ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 42,Issue 4,2016 Table of Contents
2016, 42(4):389-397.
DOI: 10.7519/j.issn.1000-0526.2016.04.001
Abstract:
According to the characteristics of severe convective weather and the requirements to focus on various factors, objectbased verification method is developed to find the potential value of forecasts. First of all, convection objects, such as convective cells and severe convective weather area, are identified in both forecasts and observations based on intensity and area which meet certain requirements. Then objects in the two datasets are matched according to the area, distance and morphology. After that, objects in forecasts are verified in five aspects, grade TS score, grade size, distance of center of gravity, crosscorrelation and morphology (axial and ellipticity). Finally, based on the evaluation preference of users, verification scores by weighted average and evaluation for area, position and shape are provided. Three types of severe convection forecasting products, such as QPF, REF, or convection probability product of the Chinese Meteorological Administration (CMA) SWAN (Severe Weather Analysis and Nowcasting) system, are verified by this objectbased method. This method can provide quantitative verification in coincidence and deviation for area, position or intensity. It also can explain why the regular verification scores (such as TS score) are low. Therefore, this method can privide more effective verification and evaluation information for forecasters, combined with above elements.
According to the characteristics of severe convective weather and the requirements to focus on various factors, objectbased verification method is developed to find the potential value of forecasts. First of all, convection objects, such as convective cells and severe convective weather area, are identified in both forecasts and observations based on intensity and area which meet certain requirements. Then objects in the two datasets are matched according to the area, distance and morphology. After that, objects in forecasts are verified in five aspects, grade TS score, grade size, distance of center of gravity, crosscorrelation and morphology (axial and ellipticity). Finally, based on the evaluation preference of users, verification scores by weighted average and evaluation for area, position and shape are provided. Three types of severe convection forecasting products, such as QPF, REF, or convection probability product of the Chinese Meteorological Administration (CMA) SWAN (Severe Weather Analysis and Nowcasting) system, are verified by this objectbased method. This method can provide quantitative verification in coincidence and deviation for area, position or intensity. It also can explain why the regular verification scores (such as TS score) are low. Therefore, this method can privide more effective verification and evaluation information for forecasters, combined with above elements.
2016, 42(4):398-405.
DOI: 10.7519/j.issn.1000-0526.2016.04.002
Abstract:
The logistic discriminant model (LDM) is used in the heavy rainfall forecasting with three different schemes. In Scheme 1, 14 impact factors are imported into the model directly so that the model has high simulation skill but low forecast skill because of the colinearity effect among the factors and noise signals. In Scheme 2, the principal component analysis is applied to all the impact factors and only the first 6 leading principal components are used in building the model. Compared to Scheme 1, the simulation skill in Scheme 2 is lower but the forecast skill is higher due to the elimination of both colinearity effect and noise signals. In Scheme 3, the Bootstrap sampling technique is applied to get subsamples in order to obtain the model parameters. Thus the fluctuations in the original time series have been disturbed and only the stable information is remained. Though both the degree of freedom in the fitting and the simulation skill in this scheme are lower than in Scheme 2, the forecast skill is the highest of all the three schemes. Based on above results and by using the forecast data of ECMWF (European Centre for MediumRange Weather Forecasts), an objective LDM heavy rainfall forecasting system has been established and used in the forecasting operation at the National Meteorological Centre of China. Verification results in 2013-2014 indicate that the TS skill using the LDM scheme is generally higher than using the numerical model outputs directly.
The logistic discriminant model (LDM) is used in the heavy rainfall forecasting with three different schemes. In Scheme 1, 14 impact factors are imported into the model directly so that the model has high simulation skill but low forecast skill because of the colinearity effect among the factors and noise signals. In Scheme 2, the principal component analysis is applied to all the impact factors and only the first 6 leading principal components are used in building the model. Compared to Scheme 1, the simulation skill in Scheme 2 is lower but the forecast skill is higher due to the elimination of both colinearity effect and noise signals. In Scheme 3, the Bootstrap sampling technique is applied to get subsamples in order to obtain the model parameters. Thus the fluctuations in the original time series have been disturbed and only the stable information is remained. Though both the degree of freedom in the fitting and the simulation skill in this scheme are lower than in Scheme 2, the forecast skill is the highest of all the three schemes. Based on above results and by using the forecast data of ECMWF (European Centre for MediumRange Weather Forecasts), an objective LDM heavy rainfall forecasting system has been established and used in the forecasting operation at the National Meteorological Centre of China. Verification results in 2013-2014 indicate that the TS skill using the LDM scheme is generally higher than using the numerical model outputs directly.
2016, 42(4):406-414.
DOI: 10.7519/j.issn.1000-0526.2016.04.003
Abstract:
By using National Centers for Environmental Prediction (NCEP) Final (FNL) operational global analysis data, the formation and developing mechanisms of the two vortices that caused snowstorms, on 16 and 25 February 2015 are investigated in terms of dynamics diagnosis. The results show that the formation and strengthening of vortices are the direct causes for the snowstorms, but the associated mechanisms are quite different in the two snowstorm cases. Positive tendencies of relative vorticity caused by convergence in lower troposphere and vertical transportation are the mainly forcing items for the formation of vortices in the two cases, respectively. On 16 February, there was a vortex moving eastward at 500 hPa. The cold advection near the bottom of the vortex deepened the trough at 500 hPa and the positive vorticity advection strengthened. Therefore, the increase of differential vorticity advection〖JP2〗 resulted in the developing of upward motion, and then the〖JP〗 enhancement of the convergence at 850 hPa. On the other hand, on 25 February, the vertical vorticity transport by strong upward movement was the major developing mechanism of the vortex at 850 hPa.
By using National Centers for Environmental Prediction (NCEP) Final (FNL) operational global analysis data, the formation and developing mechanisms of the two vortices that caused snowstorms, on 16 and 25 February 2015 are investigated in terms of dynamics diagnosis. The results show that the formation and strengthening of vortices are the direct causes for the snowstorms, but the associated mechanisms are quite different in the two snowstorm cases. Positive tendencies of relative vorticity caused by convergence in lower troposphere and vertical transportation are the mainly forcing items for the formation of vortices in the two cases, respectively. On 16 February, there was a vortex moving eastward at 500 hPa. The cold advection near the bottom of the vortex deepened the trough at 500 hPa and the positive vorticity advection strengthened. Therefore, the increase of differential vorticity advection〖JP2〗 resulted in the developing of upward motion, and then the〖JP〗 enhancement of the convergence at 850 hPa. On the other hand, on 25 February, the vertical vorticity transport by strong upward movement was the major developing mechanism of the vortex at 850 hPa.
2016, 42(4):415-423.
DOI: 10.7519/j.issn.1000-0526.2016.04.004
Abstract:
Using the multilayer wind data of the Typhoon Kalmaegi from the 90 m meteorological anemometer tower in Hainan Province, this paper analyzes the spatial and temporal characteristics, turbulence intensity, vertical wind shear and gust coefficient of the surface wind during the landing of Typhoon Kalmaegi. The results show that the nearsurface wind at different heights presents the “M” pattern during the typhoon’s landfall. The maximum wind speed appears in the rear wind circle. The wind direction rotates around by 180° before and after the typhoon sweeps the area. The nearsurface wind increases along speed with the increase of height. The vertical shear of wind speed at different heights accords with logarithmic and exponential rule. Roughness, wind profile exponent, turbulence intensity and gust coefficient have negative correlations with the wind speed. They decrease with the wind speed’s increasing. The roughness characteristic is “increasingdecreasingincreasing” with the wind speed from typhoon periphery to eye. The wind speed vertical shear is strong in the typhoon eye and weak in the wind circle. The turbulence intensity is weak in the strong wind area and strong in the weak wind area. The turbulence intensity decreases with height in the typhoon wind circle but the situation is opposite in the typhoon eye. In general, the gust coefficient increases with the hight and conforms to exponential rule in different layers. In addition, the gust coefficient decreases with the wind speed until the wind speed reaches a high level.
Using the multilayer wind data of the Typhoon Kalmaegi from the 90 m meteorological anemometer tower in Hainan Province, this paper analyzes the spatial and temporal characteristics, turbulence intensity, vertical wind shear and gust coefficient of the surface wind during the landing of Typhoon Kalmaegi. The results show that the nearsurface wind at different heights presents the “M” pattern during the typhoon’s landfall. The maximum wind speed appears in the rear wind circle. The wind direction rotates around by 180° before and after the typhoon sweeps the area. The nearsurface wind increases along speed with the increase of height. The vertical shear of wind speed at different heights accords with logarithmic and exponential rule. Roughness, wind profile exponent, turbulence intensity and gust coefficient have negative correlations with the wind speed. They decrease with the wind speed’s increasing. The roughness characteristic is “increasingdecreasingincreasing” with the wind speed from typhoon periphery to eye. The wind speed vertical shear is strong in the typhoon eye and weak in the wind circle. The turbulence intensity is weak in the strong wind area and strong in the weak wind area. The turbulence intensity decreases with height in the typhoon wind circle but the situation is opposite in the typhoon eye. In general, the gust coefficient increases with the hight and conforms to exponential rule in different layers. In addition, the gust coefficient decreases with the wind speed until the wind speed reaches a high level.
2016, 42(4):424-435.
DOI: 10.7519/j.issn.1000-0526.2016.04.005
Abstract:
Radiosonde observations and surface observations, which are obviously different in spatiotemporal resolutions, serve as the most commonly used and vital data sources in weather analysis and numerical prediction. Further studies are required on how to use the surface observation data with high spatiotemporal resolution to supplement deficiencies and shortages in radiosonde observations in some areas, especially on the effect of using mountain station data on the circulation of lowlevel troposphere and on the indicative significance to the refinement of wind field analysis of numerical weather forecast. By analyzing various methods used in data assimilation of mountain station observations, this paper investigates the contribution of the supplementary data of radiosonde observation to the data assimilation. As a test case, the surface data and radiosonde observation at 00 UTC 29 June 2013 are adopted for data assimilation, which takes the surface observations of mountain station as radiosonde data and surface data in assimilation analysis. 〖JP2〗The results indicate that when the surface observation of mountain stations is used as radiosonde data, they have positive effects on the 850 hPa and 925 hPa wind data assimilation analysis. The comparison of using the surface observation as radiosonde data and as surface data shows no apparent difference in 24 h forecasting test on the height and wind fields at 850 hPa and 700 hPa levels. However, the 24 h precipitation forecast results show a weak positive contribution to rainfall intensity and location prediction when using the surface observation of mountain stations as radiosonde data. Continuous precipitation forecast tests prove that in the southwest areas where more mountain stations are located, the precipitation forecasting scores for light rain, moderate rain and heavy rain with station observations used as radiosonde data are better than those with station observations as surface data, and their forecast bias are also smaller. But in the other areas of China, no obvious difference is found in precipitation tests by using mountain data as the radiosonde data or the surface data.
Radiosonde observations and surface observations, which are obviously different in spatiotemporal resolutions, serve as the most commonly used and vital data sources in weather analysis and numerical prediction. Further studies are required on how to use the surface observation data with high spatiotemporal resolution to supplement deficiencies and shortages in radiosonde observations in some areas, especially on the effect of using mountain station data on the circulation of lowlevel troposphere and on the indicative significance to the refinement of wind field analysis of numerical weather forecast. By analyzing various methods used in data assimilation of mountain station observations, this paper investigates the contribution of the supplementary data of radiosonde observation to the data assimilation. As a test case, the surface data and radiosonde observation at 00 UTC 29 June 2013 are adopted for data assimilation, which takes the surface observations of mountain station as radiosonde data and surface data in assimilation analysis. 〖JP2〗The results indicate that when the surface observation of mountain stations is used as radiosonde data, they have positive effects on the 850 hPa and 925 hPa wind data assimilation analysis. The comparison of using the surface observation as radiosonde data and as surface data shows no apparent difference in 24 h forecasting test on the height and wind fields at 850 hPa and 700 hPa levels. However, the 24 h precipitation forecast results show a weak positive contribution to rainfall intensity and location prediction when using the surface observation of mountain stations as radiosonde data. Continuous precipitation forecast tests prove that in the southwest areas where more mountain stations are located, the precipitation forecasting scores for light rain, moderate rain and heavy rain with station observations used as radiosonde data are better than those with station observations as surface data, and their forecast bias are also smaller. But in the other areas of China, no obvious difference is found in precipitation tests by using mountain data as the radiosonde data or the surface data.
2016, 42(4):436-442.
DOI: 10.7519/j.issn.1000-0526.2016.04.006
Abstract:
Based on the acid rain records over 20 years in Tianjin, characteristics and longterm trend of acid rain were analyzed. The results show that the precipitation pH varies in the range of 3.30-8.80, with a large averaged seasonal variation from 1992 to 2012. Totally, there are 182 acid rain events (pH below 5.6), and the frequency is 21.2%. The annual mean precipitation pH shows different variation patterns in the periods of 1992-2002 and 2003-2012. In the former period, it is a steady slow increasing trend and the averaged annual rate of precipitation pH is 0.13 a-1, in the later period, the increasing trend slows down and the averaged annual rate of precipitation pH is 0.11 a-1. The seasonal variations of the pH values are different in recent 20 years. There is no obvious changes in spring, but significant increasing trend in summer and autumn. Precipitation pH value in summer and autumn is the most important factor that affects the pH values of longterm trend in Tianjin. The analysis of correlation indicates that the precipitation pH value is negatively correlated with concentrations of SO2 and NO2. Rainfall is acidic due to the influence of local air pollution in addition to the influence of the pollution source around Tianjin.
Based on the acid rain records over 20 years in Tianjin, characteristics and longterm trend of acid rain were analyzed. The results show that the precipitation pH varies in the range of 3.30-8.80, with a large averaged seasonal variation from 1992 to 2012. Totally, there are 182 acid rain events (pH below 5.6), and the frequency is 21.2%. The annual mean precipitation pH shows different variation patterns in the periods of 1992-2002 and 2003-2012. In the former period, it is a steady slow increasing trend and the averaged annual rate of precipitation pH is 0.13 a-1, in the later period, the increasing trend slows down and the averaged annual rate of precipitation pH is 0.11 a-1. The seasonal variations of the pH values are different in recent 20 years. There is no obvious changes in spring, but significant increasing trend in summer and autumn. Precipitation pH value in summer and autumn is the most important factor that affects the pH values of longterm trend in Tianjin. The analysis of correlation indicates that the precipitation pH value is negatively correlated with concentrations of SO2 and NO2. Rainfall is acidic due to the influence of local air pollution in addition to the influence of the pollution source around Tianjin.
2016, 42(4):443-449.
DOI: 10.7519/j.issn.1000-0526.2016.04.007
Abstract:
Based on atmospheric aerosol mass concentration and relative meteorological data in Tianjin urban areas during the Spring Festivals of 2009-2014, the distribution characteristics of aerosol concentration spectrum were gained and the impact factors of these distribution characteristics including fireworks and meteorological conditions were analyzed. The results showed that PM2.5 mass concentration reached its peak value in the New Year Eve due to firing fireworks. With the continuous fog and haze during the Spring Festival, firing fireworks made the PM2.5 concentration reach 1240 μg·m-3 in 2013 and this is the highest value in recent years. During the Spring Festival of 2014, the decreasing amount of fireworks and good condition of pollutant dispersion were the causes for lower PM2.5 mass concentration than in 2013. Distribution characteristics of aerosol number concentration spectrum had significantly differences in different weather conditions. Aerosol number concentrations during firing fireworks were comparable with that of fog and haze events.
Based on atmospheric aerosol mass concentration and relative meteorological data in Tianjin urban areas during the Spring Festivals of 2009-2014, the distribution characteristics of aerosol concentration spectrum were gained and the impact factors of these distribution characteristics including fireworks and meteorological conditions were analyzed. The results showed that PM2.5 mass concentration reached its peak value in the New Year Eve due to firing fireworks. With the continuous fog and haze during the Spring Festival, firing fireworks made the PM2.5 concentration reach 1240 μg·m-3 in 2013 and this is the highest value in recent years. During the Spring Festival of 2014, the decreasing amount of fireworks and good condition of pollutant dispersion were the causes for lower PM2.5 mass concentration than in 2013. Distribution characteristics of aerosol number concentration spectrum had significantly differences in different weather conditions. Aerosol number concentrations during firing fireworks were comparable with that of fog and haze events.
2016, 42(4):450-455.
DOI: 10.7519/j.issn.1000-0526.2016.04.008
Abstract:
In order to establish the drought weather index insurance model of summer corn, this paper analyzed the relationship between the precipitation anomaly from the male stage to the ripening stage (critical period of yield formation ) and historical yield loss based on the 1971-2010 daily precipitation data from 15 agrometeorological observation stations, proposed the standard of insurance claims of summer corn drought, and then revised the insurance rate using the result of drought risk assessment. The drought weather index insurance products of summer corn were obtained and later the insurance products were applied in Suixi County of Huaibei City, Anhui Province as an experiment. The results show that the application of weather index insurance product can basically reflect the actual drought risk of summer corn， and objectively and quickly provide the economic compensation of agricultural disaster.
In order to establish the drought weather index insurance model of summer corn, this paper analyzed the relationship between the precipitation anomaly from the male stage to the ripening stage (critical period of yield formation ) and historical yield loss based on the 1971-2010 daily precipitation data from 15 agrometeorological observation stations, proposed the standard of insurance claims of summer corn drought, and then revised the insurance rate using the result of drought risk assessment. The drought weather index insurance products of summer corn were obtained and later the insurance products were applied in Suixi County of Huaibei City, Anhui Province as an experiment. The results show that the application of weather index insurance product can basically reflect the actual drought risk of summer corn， and objectively and quickly provide the economic compensation of agricultural disaster.
2016, 42(4):456-465.
DOI: 10.7519/j.issn.1000-0526.2016.04.009
Abstract:
The accuracy of numerical models has been improved continuously and weather forecast and climate prediction rely on numerical models more and more. Numerical models are the equations which describe the motion and thermodynamic processes of the atmosphere. Statistical methods are also widely used to numerical models, becoming important components of numerical models. This paper reviews some new advances in the application of statistical method to numerical models. Firstly, application of statistical methods to data assimilation, ensemble forecast, parameterization of physical processes, statistical interpretation, extendedrange weather forecasts and model verification for numerical model are analyzed. Then, the latest application of Bayes statistics to numerical models is elaborated. Finally, several important research trends for future application of statistical methods to numerical models are put forward.
The accuracy of numerical models has been improved continuously and weather forecast and climate prediction rely on numerical models more and more. Numerical models are the equations which describe the motion and thermodynamic processes of the atmosphere. Statistical methods are also widely used to numerical models, becoming important components of numerical models. This paper reviews some new advances in the application of statistical method to numerical models. Firstly, application of statistical methods to data assimilation, ensemble forecast, parameterization of physical processes, statistical interpretation, extendedrange weather forecasts and model verification for numerical model are analyzed. Then, the latest application of Bayes statistics to numerical models is elaborated. Finally, several important research trends for future application of statistical methods to numerical models are put forward.
2016, 42(4):466-471.
DOI: 10.7519/j.issn.1000-0526.2016.04.010
Abstract:
Wind speed forecasting is the basis of wind power forecasting, and its accuracy affects the efficiency of the wind farm seriously. In order to improve the accuracy of shortterm wind speed forecasting, the WRF mesoscale numerical model was used to predict the wind speed of a wind farm in the eastern coasts of China. Besides, the Extreme Learning Machine (ELM) algorithm was used for further correction. The results show that, the WRF model has a better effect on the wind speed, wind direction and other meteorological elements. After correcting the wind speed forecasting of the WRF model, with the ELM algorithm, the error of wind speed forecasting becomes smaller, and the relative root mean square error and relative mean absolute error are reduced by 20%-30%. Thus, the ELM algorithm is qualified to have better correction capability for the wind speed of WRF model forecasting compared with other intelligent algorithms (BP neural network, SVM algorithm), and can improve the accuracy of wind speed forecasting effectively.
Wind speed forecasting is the basis of wind power forecasting, and its accuracy affects the efficiency of the wind farm seriously. In order to improve the accuracy of shortterm wind speed forecasting, the WRF mesoscale numerical model was used to predict the wind speed of a wind farm in the eastern coasts of China. Besides, the Extreme Learning Machine (ELM) algorithm was used for further correction. The results show that, the WRF model has a better effect on the wind speed, wind direction and other meteorological elements. After correcting the wind speed forecasting of the WRF model, with the ELM algorithm, the error of wind speed forecasting becomes smaller, and the relative root mean square error and relative mean absolute error are reduced by 20%-30%. Thus, the ELM algorithm is qualified to have better correction capability for the wind speed of WRF model forecasting compared with other intelligent algorithms (BP neural network, SVM algorithm), and can improve the accuracy of wind speed forecasting effectively.
LIAO Yaoming
,
WANG Ling
,
WANG Zunya
,
YE Dianxiu
,
ZHOU Bing
,
HOU Wei
,
WANG Youmin
,
ZHU Xiaojin
,
HUANG Dapeng
,
ZHAO Shanshan
,
ZHONG Hailing
,
WANG Yang
,
LI Ying
,
JIANG Yundi
,
ZENG Hongling
2016, 42(4):472-480.
DOI: 10.7519/j.issn.1000-0526.2016.04.011
Abstract:
The anomaly of annual mean surface air temperature over China in 2015 is 0.9℃, warmer than normal years making the year the warmest since 1961. The annual mean temperature in South China broke the historical record while the regions of Northeast, Northwest and North China has experienced the second warmest year since 1961. The warmer air temperature was not only found in annual mean, but also in all the four seasons. The annual mean precipitation in 2015 in China was 648.8 mm, 3% more than normal. More anomalies of precipitation were observed in most parts of the middle and lower reaches of Yangtze River, Guangxi and Xinjiang while less precipitation were seen in the western part of Southwest, Hainan and Liaoning. Seasonal precipitation is less in winter and summer, near normal in spring, but obviously above normal in autumn. There were too many torrential rain processes over the southern part of China, causing the South flooding and the North drought in summer. Urban waterlogging was very heavy in some cities, like Shanghai and Nanjing. However, North China, the eastern part of Northwest, and Liaoning suffered from serious and successive droughts through summer and autumn. In November severe precipitation appeared in South of China. Xinjiang had extremely hot wave in the mid summer, while the middle and lower reaches of Yangtze River Basin experienced cooler summer continuously for two years due to more rainfall. Landing typhoons were less but with more powerful strength. For instance, the landing Typhoon of Mujigae caused the severe disasters. There were eleven largescale and persistent haze events over China in 2015. The frequent foghaze events hit the central and eastern China from November to December, and the most serious event occurred in Huanghuai and North China from 27 November to 1 December in 2015.
The anomaly of annual mean surface air temperature over China in 2015 is 0.9℃, warmer than normal years making the year the warmest since 1961. The annual mean temperature in South China broke the historical record while the regions of Northeast, Northwest and North China has experienced the second warmest year since 1961. The warmer air temperature was not only found in annual mean, but also in all the four seasons. The annual mean precipitation in 2015 in China was 648.8 mm, 3% more than normal. More anomalies of precipitation were observed in most parts of the middle and lower reaches of Yangtze River, Guangxi and Xinjiang while less precipitation were seen in the western part of Southwest, Hainan and Liaoning. Seasonal precipitation is less in winter and summer, near normal in spring, but obviously above normal in autumn. There were too many torrential rain processes over the southern part of China, causing the South flooding and the North drought in summer. Urban waterlogging was very heavy in some cities, like Shanghai and Nanjing. However, North China, the eastern part of Northwest, and Liaoning suffered from serious and successive droughts through summer and autumn. In November severe precipitation appeared in South of China. Xinjiang had extremely hot wave in the mid summer, while the middle and lower reaches of Yangtze River Basin experienced cooler summer continuously for two years due to more rainfall. Landing typhoons were less but with more powerful strength. For instance, the landing Typhoon of Mujigae caused the severe disasters. There were eleven largescale and persistent haze events over China in 2015. The frequent foghaze events hit the central and eastern China from November to December, and the most serious event occurred in Huanghuai and North China from 27 November to 1 December in 2015.
2016, 42(4):481-488.
DOI: 10.7519/j.issn.1000-0526.2016.04.012
Abstract:
Anomalies of oceanic and atmospheric circulations are analyzed and their impacts on temperature and precipitation anomalies of 2015 in China are investigated in this paper. It is found that the East Asian Winter Monsoon (EAWM) was weaker than normal during the 2015 winter with an obvious phase transition from the strong to the weak at the end of December 2014. A warmer winter was experienced in most areas of China due to the effect of weaker EAWM. In association with the phase transition of EAWM, a reverse of temperature anomalies over China occurred simultaneously with negative temperature anomalies in December 2014 and positive temperature anomalies in January and February 2015. A super strong El Ni〖AKn~D〗o event occurred over the tropical Pacific Ocean, with the accumulative Ni〖AKn~D〗o Z index from May to November 2015 reaching to 23.0℃, was the strongest event on record. In addition, the remarkable Indian Ocean basinwide warming mode and the dipole mode with positive phases persisted since April of 2015. As a response of atmospheric circulation to the anomalous tropical oceanic condition, the western Pacific subtropical high intensified and extended further southward and westward, leading to less precipitation over North China and more precipitation over South China during summer. In 2015, onset of South China Sea summer monsoon was near normal and the ending time was 2 pentads later than normal with the intensity being weaker than normal.
Anomalies of oceanic and atmospheric circulations are analyzed and their impacts on temperature and precipitation anomalies of 2015 in China are investigated in this paper. It is found that the East Asian Winter Monsoon (EAWM) was weaker than normal during the 2015 winter with an obvious phase transition from the strong to the weak at the end of December 2014. A warmer winter was experienced in most areas of China due to the effect of weaker EAWM. In association with the phase transition of EAWM, a reverse of temperature anomalies over China occurred simultaneously with negative temperature anomalies in December 2014 and positive temperature anomalies in January and February 2015. A super strong El Ni〖AKn~D〗o event occurred over the tropical Pacific Ocean, with the accumulative Ni〖AKn~D〗o Z index from May to November 2015 reaching to 23.0℃, was the strongest event on record. In addition, the remarkable Indian Ocean basinwide warming mode and the dipole mode with positive phases persisted since April of 2015. As a response of atmospheric circulation to the anomalous tropical oceanic condition, the western Pacific subtropical high intensified and extended further southward and westward, leading to less precipitation over North China and more precipitation over South China during summer. In 2015, onset of South China Sea summer monsoon was near normal and the ending time was 2 pentads later than normal with the intensity being weaker than normal.
2016, 42(4):489-495.
DOI: 10.7519/j.issn.1000-0526.2016.04.013
Abstract:
The global average surface temperature in 2015 was about 0.76℃ higher than the mean value of 1961-1990, and it became the warmest year on record since 1850. In this year, the sea surface temperature (SST) in the CentralEastern Pacific was anomalously higher than normal, and the global ocean heat content broke the historical record. The maximum of Arctic sea ice extent during this year was at the lowest level on record while the Antarctic sea ice extent was still higher than normal. Affected by the external forcing factors and the persistent anomalous atmospheric circulation, notable extreme weather and climate events occurred worldwide, such as the frequent spring torrential rains in Southern Asia and the summer hot wave in Europe. Analysis shows that the anomalously warm SST in CentralEastern Pacific and Indian Ocean brought in the westward extension and enhancement of West Pacific subtropical high and the local active convection in Indian Peninsula, leading to more rainfalls in spring in Southern Asia. Moreover, the July hot wave in Europe resulted from the weakening of westerly and the establishment of meridional circulation which was related to the continual negative phase of Arctic Oscillation.
The global average surface temperature in 2015 was about 0.76℃ higher than the mean value of 1961-1990, and it became the warmest year on record since 1850. In this year, the sea surface temperature (SST) in the CentralEastern Pacific was anomalously higher than normal, and the global ocean heat content broke the historical record. The maximum of Arctic sea ice extent during this year was at the lowest level on record while the Antarctic sea ice extent was still higher than normal. Affected by the external forcing factors and the persistent anomalous atmospheric circulation, notable extreme weather and climate events occurred worldwide, such as the frequent spring torrential rains in Southern Asia and the summer hot wave in Europe. Analysis shows that the anomalously warm SST in CentralEastern Pacific and Indian Ocean brought in the westward extension and enhancement of West Pacific subtropical high and the local active convection in Indian Peninsula, leading to more rainfalls in spring in Southern Asia. Moreover, the July hot wave in Europe resulted from the weakening of westerly and the establishment of meridional circulation which was related to the continual negative phase of Arctic Oscillation.
2016, 42(4):496-506.
DOI: 10.7519/j.issn.1000-0526.2016.04.014
Abstract:
The precursory signals and their application in the shortterm climate prediction of the flood season in 2015 are reviewed in this paper. During the winter and spring in 2015, the thermal condition of the underlying surface exhibited some anomalous features. The El Ni〖AKn~D〗o event continued to develop and experienced a transition from the warm pool type to the cold tongue type. The warm sea surface temperature anomaly (SSTA) in the basin wide Indian Ocean continued to develop. The triple SSTA mode in the North Atlantic was in its positive phase. The sea ice extent was below normal in the Arctic and above normal in the Antarctic. The snow cover was below normal in Eurasia but above normal in the Tibetan Plateau. Among all the above features, the El Ni〖AKn~D〗o event and the warm tropical Indian Ocean were considered to be the most important factor for the prediction. In early April, based on the possible impact of the El Ni〖AKn~D〗o event and the dynamical model prediction, it was predicted that the East Asian summer monsoon would be weaker than normal and the precipitation would be more than normal in the southern part of East China and less in the northern part. In late May, a modification of the prediction was issued based on the possible impact from the warm SSTA in Indian Ocean and the weak crossequator flow in the South Hemisphere. Based on thorough investigation and analyses, the main features of the East Asian summer monsoon, the precipitation anomaly pattern in China and the major rainy seasons during summer were successfully predicted. Finally, this paper discusses some disadvantages of the prediction in summer 2015 as well.
The precursory signals and their application in the shortterm climate prediction of the flood season in 2015 are reviewed in this paper. During the winter and spring in 2015, the thermal condition of the underlying surface exhibited some anomalous features. The El Ni〖AKn~D〗o event continued to develop and experienced a transition from the warm pool type to the cold tongue type. The warm sea surface temperature anomaly (SSTA) in the basin wide Indian Ocean continued to develop. The triple SSTA mode in the North Atlantic was in its positive phase. The sea ice extent was below normal in the Arctic and above normal in the Antarctic. The snow cover was below normal in Eurasia but above normal in the Tibetan Plateau. Among all the above features, the El Ni〖AKn~D〗o event and the warm tropical Indian Ocean were considered to be the most important factor for the prediction. In early April, based on the possible impact of the El Ni〖AKn~D〗o event and the dynamical model prediction, it was predicted that the East Asian summer monsoon would be weaker than normal and the precipitation would be more than normal in the southern part of East China and less in the northern part. In late May, a modification of the prediction was issued based on the possible impact from the warm SSTA in Indian Ocean and the weak crossequator flow in the South Hemisphere. Based on thorough investigation and analyses, the main features of the East Asian summer monsoon, the precipitation anomaly pattern in China and the major rainy seasons during summer were successfully predicted. Finally, this paper discusses some disadvantages of the prediction in summer 2015 as well.
2016, 42(4):507-513.
DOI: 10.7519/j.issn.1000-0526.2016.04.015
Abstract:
During the autumn of 2015, the averaged surface air temperature in China was above normal. The mean precipitation in China was much more than normal, ranked as the 3rd since 1951. Thus, the autumn 2015 in China generally featured “warm and wet”. However, the temporal evolution of the precipitation of South and North China exhibited different characteristics. Driven by the different water vapor conditions, the South China was characterized by persistent precipitation, while North China featured several heavy rainfall events. By diagnosing the circulation anomaly, it was found that, the persistent anomalous rainfall over South China was associated with the forcing of the super strong El Ni〖AKn~〗o and warmer tropical Indian Ocean. The continued anomalous warming over the tropical eastern Pacific and Indian Ocean together strengthened the western Pacific subtropical high and pushed it westward. The anomalous southerlies along the western side of western Pacific subtropical high guided more water vapor from the South China Sea and the western Pacific to South China, causing the wetter autumn there. Meanwhile, the amplitudes of ridges and troughs in midlatitude regions were larger than normal, causing several strong cold air processes over North China, along with the water vapor transport from the East China Sea and South China Sea, and further leading to the anomalous precipitation in North China.
During the autumn of 2015, the averaged surface air temperature in China was above normal. The mean precipitation in China was much more than normal, ranked as the 3rd since 1951. Thus, the autumn 2015 in China generally featured “warm and wet”. However, the temporal evolution of the precipitation of South and North China exhibited different characteristics. Driven by the different water vapor conditions, the South China was characterized by persistent precipitation, while North China featured several heavy rainfall events. By diagnosing the circulation anomaly, it was found that, the persistent anomalous rainfall over South China was associated with the forcing of the super strong El Ni〖AKn~〗o and warmer tropical Indian Ocean. The continued anomalous warming over the tropical eastern Pacific and Indian Ocean together strengthened the western Pacific subtropical high and pushed it westward. The anomalous southerlies along the western side of western Pacific subtropical high guided more water vapor from the South China Sea and the western Pacific to South China, causing the wetter autumn there. Meanwhile, the amplitudes of ridges and troughs in midlatitude regions were larger than normal, causing several strong cold air processes over North China, along with the water vapor transport from the East China Sea and South China Sea, and further leading to the anomalous precipitation in North China.
2016, 42(4):514-520.
DOI: 10.7519/j.issn.1000-0526.2016.04.016
Abstract:
The following are the main characteristics of the general circulation of atmosphere in January 2016. There were three polar vortex centers which are stronger than normal years. The atmospheric circulation presented a great meridionality in middle latitude in Eurasia. The East Asia major trough and the south branch trough were stronger than those in average condition. The monthly mean precipitation was 25.7 mm around the country, 94.7% above the normal value, especially in Guangdong, Guangxi and Hunan it is 3.7 times more than normal, breaking the record of precipitation for the same periods since 1951. The monthly average temperature was -5.3℃, which is 0.3℃ lower than the normal years, but cold air activities appeared frequently. Totally, four cold air processes and five precipitation processes were reported. During 21-25 January, most part of China suffered from the strong cold surge which is characterized by a sharply drop in temperatures, extremely strong and widely affected area. The cold surge help many places of China build a new record for cold temperature. From 28 to 29 January, the southern part of China experienced a rarely seen severe rainstorm process.
The following are the main characteristics of the general circulation of atmosphere in January 2016. There were three polar vortex centers which are stronger than normal years. The atmospheric circulation presented a great meridionality in middle latitude in Eurasia. The East Asia major trough and the south branch trough were stronger than those in average condition. The monthly mean precipitation was 25.7 mm around the country, 94.7% above the normal value, especially in Guangdong, Guangxi and Hunan it is 3.7 times more than normal, breaking the record of precipitation for the same periods since 1951. The monthly average temperature was -5.3℃, which is 0.3℃ lower than the normal years, but cold air activities appeared frequently. Totally, four cold air processes and five precipitation processes were reported. During 21-25 January, most part of China suffered from the strong cold surge which is characterized by a sharply drop in temperatures, extremely strong and widely affected area. The cold surge help many places of China build a new record for cold temperature. From 28 to 29 January, the southern part of China experienced a rarely seen severe rainstorm process.
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ISSN:1000-0526 CN:11-2282/P