to the existing problems of inaccurate radiative transfer calculation and imperfect assimilation technology scheme in cloud precipitation regions,assimilation of the data of microwave sounders in cloud and precipitation regions is a hot topic in the international academic circles.The assimilation is more challenging especially in tropical convective precipitation cloud regions with solid hydrometeor.This paper studies the assimilation of Fengyun-3 Microwave Humidity Sounder(MWHS)data in typhoon precipitation cloud regions.The progress and conclusions are given as follows:(1)MWHS all-weather observation simulation model is established and evaluated by using observation simulation deviation analysis,vertical cross-section analysis and brightness temperature probability density distribution analysis.By making comparative verification with the global model of the European Centre for Medium-range Weather Forecasts,the scattering effect of the hydrometeor in allweather simulation is found to be underestimated in the simulation.Compared with the global model,the regional model has more serious problem of forecast cloud dislocation.At present,there are few quantitative evaluations on the observation information of MWHS channels,especially the 118 GHz channel in both domestic and foreign researches.This paper studies the problem by using two methods: using the Jacobean matrix method to calculate the sensitivity and sensitive altitude of each channel to hydrometeor and using the degree of freedom reduction method to quantitatively evaluate the atmospheric and cloud information of each channel in typhoon convective precipitation cloud region.The result show that the main information observed through 118 GHz and 183 GHz frequency bands in the typhoon precipitation cloud regions comes from snow particles,accounting for 98.2% and 76.8%of the total wet atmospheric information content.As 118 GHz frequency band has lower detection altitude and more channels,more snow information can be obtained through118 GHz band than 183 GHz band.(2)In order to improve the accuracy of the all-weather simulation,the calculation scheme of snow particle scattering in radiative transfer model has been improved.The cloud dislocation of numerical model is a key factor that affects the calculation of allweather observation-simulation deviation.This paper presents a new method based on active and passive joint observation.The deviation of the active and passive joint observation-simulation can reduce the impact of cloud dislocation and be used to accurately evaluate the simulation effect of different non-spherical scattering calculation schemes.We have established the single-shaped scattering schemes suitable for MWHS in typhoon region,including the scattering schemes of large block aggregate and plate type,etc.The deviation of the active and passive joint observation-simulation calculated with the best large block aggregate scheme is reduced from-16.52 K of the spherical shaped scheme to 1.09 K,the mean square root error is reduced from 26.74 K to 19.03 K.By using the constrained least square method,we have statistically calculated the weights of the different shaped schemes in the ensemble scattering scheme of non-spherical particles and established the non-spherical particles ensemble scattering scheme.The average deviation of the ensemble scattering scheme is-0.07 K and the mean square root error is 12.68 K.Through verification in all-weather simulation of several typhoon scenarios,the ensemble scattering scheme of nonspherical particles can effectively reduce the problem of low scattering effect of solid hydrometeor in all-weather simulation compared to the spherical Mie scattering scheme,which has improved the distribution skewness and bias of observation-simulation deviation,making the distribution closer to Gaussian unbiased distribution.The distribution skewness of channel 9 was improved from 0.34 to 0.28,and from 0.51 to0.47 for channel 15.The distribution bias of channel 9 was improved from-3.34 K to-3.03 K,and from-6.77 K to-5.15 K for channel 15.(3)The traditional one-dimensional Bayesian inversion approach plus the scheme of 3D variational assimilation of total water vapor is no longer applicable to typhoon region.An improved method is given in this paper,and the scheme of total amount of water vapor in assimilation cloud precipitation region is replaced by solid water condensate observed by MWHS.Based on the improved radiative transfer scattering scheme,solid state hydrometeor in typhoon precipitation cloud region is inverted by Bayesian approach.Through coupling the hydrometeor observation operator in the assimilation model,the variational assimilation of MWHS data in typhoon precipitation cloud region is realized.The assimilation results of typhoon cases show that the improved one-dimensional Bayesian plus 3D variational assimilation of hydrometeor can significantly improve the simulation of typhoon wind field structure and maximum wind speed by affecting the temperature,humidity and wind field of the initial field.At the same time,the distribution of spiral structure of typhoon precipitation cloud is improved.