Two sets of assimilation experiments on a landfalling typhoon--Typhoon Dan （1999） over the western North Pacific were designed to compare the performances of two kinds of variational data assimilation schemes that a...Two sets of assimilation experiments on a landfalling typhoon--Typhoon Dan （1999） over the western North Pacific were designed to compare the performances of two kinds of variational data assimilation schemes that are the 3-Dimensional Variational data assimilation of Mapped observation （3DVM） and the 4-dimensional variational data assimilation （4DVar）. Results show that： （1） both the 3DVM and 4DVar successfully improved the simulations of typhoon intensity and track incorporating the satellite AMSU-A retrieved temperature and wind data into the initial conditions, and the 3DVM more significantly due to the flow-dependent of background error covariance matrix and observation error covariance matrix like 3- dimensional variational data assimilation （3DVar） circle; （2） inclusions of extra model integration iterations at each observation time in the 3DVM make it more consistent with prediction model; （3） the 3DVM is much more time-saving due to the exclusion of the adjoint technique in it.展开更多
In this study, an extension of the TREC （Tracking Radar Echo by Correlations） technique, named Tropical Cyclone （TC） circulation TREC （T-TREC）, is developed to retrieve the winds of landfalling typhoons in China...In this study, an extension of the TREC （Tracking Radar Echo by Correlations） technique, named Tropical Cyclone （TC） circulation TREC （T-TREC）, is developed to retrieve the winds of landfalling typhoons in China. The T-TREC analysis is performed on a polar grid centered at the TC center, using arc-shaped correlation cells and an arc-shaped search area. The search for the best correlation match is confined along the cyclonic direction with a limited search distance in the radial direction based on the cyclonic circulation characteristics of TCs in the Northern Hemisphere. The TC center is determined objectively using reflectivity data while the Doppler radar radial velocities are incorporated to estimate the search range and create a velocity correlation matrix as auxiliary constraints. The T-TREC was applied to the landfalling Typhoon Saomai （0608） observed by Chinese next generation Weather Surveillance Radar 1998 Doppler （CINRAD WSR-98D） on the southeast coast of China. The results show that the T-TREC has the ability to estimate the typhoon circulation with an average bias of 4 m s -1 . The incorporation of radial velocity data could distinctively improve wind retrievals for intense typhoons, especially by reducing the underestimation caused by fairly uniform reflectivity patterns in the vicinity of the eyewall and the outer rainband. A quantitative evaluation of the influence of typhoon center and cell size on the wind estimation demonstrates that the quality of the T-TREC retrieved wind circulation depends on the estimation of the typhoon center. A 4-km deviation of the TC center may result in a 10% increase in the retrieved wind error. The effect of cell size depends on the typhoon scale： better wind retrieval results can be obtained for a smaller typhoon.展开更多
文摘Two sets of assimilation experiments on a landfalling typhoon--Typhoon Dan （1999） over the western North Pacific were designed to compare the performances of two kinds of variational data assimilation schemes that are the 3-Dimensional Variational data assimilation of Mapped observation （3DVM） and the 4-dimensional variational data assimilation （4DVar）. Results show that： （1） both the 3DVM and 4DVar successfully improved the simulations of typhoon intensity and track incorporating the satellite AMSU-A retrieved temperature and wind data into the initial conditions, and the 3DVM more significantly due to the flow-dependent of background error covariance matrix and observation error covariance matrix like 3- dimensional variational data assimilation （3DVar） circle; （2） inclusions of extra model integration iterations at each observation time in the 3DVM make it more consistent with prediction model; （3） the 3DVM is much more time-saving due to the exclusion of the adjoint technique in it.
基金Supported by the "973" National Key Basic Research Program of China under Grant No. 2009CB421502the National Natural Science Foundation of China under Grant Nos. 40505004, 40333025, and 40975011
文摘In this study, an extension of the TREC （Tracking Radar Echo by Correlations） technique, named Tropical Cyclone （TC） circulation TREC （T-TREC）, is developed to retrieve the winds of landfalling typhoons in China. The T-TREC analysis is performed on a polar grid centered at the TC center, using arc-shaped correlation cells and an arc-shaped search area. The search for the best correlation match is confined along the cyclonic direction with a limited search distance in the radial direction based on the cyclonic circulation characteristics of TCs in the Northern Hemisphere. The TC center is determined objectively using reflectivity data while the Doppler radar radial velocities are incorporated to estimate the search range and create a velocity correlation matrix as auxiliary constraints. The T-TREC was applied to the landfalling Typhoon Saomai （0608） observed by Chinese next generation Weather Surveillance Radar 1998 Doppler （CINRAD WSR-98D） on the southeast coast of China. The results show that the T-TREC has the ability to estimate the typhoon circulation with an average bias of 4 m s -1 . The incorporation of radial velocity data could distinctively improve wind retrievals for intense typhoons, especially by reducing the underestimation caused by fairly uniform reflectivity patterns in the vicinity of the eyewall and the outer rainband. A quantitative evaluation of the influence of typhoon center and cell size on the wind estimation demonstrates that the quality of the T-TREC retrieved wind circulation depends on the estimation of the typhoon center. A 4-km deviation of the TC center may result in a 10% increase in the retrieved wind error. The effect of cell size depends on the typhoon scale： better wind retrieval results can be obtained for a smaller typhoon.
