ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 43,Issue 10,2017 Table of Contents
2017, 43(10):1165-1175.
DOI: 10.7519/j.issn.1000-0526.2017.10.001
Abstract:
An analysis of the climatic characteristics, circulation situation, impact system and mesoscale convective environmental conditions in 23 extreme rainstorm events in Sichuan Basin during 1981-2015 is performed by using conventional data and NCEP/NCAR reanalysis data. It is found that: (1) most extreme rainstorm events occur in continuous rainstorm processes, and rainstorms start ahead of the extreme storms, with rainstorm centers mainly in the northwest and southwest of Sichuan Basin. (2) The extreme rainstorm events occur mainly under the 500 hPa circulation background of “easthigh pressure and westlowpressure” and “shear between two highpressure”. Subtropical high would stretch toward northwest in 24 h during the rainstorm process in the “easthighpressure and westlowpressure” pattern. But subtropical high acts irregularly during the rainstorm process in the type of the “shear between two highpressure”. (3) Three extreme rainstorm events occur with landing typhoon, and the strong water vapor transportation formed by the outer circulation of typhoon has a direct impact on the heavy rain. Six extreme rainstorm events occur because of the blocking effect of the longdistance sea typhoon moving to west or north, and it is conducive to the maintenance of the heavy rain. (4) The main trigger system of the “easthighpressure and westlowpressure” is the southwest vortex and the plateau vortex while the main trigger system of the “shear between two highpressure” is the shear line, and the 700 hPa level has cold advection invasion. Two types of rainstorms occur on the divergence zone of the northeastern part of South Asia high pressure at 200 hPa, and the rainstorm center is located in the lowlevel high specific humidity area and convergence center. The stronger southerly airflow in the type of “easthigh pressure and westlowpressure” makes the rainstorm center located in the northwest of the basin, and the weaker southerly airflow in the type of “shear between two highpressure” causes the rainstorm center to stay in the southwest of the basin. (5) The characteristics of high specific humidity in the low level, high relative humidity in the whole layer, thick warm clouds, long and narrow CAPE, small vertical wind shear, high efficiency precipitation, and positive anomalies of 850 hPa humidity and pseudoequivalent temperature appear during the extreme rainstorm processes. And the 850 hPa pseudoequivalent potential temperature significantly decreases after the rainstorm. Based on the above, the conceptual model of extreme rainstorm in Sichuan Basin has been built, and it would benefit the operation of prediction.
An analysis of the climatic characteristics, circulation situation, impact system and mesoscale convective environmental conditions in 23 extreme rainstorm events in Sichuan Basin during 1981-2015 is performed by using conventional data and NCEP/NCAR reanalysis data. It is found that: (1) most extreme rainstorm events occur in continuous rainstorm processes, and rainstorms start ahead of the extreme storms, with rainstorm centers mainly in the northwest and southwest of Sichuan Basin. (2) The extreme rainstorm events occur mainly under the 500 hPa circulation background of “easthigh pressure and westlowpressure” and “shear between two highpressure”. Subtropical high would stretch toward northwest in 24 h during the rainstorm process in the “easthighpressure and westlowpressure” pattern. But subtropical high acts irregularly during the rainstorm process in the type of the “shear between two highpressure”. (3) Three extreme rainstorm events occur with landing typhoon, and the strong water vapor transportation formed by the outer circulation of typhoon has a direct impact on the heavy rain. Six extreme rainstorm events occur because of the blocking effect of the longdistance sea typhoon moving to west or north, and it is conducive to the maintenance of the heavy rain. (4) The main trigger system of the “easthighpressure and westlowpressure” is the southwest vortex and the plateau vortex while the main trigger system of the “shear between two highpressure” is the shear line, and the 700 hPa level has cold advection invasion. Two types of rainstorms occur on the divergence zone of the northeastern part of South Asia high pressure at 200 hPa, and the rainstorm center is located in the lowlevel high specific humidity area and convergence center. The stronger southerly airflow in the type of “easthigh pressure and westlowpressure” makes the rainstorm center located in the northwest of the basin, and the weaker southerly airflow in the type of “shear between two highpressure” causes the rainstorm center to stay in the southwest of the basin. (5) The characteristics of high specific humidity in the low level, high relative humidity in the whole layer, thick warm clouds, long and narrow CAPE, small vertical wind shear, high efficiency precipitation, and positive anomalies of 850 hPa humidity and pseudoequivalent temperature appear during the extreme rainstorm processes. And the 850 hPa pseudoequivalent potential temperature significantly decreases after the rainstorm. Based on the above, the conceptual model of extreme rainstorm in Sichuan Basin has been built, and it would benefit the operation of prediction.
2017, 43(10):1176-1185.
DOI: 10.7519/j.issn.1000-0526.2017.10.002
Abstract:
Based on European Center for MediumRange Weather Forecasts (ECMWF) reanalysis datasets and extreme forecast index (EFI) of ensemble prediction system, this paper analyzes the anomalous atmospheric circulation and verifies the EFI’s forecasts for extreme cold event that happened from 21 to 25 January 2016. It is found that an anomalous strong highpressure ridge maintained in central Asia and the standardized anomaly of highpressure ridge was more than 3 standard deviations and the cold vortex nearby Lake Baikal was continuously developed and enhanced. As the revising of the transverse trough, the cold vortex moved southward abnormally and extreme cold wave broke out in the East China. The verification shows the EFI can predict minimum temperature signal 7 days in advance. With the lead time extension of EFI forecast, the corresponding maximum TS score decreases, and there are different EFI thresholds for different lead time forecasts. Researches also show that the critical threshold of minimum temperature EFI for 5% percentile of the low temperature events (1-3 days) is -0.6 and for 4-7 days the critical threshold of minimum temperature EFI is -0.5. Besides, the critical threshold of minimum temperature EFI for 1% percentile of the low temperature events is -0.7. Moreover, the different lead time performance of minimum temperature EFI for 5% percentile of the low temperature events in Jiangnan, Huanghuai, Jianghuai and Jianghan Regions is the best, followed by the performance for the events in Huabei, Huanan, Southwest and Northwest, and the performance in Northeast is poor relatively.
Based on European Center for MediumRange Weather Forecasts (ECMWF) reanalysis datasets and extreme forecast index (EFI) of ensemble prediction system, this paper analyzes the anomalous atmospheric circulation and verifies the EFI’s forecasts for extreme cold event that happened from 21 to 25 January 2016. It is found that an anomalous strong highpressure ridge maintained in central Asia and the standardized anomaly of highpressure ridge was more than 3 standard deviations and the cold vortex nearby Lake Baikal was continuously developed and enhanced. As the revising of the transverse trough, the cold vortex moved southward abnormally and extreme cold wave broke out in the East China. The verification shows the EFI can predict minimum temperature signal 7 days in advance. With the lead time extension of EFI forecast, the corresponding maximum TS score decreases, and there are different EFI thresholds for different lead time forecasts. Researches also show that the critical threshold of minimum temperature EFI for 5% percentile of the low temperature events (1-3 days) is -0.6 and for 4-7 days the critical threshold of minimum temperature EFI is -0.5. Besides, the critical threshold of minimum temperature EFI for 1% percentile of the low temperature events is -0.7. Moreover, the different lead time performance of minimum temperature EFI for 5% percentile of the low temperature events in Jiangnan, Huanghuai, Jianghuai and Jianghan Regions is the best, followed by the performance for the events in Huabei, Huanan, Southwest and Northwest, and the performance in Northeast is poor relatively.
2017, 43(10):1186-1197.
DOI: 10.7519/j.issn.1000-0526.2017.10.003
Abstract:
The characteristics and its possible mechanisms of winter flooding in Hunan in 2015 were investigated. The results show that: (1) The monthly mean precipitation in Hunan was 1.6 times more than the annual mean, which was recorded as the most for the corresponding period since 1961. Meanwhile, the precipitation amount was more than 250 mm in parts of southeastern Hunan, where flooding occurred. (2) Because the precipitation amount in November was above the normal precipitation, the atmospheric circulation anomaly was the most direct cause for the winter flooding in Hunan. The unusually positive precipitation anomalies in November was produced from the stronger location of Western Pacific Subtropical High (WPSH) and the larger western extension of its ridge, which easily transported water vapor from India and Pacific to East Asia and met the cold air down to southern China. (3) When the Pacific Decadal Oscillation (PDO) was in positive phase, the El Ni〖AKn~D〗o event was important external forcing condition for abnormal precipitation. The sea surface temperature of the central and eastern equatorial Pacific and Indian Ocean were anomalously above average, leading to the enhanced anomalous ascending motion over these oceans, while the anomalous descending motion over the Maritime Continent and its surrounding area occurred. These were favorable for the westward stretch of the WPSH, the anomalous descending motion over the low latitude East Asia, and the anomalous ascending motion over the midlatitude regions. The abnormal Hadley circulation caused strong convergence over the midlatitude, which led to continuous rain weather in these areas.
The characteristics and its possible mechanisms of winter flooding in Hunan in 2015 were investigated. The results show that: (1) The monthly mean precipitation in Hunan was 1.6 times more than the annual mean, which was recorded as the most for the corresponding period since 1961. Meanwhile, the precipitation amount was more than 250 mm in parts of southeastern Hunan, where flooding occurred. (2) Because the precipitation amount in November was above the normal precipitation, the atmospheric circulation anomaly was the most direct cause for the winter flooding in Hunan. The unusually positive precipitation anomalies in November was produced from the stronger location of Western Pacific Subtropical High (WPSH) and the larger western extension of its ridge, which easily transported water vapor from India and Pacific to East Asia and met the cold air down to southern China. (3) When the Pacific Decadal Oscillation (PDO) was in positive phase, the El Ni〖AKn~D〗o event was important external forcing condition for abnormal precipitation. The sea surface temperature of the central and eastern equatorial Pacific and Indian Ocean were anomalously above average, leading to the enhanced anomalous ascending motion over these oceans, while the anomalous descending motion over the Maritime Continent and its surrounding area occurred. These were favorable for the westward stretch of the WPSH, the anomalous descending motion over the low latitude East Asia, and the anomalous ascending motion over the midlatitude regions. The abnormal Hadley circulation caused strong convergence over the midlatitude, which led to continuous rain weather in these areas.
2017, 43(10):1198-1212.
DOI: 10.7519/j.issn.1000-0526.2017.10.004
Abstract:
In this paper, an algorithm for improving the radarbased quantitative precipitation estimation (QPE) for orographic typhoon precipitation through vertical profiles of reflectivity (VPR) correction is developed. With this method the optimal ground reflectivity and the optimal ZR relationship are obtained simultaneously by the iterative solution of the objective function (the global and regional optimal fitting of VPR). The vertical rainfall structure characteristics and the increase of rainfall in the complex terrain region are fully considered and well corrected. Three typical typhoon cases are selected to verify the accuracy of this newly established method. The results show that the algorithm can display nonuniform VPR characteristics of the different regions of the ocean, plain and complex terrain region, being consistent with the observed structure of the lowlayer precipitation clouds. Compared with other ZR estimation algorithms, this improved scheme could better improve QPE in the complex terrain region. The correlation coefficient between the rainfall estimated by the new algorithm and the rain gauge observations is as high as 0.85-0.94 and the estimation error is reduced by 50% or so.
In this paper, an algorithm for improving the radarbased quantitative precipitation estimation (QPE) for orographic typhoon precipitation through vertical profiles of reflectivity (VPR) correction is developed. With this method the optimal ground reflectivity and the optimal ZR relationship are obtained simultaneously by the iterative solution of the objective function (the global and regional optimal fitting of VPR). The vertical rainfall structure characteristics and the increase of rainfall in the complex terrain region are fully considered and well corrected. Three typical typhoon cases are selected to verify the accuracy of this newly established method. The results show that the algorithm can display nonuniform VPR characteristics of the different regions of the ocean, plain and complex terrain region, being consistent with the observed structure of the lowlayer precipitation clouds. Compared with other ZR estimation algorithms, this improved scheme could better improve QPE in the complex terrain region. The correlation coefficient between the rainfall estimated by the new algorithm and the rain gauge observations is as high as 0.85-0.94 and the estimation error is reduced by 50% or so.
2017, 43(10):1213-1223.
DOI: 10.7519/j.issn.1000-0526.2017.10.005
Abstract:
Upperlevel wind data can be derived from windprofiling radar (WPR) network and Doppler radar network. In order to apply upperlevel wind data comprehensively to make full use of radar network in the field of weather analysis and numerical forecast, comparison and integration analysis of wind profiles for WPR and weather radar are conducted. After evaluating the utility and feasibility of WPR data and VAD wind profiles (VWP) by comparing with vertical profiles of horizontal winds provided from rawinsonde located in the southern suburbs of Beijing in July 2015, this paper analyzes differences of temporal and spatial representation of the two upperlevel wind data. Furthermore, different periods of WPR data are compared with VWP data to decide the optimal time resolution for integration analysis of the two kinds of wind data. Then, integration analysis is conducted by merging wind component measurements for WPR network and Doppler radar network of Guangdong Province in May 2014. The results indicate that WPR and rawinsonde data are in good agreement with root mean square error (RMSE) 2.3 m·s-1, and VWP data concides with RMSE 2.5 m·s-1. RMSE of 60 min averaged WPR data and VWP data is the lowest by comparing with that of 30 min averaged data and 6 min averaged data, and the optimal time scale for integration analysis is 60 min. Objective integration analysis field of wind data derived from WPR network and Doppler radar network can enrich the mesoscale wind field information, especially at low level.
Upperlevel wind data can be derived from windprofiling radar (WPR) network and Doppler radar network. In order to apply upperlevel wind data comprehensively to make full use of radar network in the field of weather analysis and numerical forecast, comparison and integration analysis of wind profiles for WPR and weather radar are conducted. After evaluating the utility and feasibility of WPR data and VAD wind profiles (VWP) by comparing with vertical profiles of horizontal winds provided from rawinsonde located in the southern suburbs of Beijing in July 2015, this paper analyzes differences of temporal and spatial representation of the two upperlevel wind data. Furthermore, different periods of WPR data are compared with VWP data to decide the optimal time resolution for integration analysis of the two kinds of wind data. Then, integration analysis is conducted by merging wind component measurements for WPR network and Doppler radar network of Guangdong Province in May 2014. The results indicate that WPR and rawinsonde data are in good agreement with root mean square error (RMSE) 2.3 m·s-1, and VWP data concides with RMSE 2.5 m·s-1. RMSE of 60 min averaged WPR data and VWP data is the lowest by comparing with that of 30 min averaged data and 6 min averaged data, and the optimal time scale for integration analysis is 60 min. Objective integration analysis field of wind data derived from WPR network and Doppler radar network can enrich the mesoscale wind field information, especially at low level.
2017, 43(10):1224-1231.
DOI: 10.7519/j.issn.1000-0526.2017.10.006
Abstract:
Observation of cloud base height (CBH) is crucial in modeling earthatmosphere radiation budget and for the aviation safety. CBH is estimated by combining measurements from CloudSat/CALIPSO and MODIS based on the International Satellite Cloud Climatology Project (ISCCP) cloudtype classification and a weighted distance algorithm. The proposed method is validated by ATrain data. The result indicates that the mean error of CBH is always less than 3 km, while the average error of CBH of low clouds is smaller than 1 km. The difference between the real and estimated CBHs is mainly within 1 km when distance ranges from 0 km to 500 km, and the root mean square error is smaller than 3 km. Application to the 3D cloud structure of a frontal cloud is also demonstrated.
Observation of cloud base height (CBH) is crucial in modeling earthatmosphere radiation budget and for the aviation safety. CBH is estimated by combining measurements from CloudSat/CALIPSO and MODIS based on the International Satellite Cloud Climatology Project (ISCCP) cloudtype classification and a weighted distance algorithm. The proposed method is validated by ATrain data. The result indicates that the mean error of CBH is always less than 3 km, while the average error of CBH of low clouds is smaller than 1 km. The difference between the real and estimated CBHs is mainly within 1 km when distance ranges from 0 km to 500 km, and the root mean square error is smaller than 3 km. Application to the 3D cloud structure of a frontal cloud is also demonstrated.
2017, 43(10):1232-1240.
DOI: 10.7519/j.issn.1000-0526.2017.10.007
Abstract:
A thunderstorm explanation forecast algorithm based on convective cloud characteristic temperature is proposed in order to satisfy aviation needs for efficient, high spatial and high temporal resolution shortterm thunderstorm forecasts. The algorithm is based on convective cloud top and base temperatures, -20℃ and -10℃ isothermal layer geopotential heights. Forecast performance of the algorithm, which is evaluated using the 2012-2014 observations at 35 airports in China and Global Forecast System (GFS) history products, shows high threat scores, positive skill scores and ±1.5 h forecast time accuracy in all airports. Meanwhile, the algorithm is compared with forecast performance of Terminal Aerodrome Forecast (TAF) issued in 2014 by five airport weather services in China. The results show threat scores of the algorithm are a little lower than TAF, and probability of detection equal to or much higher than TAF in the condition issued at least 8 h earlier than TAF. Thunderstorm forecast products based on the algorithm can meet the needs of aviation users.
A thunderstorm explanation forecast algorithm based on convective cloud characteristic temperature is proposed in order to satisfy aviation needs for efficient, high spatial and high temporal resolution shortterm thunderstorm forecasts. The algorithm is based on convective cloud top and base temperatures, -20℃ and -10℃ isothermal layer geopotential heights. Forecast performance of the algorithm, which is evaluated using the 2012-2014 observations at 35 airports in China and Global Forecast System (GFS) history products, shows high threat scores, positive skill scores and ±1.5 h forecast time accuracy in all airports. Meanwhile, the algorithm is compared with forecast performance of Terminal Aerodrome Forecast (TAF) issued in 2014 by five airport weather services in China. The results show threat scores of the algorithm are a little lower than TAF, and probability of detection equal to or much higher than TAF in the condition issued at least 8 h earlier than TAF. Thunderstorm forecast products based on the algorithm can meet the needs of aviation users.
2017, 43(10):1241-1248.
DOI: 10.7519/j.issn.1000-0526.2017.10.008
Abstract:
In this paper we made a statistical analysis of the road surface temperature based on observations of the selected five road stations (A1027, A1325, A1412, A1414, A1512) and the meteorological elements output from the Beijing Rapid Update Cycle (BJRUC) numerical forecasting model with 3 km resolution from 1 November 2012 to 30 March 2013. We used the stepwise regression model methods to build three types of statistical models for hourly road surface temperature in 24 h in the winter half year for the different initial forecasting times (08:00,14:00, 05:00 BT) and the different months. Then the best type is used to forecast the road surface temperature from 1 November 2013 to 30 March 2014. The results are as follows. The road surface temperature is significantly correlated to T2 and the shortwave radiation, but secondarily correlated to the longwave radiation and humidity output from RUC. Compared to the type of statistical model with the only one factor for the previous day, the type of regression model with meteorological elements of remarkable correlation inserted performs better in terms of the road surface temperature forecast accuracy by more than 25%, and the prediction error decreases by 1℃. For further enhancing the forecast accuracy rate, we selected the different initial times for verification so as to control error within ±3℃. The result of evaluation shows that the forecast value of the road surface temperature in the daytime is better than that over night, and sunny days are better than any other kinds of weather.
In this paper we made a statistical analysis of the road surface temperature based on observations of the selected five road stations (A1027, A1325, A1412, A1414, A1512) and the meteorological elements output from the Beijing Rapid Update Cycle (BJRUC) numerical forecasting model with 3 km resolution from 1 November 2012 to 30 March 2013. We used the stepwise regression model methods to build three types of statistical models for hourly road surface temperature in 24 h in the winter half year for the different initial forecasting times (08:00,14:00, 05:00 BT) and the different months. Then the best type is used to forecast the road surface temperature from 1 November 2013 to 30 March 2014. The results are as follows. The road surface temperature is significantly correlated to T2 and the shortwave radiation, but secondarily correlated to the longwave radiation and humidity output from RUC. Compared to the type of statistical model with the only one factor for the previous day, the type of regression model with meteorological elements of remarkable correlation inserted performs better in terms of the road surface temperature forecast accuracy by more than 25%, and the prediction error decreases by 1℃. For further enhancing the forecast accuracy rate, we selected the different initial times for verification so as to control error within ±3℃. The result of evaluation shows that the forecast value of the road surface temperature in the daytime is better than that over night, and sunny days are better than any other kinds of weather.
2017, 43(10):1249-1258.
DOI: 10.7519/j.issn.1000-0526.2017.10.009
Abstract:
There are three main characteristics of the 2015/2016 winter climate. (1) Temperatures were near normal over most parts of China. However, the temperature fluctuated greatly in the season, and extreme temperature events occurred frequently. (2) The areamean precipitation was above normal in China, which ranked the first since 1951. There were two main rainfall belts over southern China and northern China, respectively. (3) The East Asian winter monsoon varied greatly within the season, which was weak in the earlier stage but strong in the later period. Considering the influence of interdecadal warming background, super El Ni〖AKn~D〗o event and less Arctic sea ice in autumn, as well as prediction results of numerical models, we predicted the winter temperature of 2015/2016 was above normal in most China, which was similar to the actual situation. The prediction of more precipitation in Northeast China, northern part of North China, northeastern Xinjiang and south of the Yangtze River Valley, as well as the prediction of less precipitation in central China were correct. Predicton of the main meteorological disasters and derivative disasters was also consistent with the actual situation. However, the prediction of areas with lower temperature was smaller. We failed to predict the belownormal temperature in midwestern Inner Mongolia, northeastern part of Northwest China, southeastern part of Southwest China, and southern part of South China, especially in January 2016. Although under the same background of strong El Ni〖AKn~D〗o, the climate anomaly in the 2015/2016 winter was different from those of the 1982/1983 and 1997/1998 winters. We have analyzed the uncertainty of the influence of El Ni〖AKn~D〗o event. The predictive and analytical capabilities of winter monsoon, interseasonal variation of the Arctic oscillation, and the impact of Arctic sea ice on the winter circulation still need to be further strengthened.
There are three main characteristics of the 2015/2016 winter climate. (1) Temperatures were near normal over most parts of China. However, the temperature fluctuated greatly in the season, and extreme temperature events occurred frequently. (2) The areamean precipitation was above normal in China, which ranked the first since 1951. There were two main rainfall belts over southern China and northern China, respectively. (3) The East Asian winter monsoon varied greatly within the season, which was weak in the earlier stage but strong in the later period. Considering the influence of interdecadal warming background, super El Ni〖AKn~D〗o event and less Arctic sea ice in autumn, as well as prediction results of numerical models, we predicted the winter temperature of 2015/2016 was above normal in most China, which was similar to the actual situation. The prediction of more precipitation in Northeast China, northern part of North China, northeastern Xinjiang and south of the Yangtze River Valley, as well as the prediction of less precipitation in central China were correct. Predicton of the main meteorological disasters and derivative disasters was also consistent with the actual situation. However, the prediction of areas with lower temperature was smaller. We failed to predict the belownormal temperature in midwestern Inner Mongolia, northeastern part of Northwest China, southeastern part of Southwest China, and southern part of South China, especially in January 2016. Although under the same background of strong El Ni〖AKn~D〗o, the climate anomaly in the 2015/2016 winter was different from those of the 1982/1983 and 1997/1998 winters. We have analyzed the uncertainty of the influence of El Ni〖AKn~D〗o event. The predictive and analytical capabilities of winter monsoon, interseasonal variation of the Arctic oscillation, and the impact of Arctic sea ice on the winter circulation still need to be further strengthened.
2017, 43(10):1259-1266.
DOI: 10.7519/j.issn.1000-0526.2017.10.010
Abstract:
Influence of the early SST anomaly on the summer precipitation distribution in Shandong was discussed and possible precursor for prediction was concluded, and verified by actual condition of 2016. It is easy to cause the first EOF mode when ENSO is in the stage of development before summer, and the second mode when ENSO is in the state of decay. The summer precipitation is highly correlated with the Pacific decadal oscillation and Indian Ocean basinwide warming phase in the southeast and the peninsula of Shandong Province. Meanwhile, high impact area of Southern Indian Ocean dipole and tropical Indian Ocean dipole phase is located in the northwest of Shandong Province. These SST anomalies have certain indicative significance to the summer precipitation prediction in Shandong.
Influence of the early SST anomaly on the summer precipitation distribution in Shandong was discussed and possible precursor for prediction was concluded, and verified by actual condition of 2016. It is easy to cause the first EOF mode when ENSO is in the stage of development before summer, and the second mode when ENSO is in the state of decay. The summer precipitation is highly correlated with the Pacific decadal oscillation and Indian Ocean basinwide warming phase in the southeast and the peninsula of Shandong Province. Meanwhile, high impact area of Southern Indian Ocean dipole and tropical Indian Ocean dipole phase is located in the northwest of Shandong Province. These SST anomalies have certain indicative significance to the summer precipitation prediction in Shandong.
2017, 43(10):1267-1277.
DOI: 10.7519/j.issn.1000-0526.2017.10.011
Abstract:
Based on hindcast data of the National Climate Centre second generation monthly Dynamic Extended Range Forecast operational system (DERF2.0) from 1983 to 2015, prediction performance of the system for western Pacific subtropical high (WPSH) is evaluated by using time correlation coefficient, standardized root mean square error, anomaly sign consistency rate and Taylor diagrams. The results show that the model can predict spatial distribution of 588 dagpm contour lines and zonal wind shear position, but system bias is large and strong. The prediction performance for interannual variability of the 500 hPa height field is better than for zonal wind field. Climatological annual cycle information of WPSH are well represented, but there are obvious systematic deviations. The prediction is larger for WPSH area, stronger for intensity, by north for ridge line, and by west for west ridge point than the observation. The prediction performance for interannual variability of WPSH is good. The best is for intensity, secondly for area, and the poorest for ridge line. The prediction performance depends on the lead time. With time approaching, the prediction performance shows an increasing trend. Updating forecast is needed in time for rolling correction in operation. The performance of model WPSH prediction for area ahead of 0-20 days, for intensity ahead of 0-2 days, for western ridge point ahead of 0-5 days, for ridge line ahead of 0-7 days is better than persistence forecast. This can be used as a reference in forecasting operation.
Based on hindcast data of the National Climate Centre second generation monthly Dynamic Extended Range Forecast operational system (DERF2.0) from 1983 to 2015, prediction performance of the system for western Pacific subtropical high (WPSH) is evaluated by using time correlation coefficient, standardized root mean square error, anomaly sign consistency rate and Taylor diagrams. The results show that the model can predict spatial distribution of 588 dagpm contour lines and zonal wind shear position, but system bias is large and strong. The prediction performance for interannual variability of the 500 hPa height field is better than for zonal wind field. Climatological annual cycle information of WPSH are well represented, but there are obvious systematic deviations. The prediction is larger for WPSH area, stronger for intensity, by north for ridge line, and by west for west ridge point than the observation. The prediction performance for interannual variability of WPSH is good. The best is for intensity, secondly for area, and the poorest for ridge line. The prediction performance depends on the lead time. With time approaching, the prediction performance shows an increasing trend. Updating forecast is needed in time for rolling correction in operation. The performance of model WPSH prediction for area ahead of 0-20 days, for intensity ahead of 0-2 days, for western ridge point ahead of 0-5 days, for ridge line ahead of 0-7 days is better than persistence forecast. This can be used as a reference in forecasting operation.
2017, 43(10):1278-1286.
DOI: 10.7519/j.issn.1000-0526.2017.10.012
Abstract:
Since mid1990s, there has been a reduction in frequency and intensity of landfall typhoon over South China (SC). This research reveals that the typhoon variation is jointly affected by the interannual and decadal typhoons and the largescale atmospheric circulation systems. On the other hand, it may be related to the Pacific Decadal Oscillation (PDO). By using the interannual increment method to get rid of the decadal variation, during the eastern La Ni〖AKn~D〗a (the central El Ni〖AKn~D〗o) episode in the preceding winter, it would be a stronger (weaker) crossequatorial flow over 120°-130°E, followed by convergence zone and monsoon trough with the location more northward (southward). This kind of atmosphere and ocean configuration could make the accumulated cyclone energy (ACE) stronger (weaker). Therefore, the typhoon would be more powerful, which reflects the interannual interaction among the typhoon, the sea surface temperature (SST) and the atmospheric circulation systems. Finally, adopting the principal component regression technique based on the interannual incremental method, the prediction model of ACE index is constructed, whose hindcast correlation coefficient is up to 0.80 for the recent 30 years. And the 2014 and 2015 prediction results are consistent with the observations.
Since mid1990s, there has been a reduction in frequency and intensity of landfall typhoon over South China (SC). This research reveals that the typhoon variation is jointly affected by the interannual and decadal typhoons and the largescale atmospheric circulation systems. On the other hand, it may be related to the Pacific Decadal Oscillation (PDO). By using the interannual increment method to get rid of the decadal variation, during the eastern La Ni〖AKn~D〗a (the central El Ni〖AKn~D〗o) episode in the preceding winter, it would be a stronger (weaker) crossequatorial flow over 120°-130°E, followed by convergence zone and monsoon trough with the location more northward (southward). This kind of atmosphere and ocean configuration could make the accumulated cyclone energy (ACE) stronger (weaker). Therefore, the typhoon would be more powerful, which reflects the interannual interaction among the typhoon, the sea surface temperature (SST) and the atmospheric circulation systems. Finally, adopting the principal component regression technique based on the interannual incremental method, the prediction model of ACE index is constructed, whose hindcast correlation coefficient is up to 0.80 for the recent 30 years. And the 2014 and 2015 prediction results are consistent with the observations.
2017, 43(10):1287-1295.
DOI: 10.7519/j.issn.1000-0526.2017.10.013
Abstract:
In 2016, there were three landing and four impacting typhoons seen in Fujian Province, showing the nonuniform temporal distribution and serious disasters. Analysis indicates that main causation of Fujian typhoon distribution in 2016 is due to the evolution of SSTA (sea surface temperature anomaly) over the central and eastern equatorial Pacific and the response of atmospheric circulation. The enhancing or stronger monsoon trough favors the typhoon groupgenesis from late July to midAugust over northwestern Pacific and the active influence of Typhoons “Meranti” and “Malakas” within a weak in midSeptember, characterized by significant lowfrequency variability. Statistical analysis also demonstrates that the number of typhoon genesis and impacting Fujian may be strongly linked to the tropical intraseasonal oscillation. Nearly 70% typhoons are generated when MJO is active during phases 5-7. Prediction assessment suggests that the extendedrangeforecast based on the atmospheric lowfrequency theory could fill the gap between monthlyseasonalterm prediction and shortmediumterm weather forecast.
In 2016, there were three landing and four impacting typhoons seen in Fujian Province, showing the nonuniform temporal distribution and serious disasters. Analysis indicates that main causation of Fujian typhoon distribution in 2016 is due to the evolution of SSTA (sea surface temperature anomaly) over the central and eastern equatorial Pacific and the response of atmospheric circulation. The enhancing or stronger monsoon trough favors the typhoon groupgenesis from late July to midAugust over northwestern Pacific and the active influence of Typhoons “Meranti” and “Malakas” within a weak in midSeptember, characterized by significant lowfrequency variability. Statistical analysis also demonstrates that the number of typhoon genesis and impacting Fujian may be strongly linked to the tropical intraseasonal oscillation. Nearly 70% typhoons are generated when MJO is active during phases 5-7. Prediction assessment suggests that the extendedrangeforecast based on the atmospheric lowfrequency theory could fill the gap between monthlyseasonalterm prediction and shortmediumterm weather forecast.
2017, 43(10):1296-1301.
DOI: 10.7519/j.issn.1000-0526.2017.10.014
Abstract:
During the spring 2017, precipitation averaged over China is 139.1 mm, close to normal. The spatial distribution presents the “more in west and less in east” anomalous pattern. The spring temperature is close to or above normal over the most part of China, with average temperature is 11.1℃, 0.7℃ above normal. The Pacific decadal oscillation is at the positive phase, which provides a warm decadal background. Besides, the zonal pattern of atmospheric anomalies dominates the North Asia, the East Asia trough is more eastern than normal, and the positive geopotential height at 500 hPa controls most China, coleading to the warm condition in the preceding spring. In addition, the SST of the equatorial central and eastern Pacific is lower than normal, accompanied by warm SST anomalies at over the subtropical Pacific and West Pacific Region, which is good for less precipitation in South China and Northeast China, and more precipitation in Southwest China during the following spring. For the internal causes, Northeast China, South China, and Jiangnan Areas are dominated by the north wind and water vapor divergent anomalies, which may lead to the less precipitation in these regions. However, warm water vapor from the Bay of Bengal encounters with the north cold wind from the plateau, producing more precipitation over the Southwest China. This is another major cause for the circulation anomaly in 2017.
During the spring 2017, precipitation averaged over China is 139.1 mm, close to normal. The spatial distribution presents the “more in west and less in east” anomalous pattern. The spring temperature is close to or above normal over the most part of China, with average temperature is 11.1℃, 0.7℃ above normal. The Pacific decadal oscillation is at the positive phase, which provides a warm decadal background. Besides, the zonal pattern of atmospheric anomalies dominates the North Asia, the East Asia trough is more eastern than normal, and the positive geopotential height at 500 hPa controls most China, coleading to the warm condition in the preceding spring. In addition, the SST of the equatorial central and eastern Pacific is lower than normal, accompanied by warm SST anomalies at over the subtropical Pacific and West Pacific Region, which is good for less precipitation in South China and Northeast China, and more precipitation in Southwest China during the following spring. For the internal causes, Northeast China, South China, and Jiangnan Areas are dominated by the north wind and water vapor divergent anomalies, which may lead to the less precipitation in these regions. However, warm water vapor from the Bay of Bengal encounters with the north cold wind from the plateau, producing more precipitation over the Southwest China. This is another major cause for the circulation anomaly in 2017.
2017, 43(10):1302-1308.
DOI: 10.7519/j.issn.1000-0526.2017.10.015
Abstract:
The following are the main characteristics of the general circulation of atmosphere in July 2017. There were two polar vortex centers with stronger strength than normal in the Northern Hemisphere. The midhigh latitude circulation showed a fivewave pattern. The strength of subtropical high in the Northern Hemisphere was stronger than usual, the location of northwestern Pacific subtropical high was by north and the ridge line oscillated greatly. In July, the monthly mean temperature of China was 23.2℃, 1.3℃ higher than usual. The monthly mean precipitation of China was 112.5 mm, 6.7% less than usual, and especially in the west of Northeast China, northeast of Jiangnan, southwest of Jianghuai and north of Xinjiang; it rained much less. The heavy precipitation processes in July mainly occurred in Northeast China and Southern China, and there were nine regional torrential rain processes. What’s more, the rainstorm from 13 to 14 July broke the extreme values in historic records in many aspects. Eight typhoons were generated in the Northwest Pacific in July, of which seven were active and three landed in China. The number of typhoon is more than normal and is the maximum between with 1994, 1967 and 1971. In addition, drought hit the east of Inner Mongolia, and the regions of Jianghuai and Jianghan. Heat wave continued in central and eastern China as well as Xinjiang, lasting as long as 20 days. High temperature weather over 35℃ happened at 1884 stations and the extreme high temperature was found in Turpan, being 49℃.
The following are the main characteristics of the general circulation of atmosphere in July 2017. There were two polar vortex centers with stronger strength than normal in the Northern Hemisphere. The midhigh latitude circulation showed a fivewave pattern. The strength of subtropical high in the Northern Hemisphere was stronger than usual, the location of northwestern Pacific subtropical high was by north and the ridge line oscillated greatly. In July, the monthly mean temperature of China was 23.2℃, 1.3℃ higher than usual. The monthly mean precipitation of China was 112.5 mm, 6.7% less than usual, and especially in the west of Northeast China, northeast of Jiangnan, southwest of Jianghuai and north of Xinjiang; it rained much less. The heavy precipitation processes in July mainly occurred in Northeast China and Southern China, and there were nine regional torrential rain processes. What’s more, the rainstorm from 13 to 14 July broke the extreme values in historic records in many aspects. Eight typhoons were generated in the Northwest Pacific in July, of which seven were active and three landed in China. The number of typhoon is more than normal and is the maximum between with 1994, 1967 and 1971. In addition, drought hit the east of Inner Mongolia, and the regions of Jianghuai and Jianghan. Heat wave continued in central and eastern China as well as Xinjiang, lasting as long as 20 days. High temperature weather over 35℃ happened at 1884 stations and the extreme high temperature was found in Turpan, being 49℃.
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