The purpose of this study is to investigate the effectiveness of two different ensemble forecasting （EF） techniques-the lagged-averaged forecast （LAF） and the breeding of growing modes （BGM）. In the BGM experime...The purpose of this study is to investigate the effectiveness of two different ensemble forecasting （EF） techniques-the lagged-averaged forecast （LAF） and the breeding of growing modes （BGM）. In the BGM experiments, the vortex and the environment are perturbed separately （named BGMV and BGME）. Tropical cyclone （TC） motions in two difficult situations are studied： a large vortex interacting with its environment, and an apparent binary interaction. The former is Typhoon Yancy and the latter involves Typhoon Ed and super Typhoon Flo, all occurring during the Tropical Cyclone Motion Experiment TCM- 90. The model used is the baroclinic model of the University of New South Wales. The lateral boundary tendencies are computed from atmospheric analysis data. Only the relative skill of the ensemble forecast mean over the control run is used to evaluate the effectiveness of the EF methods, although the EF technique is also usecl to quantify forecast uncertainty in some studies. In the case of Yancy, the ensemble mean forecasts of each of the three methodologies are better than that of the control, with LAF being the best. The mean track of the LAF is close to the best track, and it predicts landfall over Taiwan. The improvements in LAF and the full BGM where both the environment and vortex are perturbed suggest the importance of combining the perturbation of the vortex and environment when the interaction between the two is appreciable. In the binary interaction case of Ed and Flo, the forecasts of Ed appear to be insensitive to perturbations of the environment and/or the vortex, which apparently results from erroneous forecasts by the model of the interaction between the subtropical ridge and Ed, as well as from the interaction between the two typhoons, thus reducing the effectiveness of the EF technique. This conclusion is reached through sensitivity experiments on the domain of the model and by adding or eliminating certain features in the model atmosphere. Nevertheless, the forecast tracks in some of the cases are improved over that of the control. On the other hand, the EF technique has little impact on the forecasts of Flo because the control forecast is already very close to the best track. The study provides a basis for the. future development of the EF technique. The limitations of this study are also addressed. For example, the above results are based on a small sample, and the study is actually a simulation, which is different than operational forecasting. Further tests of these EF techniques are proposed.展开更多
Ensemble forecasting of tropical cyclone (TC) motion was studied using a primitive equation barotropic model by perturbing initial position and structure for 1979 1993 TC. The results show that TC initial position per...Ensemble forecasting of tropical cyclone (TC) motion was studied using a primitive equation barotropic model by perturbing initial position and structure for 1979 1993 TC. The results show that TC initial position perturbation affects its track, but the ensemble mean is close to control forecast. Experiments was also performed by perturbing TC initial parameters which were used to generate TC initial field, and more improvement can be obtained by taking ensemble mean of selective member than selecting members randomly. The skill of 60 % 70 % of all cases is improved in selective ensemble mean. When the ambient steering current is weak, more improvement can be obtained over the control forecast.展开更多
The interaction between tropical cyclone(TC)and the large-scale mean flows such as the inter-tropical convergence zone(ITCZ)is investigated using a three-dimensional primitive equation model.Once a TC develops in the ...The interaction between tropical cyclone(TC)and the large-scale mean flows such as the inter-tropical convergence zone(ITCZ)is investigated using a three-dimensional primitive equation model.Once a TC develops in the vicinity of the ITCZ region where satisfies both barotropic and baroclinic instabilities,the southeastward energy dispersion from the TC may disturb the ITCZ and thus help its breakdown.Cumulus convection can be organized in the region of cyclonic circulation,and the interaction between convective heating and the perturbation circulation may enhance the development of the waves,leading to the generation of a new tropical cyclone to the east.While the TC moves to the high latitude,the ITCZ will reform.Though repeating of this process,a synoptic-scale wave train oriented in the northwest-southeast direction can be generated and self-maintained.The results suggest that the mutual interaction among the low-frequency background flow,wave train pattern and TCs provides a possible mechanism for the origin of the summer synoptic scale wave train pattern over the western North Pacific.展开更多
文摘The purpose of this study is to investigate the effectiveness of two different ensemble forecasting （EF） techniques-the lagged-averaged forecast （LAF） and the breeding of growing modes （BGM）. In the BGM experiments, the vortex and the environment are perturbed separately （named BGMV and BGME）. Tropical cyclone （TC） motions in two difficult situations are studied： a large vortex interacting with its environment, and an apparent binary interaction. The former is Typhoon Yancy and the latter involves Typhoon Ed and super Typhoon Flo, all occurring during the Tropical Cyclone Motion Experiment TCM- 90. The model used is the baroclinic model of the University of New South Wales. The lateral boundary tendencies are computed from atmospheric analysis data. Only the relative skill of the ensemble forecast mean over the control run is used to evaluate the effectiveness of the EF methods, although the EF technique is also usecl to quantify forecast uncertainty in some studies. In the case of Yancy, the ensemble mean forecasts of each of the three methodologies are better than that of the control, with LAF being the best. The mean track of the LAF is close to the best track, and it predicts landfall over Taiwan. The improvements in LAF and the full BGM where both the environment and vortex are perturbed suggest the importance of combining the perturbation of the vortex and environment when the interaction between the two is appreciable. In the binary interaction case of Ed and Flo, the forecasts of Ed appear to be insensitive to perturbations of the environment and/or the vortex, which apparently results from erroneous forecasts by the model of the interaction between the subtropical ridge and Ed, as well as from the interaction between the two typhoons, thus reducing the effectiveness of the EF technique. This conclusion is reached through sensitivity experiments on the domain of the model and by adding or eliminating certain features in the model atmosphere. Nevertheless, the forecast tracks in some of the cases are improved over that of the control. On the other hand, the EF technique has little impact on the forecasts of Flo because the control forecast is already very close to the best track. The study provides a basis for the. future development of the EF technique. The limitations of this study are also addressed. For example, the above results are based on a small sample, and the study is actually a simulation, which is different than operational forecasting. Further tests of these EF techniques are proposed.
文摘Ensemble forecasting of tropical cyclone (TC) motion was studied using a primitive equation barotropic model by perturbing initial position and structure for 1979 1993 TC. The results show that TC initial position perturbation affects its track, but the ensemble mean is close to control forecast. Experiments was also performed by perturbing TC initial parameters which were used to generate TC initial field, and more improvement can be obtained by taking ensemble mean of selective member than selecting members randomly. The skill of 60 % 70 % of all cases is improved in selective ensemble mean. When the ambient steering current is weak, more improvement can be obtained over the control forecast.
基金the National Key Basic Research Program of China(2015CB452803)the Key University Science Research Project of Jiangsu Province(14KJA170005)
文摘The interaction between tropical cyclone(TC)and the large-scale mean flows such as the inter-tropical convergence zone(ITCZ)is investigated using a three-dimensional primitive equation model.Once a TC develops in the vicinity of the ITCZ region where satisfies both barotropic and baroclinic instabilities,the southeastward energy dispersion from the TC may disturb the ITCZ and thus help its breakdown.Cumulus convection can be organized in the region of cyclonic circulation,and the interaction between convective heating and the perturbation circulation may enhance the development of the waves,leading to the generation of a new tropical cyclone to the east.While the TC moves to the high latitude,the ITCZ will reform.Though repeating of this process,a synoptic-scale wave train oriented in the northwest-southeast direction can be generated and self-maintained.The results suggest that the mutual interaction among the low-frequency background flow,wave train pattern and TCs provides a possible mechanism for the origin of the summer synoptic scale wave train pattern over the western North Pacific.
