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云参数对RTTOV5模式模拟误差的影响分析
THE IMPACT OF CLOUD PARAMETERS ON THE SIMULATED ERRORS IN RTTOV5
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摘要: 该文根据1998年8月的业务TOVS反演的温度、水汽垂直廓线资料以及其它资料, 利用RTTOV5模式模拟NOAA14极轨气象卫星上相应红外探测 (HIRS) 通道的辐射亮温值, 将模拟值对比实测TOVS探测资料, 结果表明, 晴空模式模拟亮温与实测值的误差小于部分有云时的误差, 模拟误差受云的影响呈反相变化, 对水汽敏感的中低层探测通道在晴空时的误差小于部分有云情况; 通过对比白天和夜间短波窗区探测通道模拟误差, 分析了其受地面反射太阳光辐射的影响的大小及其原因所在; 并利用RTTOV5的伴随模式和Jacobine模式分析了模式模拟误差对初始场云参数的敏感性。该研究为TOVS/ATOVS探测资料在3DR或4DR变分同化中的直接应用奠定了基础。Abstract: TOVS/ATOVS data from meteorologic satellite can provide the vertical distribution of temperature and humidity in the atmosphere. In order to use these data in NWP models directly, then to make the initial field of NWP model more accurate and improve forecast finally, a fast transmittance model (RT model) is required in a multi-dimensional data variational assimilation system. There will be big errors while simulating HIRS data by an RT model, because HIRS data in TOVS/ATOVS can not get the information of the vertical distribution of temperature and humidity below the clouds. Before assimilating TOVS/ATOVS data into NWP model, it is a necessary task to analyze the impact of the cloud parameters (the top of cloud and cloud fraction are included mainly) on simulated errors using RTTOV5, based on the actuality of operational TOVS data every day (about 70% observation points are partly cloudy).The temperature and humidity profiles from operational TOVS data, as well as some others data necessary to run RTTOV5, are used to compute the brightness temperature with respect to HIRS channels in NOAA14. Then the impact of the cloud fraction and the top of cloud on simulated errors in models are estimated. Finally an adjoint model and a Jacobine model of RTTOV5 are used to analyze the sensitivity of the simulated errors of RTTOV5 to initial cloud parameters (the cloud fraction and the pressure of of cloud top).
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表 1 RTTOV5初始输入变量
表 2 NOAA-14 HIRS-2光谱通道特征及其主要探测目的
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[1] Pailleux J.Design of a variational analysis:organization and main scientific points.ECMWF Tech.Mem.150, 1989. [2] Pailleux J.A global variational assimilation scheme and its application for using TOVS radiances.Preprints of WMO Int.Symp.On Assimilation of Observations in Meteorology and Oceanography, Clermont-Ferrand, France, July 1990.325~328. [3] Eyre J R.Progress on direct use of satellite sounding radiances in numerical weather prediction.Preprints of WMO Int.Symp.On Assimilation of Observations in Meteorology and Oceanography, Clermont-Ferrand, France, July 1990.117~121. [4] Saunders R, Matrecardi M, Brunel P.A fast radiative transfer model for assimilation of satellite radiance observations———RTTOV5.Research Department Technical Memorandum No.282, Aug.1999. [5] Erye J R.Inversion of cloudy satellite sounding radiances by nonlinear optimal estimation.Q.J.R.Meteor.Soc., 1989, 115: 1001~1037. doi: 10.1002/(ISSN)1477-870X -
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