This paper deals with the comparison of cyclone forecasts from the two versions of the operational global ensemble prediction system(EPS)at the National Centre for Medium Range Weather Forecasting(NEPS).The previous v...This paper deals with the comparison of cyclone forecasts from the two versions of the operational global ensemble prediction system(EPS)at the National Centre for Medium Range Weather Forecasting(NEPS).The previous version had a horizontal resolution of 33 km with 44 ensemble members(NEPS)whereas the updated version of this EPS has a resolution of 12 km with 11 members(NEPS-UP).The ensemble mean forecasts from both the models are compared using the direct position(DPE),along(ATE)and cross track(CTE)errors.For the verification of strike probability,Brier Score(BS),Brier Skill Score(BSS),Reliability Diagram,Relative Operating Characteristic(ROC)Curve and Root Mean Square Error(RMSE)in mean Vs Spread in members are used.For verification of intensity,RMSE in maximum wind speed from the ensemble mean forecasts are compared.Comparison of ensemble mean tracks from both models showed lower errors in NEPS-UP for all forecast lead times.The decrease in the DPE,ATE and CTE in NEPS-UP was around 38%,48%and 15%respectively.NEPS-UP showed lower BS and higher BSS values indicating a better match between observed frequencies and forecast probabilities as well as higher prediction skills.The reliability diagram showed higher accuracy for NEPS-UP as compared to NEPS.The ROC curves showed that for forecasts with higher probabilities the hit rate was high in NEPSUP.There was a greater consensus between the RMSE and Spread for NEPS-UP at all lead times.It was also seen that the RMSE in mean showed a 41%decrease from NEPS to NEPS-UP.On comparing maximum wind,it was found that for all lead times the RMSE in maximum wind speed for NEPS-UP was lower than NEPS.展开更多
Previous studies on the relationship between polar motion and water mass change have mainly concentrated on the excitation of polar motion via global terrestrial water storage changes(TWSC). In view of the uneven dist...Previous studies on the relationship between polar motion and water mass change have mainly concentrated on the excitation of polar motion via global terrestrial water storage changes(TWSC). In view of the uneven distribution of global terrestrial water storage, the relationship between regional water mass change and polar motion needs to be further explored owing to the lack of documented results. In addition, given the uncertainty in the estimation of TWSC, it is required to develop appropriate indices to describe water mass change from different perspectives. The Amazon River basin(referred to Amazon hereafter), containing the world's largest river, located at around the 90°W longitude, is selected as the study area. Water vapor flux, precipitation, runoff and TWSC are selected as the indices of water mass changes to reveal the relationship between polar motion and water mass change in this giant basin. The Mann-Kendall(M-K) method, the accumulated anomaly analysis method and the curvature method are used to identify the abrupt change points; the least squares method is used to estimate the trends,and the Fast Fourier Transform(FFT) and the Ensemble Empirical Mode Decomposition(EEMD) are used to perform a periodic analysis, for all the above indices. It is shown that, of all the indices from 1948 to 2011, water vapor flux is the most closely related index to polar motion. In detail, precipitation and water vapor flux contain beat periods of polar motion; water vapor flux,precipitation and polar motion have a common M-K test abrupt change point(occurring in ca. 1968) at the 0.05 significance level; water vapor flux has a similar accumulated anomaly curve with that of polar motion; and water vapor flux is more highly correlated with polar motion than most other indexes. It is found, just like global TWSC, the χ2 component of the excitation via water vapor flux and water storage change in the Amazon follows that of observed polar motion; χ1 does not follow. However, the pattern in the Amazon that the χ2 component of the excitation by water follows that of observed polar motion is at a more significant level than in global. Finally, the new index termed Location of Vapor-based Inter Tropical Convergence Zone(LVITCZ) we proposed to describe the annual mean latitudinal location of water mass change shows a more close and visual relationship between water mass change and polar motion than other chosen indices do.展开更多
文摘This paper deals with the comparison of cyclone forecasts from the two versions of the operational global ensemble prediction system(EPS)at the National Centre for Medium Range Weather Forecasting(NEPS).The previous version had a horizontal resolution of 33 km with 44 ensemble members(NEPS)whereas the updated version of this EPS has a resolution of 12 km with 11 members(NEPS-UP).The ensemble mean forecasts from both the models are compared using the direct position(DPE),along(ATE)and cross track(CTE)errors.For the verification of strike probability,Brier Score(BS),Brier Skill Score(BSS),Reliability Diagram,Relative Operating Characteristic(ROC)Curve and Root Mean Square Error(RMSE)in mean Vs Spread in members are used.For verification of intensity,RMSE in maximum wind speed from the ensemble mean forecasts are compared.Comparison of ensemble mean tracks from both models showed lower errors in NEPS-UP for all forecast lead times.The decrease in the DPE,ATE and CTE in NEPS-UP was around 38%,48%and 15%respectively.NEPS-UP showed lower BS and higher BSS values indicating a better match between observed frequencies and forecast probabilities as well as higher prediction skills.The reliability diagram showed higher accuracy for NEPS-UP as compared to NEPS.The ROC curves showed that for forecasts with higher probabilities the hit rate was high in NEPSUP.There was a greater consensus between the RMSE and Spread for NEPS-UP at all lead times.It was also seen that the RMSE in mean showed a 41%decrease from NEPS to NEPS-UP.On comparing maximum wind,it was found that for all lead times the RMSE in maximum wind speed for NEPS-UP was lower than NEPS.
基金supported by the National Program on Key Basic Research Project (Grant No. 2012CB957802)National Key Research and Development Program of China project (Grant No. 2017YFA0603702)
文摘Previous studies on the relationship between polar motion and water mass change have mainly concentrated on the excitation of polar motion via global terrestrial water storage changes(TWSC). In view of the uneven distribution of global terrestrial water storage, the relationship between regional water mass change and polar motion needs to be further explored owing to the lack of documented results. In addition, given the uncertainty in the estimation of TWSC, it is required to develop appropriate indices to describe water mass change from different perspectives. The Amazon River basin(referred to Amazon hereafter), containing the world's largest river, located at around the 90°W longitude, is selected as the study area. Water vapor flux, precipitation, runoff and TWSC are selected as the indices of water mass changes to reveal the relationship between polar motion and water mass change in this giant basin. The Mann-Kendall(M-K) method, the accumulated anomaly analysis method and the curvature method are used to identify the abrupt change points; the least squares method is used to estimate the trends,and the Fast Fourier Transform(FFT) and the Ensemble Empirical Mode Decomposition(EEMD) are used to perform a periodic analysis, for all the above indices. It is shown that, of all the indices from 1948 to 2011, water vapor flux is the most closely related index to polar motion. In detail, precipitation and water vapor flux contain beat periods of polar motion; water vapor flux,precipitation and polar motion have a common M-K test abrupt change point(occurring in ca. 1968) at the 0.05 significance level; water vapor flux has a similar accumulated anomaly curve with that of polar motion; and water vapor flux is more highly correlated with polar motion than most other indexes. It is found, just like global TWSC, the χ2 component of the excitation via water vapor flux and water storage change in the Amazon follows that of observed polar motion; χ1 does not follow. However, the pattern in the Amazon that the χ2 component of the excitation by water follows that of observed polar motion is at a more significant level than in global. Finally, the new index termed Location of Vapor-based Inter Tropical Convergence Zone(LVITCZ) we proposed to describe the annual mean latitudinal location of water mass change shows a more close and visual relationship between water mass change and polar motion than other chosen indices do.
