Most cited articles
2013, 36(1):37-46.
Abstract:
Based on the hourly precipitation observed by automatic weather stations(AWS) in China and retrieved from CMORPH(CPC MORPHing technique) satellite data,the merged precipitation product at hourly/0.1°lat/0.1°lon temporal-spatial resolution in China is developed through the two-step merging algorithm of PDF(probability density function) and OI(optimal interpolation).In this paper,the quality of merged precipitation product is assessed from the points of temporal-spatial characteristics of error,accuracy at different precipitation rates and cumulative times,merging effect at three station network densities and monitoring capability of the heavy rainfall.Results indicate that:1)The merged precipitation product effectively uses the advantages of AWS observations and satellite product of CMORPH,so it is more reasonable both at the precipitation amount and spatial distribution;2)The regional mean bias and root-mean-square error of the merged precipitation product are decreased remarkably,and they have a little change with time;3)The relative bias of merged precipitation product is -1.675%,less than 15% and about 30% for the medium(1.0—2.5 mm/h),medium to large(1.0—8.0 mm/h) and heavy rainfall(≥8.0 mm/h),respectively,and the product quality is improved further with the cumulative time increases.The merged precipitation product can capture the precipitation process very well and have a definite advantage in the quantitatively rainfall monitoring.
Based on the hourly precipitation observed by automatic weather stations(AWS) in China and retrieved from CMORPH(CPC MORPHing technique) satellite data,the merged precipitation product at hourly/0.1°lat/0.1°lon temporal-spatial resolution in China is developed through the two-step merging algorithm of PDF(probability density function) and OI(optimal interpolation).In this paper,the quality of merged precipitation product is assessed from the points of temporal-spatial characteristics of error,accuracy at different precipitation rates and cumulative times,merging effect at three station network densities and monitoring capability of the heavy rainfall.Results indicate that:1)The merged precipitation product effectively uses the advantages of AWS observations and satellite product of CMORPH,so it is more reasonable both at the precipitation amount and spatial distribution;2)The regional mean bias and root-mean-square error of the merged precipitation product are decreased remarkably,and they have a little change with time;3)The relative bias of merged precipitation product is -1.675%,less than 15% and about 30% for the medium(1.0—2.5 mm/h),medium to large(1.0—8.0 mm/h) and heavy rainfall(≥8.0 mm/h),respectively,and the product quality is improved further with the cumulative time increases.The merged precipitation product can capture the precipitation process very well and have a definite advantage in the quantitatively rainfall monitoring.
2013, 36(1):47-59.
Abstract:
Based on the conventional observations,NECP/NCAR reanalysis data,automatic weather station intensive observations and Doppler radar data,this paper contrasts the two typical squall line processes in Jiangsu and its surrounding areas on 28 Apirl 2006 and 14 June 2009.Results show that,prior to the two squall line processes,the warm advection obviously occurs in the lower troposphere and the cold advection appears in the middle-upper troposphere,which is helpful for the formation and development of stratification instability.During the movement and development of squall lines,a clear convergence line occurs in the surface wind field,which plays an important role in the triggering and maintenance of the squall lines.There are obvious differences of thermal and dynamic structures between the environment fields of the two processes.For the thermal structures,the former happens in spring when cold air is still strong and warm advection in the lower troposphere is one of main reasons of stratification instability,and the latter happens in summer when warm moist air is active and cold air invasion in middle-upper troposphere deserves attention greatly.The dynamic analysis shows that low level convergence and lifting conditions of the former are better than those of the latter.However,the thermal conditions of the latter are predominant,and it is easier to develop once the convection starts.
Based on the conventional observations,NECP/NCAR reanalysis data,automatic weather station intensive observations and Doppler radar data,this paper contrasts the two typical squall line processes in Jiangsu and its surrounding areas on 28 Apirl 2006 and 14 June 2009.Results show that,prior to the two squall line processes,the warm advection obviously occurs in the lower troposphere and the cold advection appears in the middle-upper troposphere,which is helpful for the formation and development of stratification instability.During the movement and development of squall lines,a clear convergence line occurs in the surface wind field,which plays an important role in the triggering and maintenance of the squall lines.There are obvious differences of thermal and dynamic structures between the environment fields of the two processes.For the thermal structures,the former happens in spring when cold air is still strong and warm advection in the lower troposphere is one of main reasons of stratification instability,and the latter happens in summer when warm moist air is active and cold air invasion in middle-upper troposphere deserves attention greatly.The dynamic analysis shows that low level convergence and lifting conditions of the former are better than those of the latter.However,the thermal conditions of the latter are predominant,and it is easier to develop once the convection starts.
2013, 36(3):257-266.
Abstract:
Based on the ensemble forecasting data of China Meteorological Administration(CMA),European Centre for Medium Range Weather Forecasts(ECMWF),Japan Meteorological Agency(JMA),U.S.National Centers for Environmental Prediction(NCEP),and United Kingdom Met Office(UKMO) in the TIGGE datasets,the multimodel ensemble forecasting techniques have been investigated.Results show that the multimodel ensemble forecasts are superior to that of the individual model.However,the improvement of multimodel ensemble forecast skill is different for different meteorological elements.The multimodel superensemble with running training period(R-SUP) has the best performance for surface air temperature in the Northern Hemisphere.For precipitation forecast in the Northern Hemisphere,the bias-removed ensemble mean(BREM) is more skillful and stable than every single model.In addition,the multimodel ensemble forecasting experiments of extreme weather event with freezing rain and snow over southern China during early 2008 have been conducted by using BREM with running training period(R-BREM).Taking root-mean-square errors(RMSEs) of ECMWF 96 h forecasts as the criterion,the forecast lead time of surface air temperature over the southeastern coast of China may be prolonged from 96 h to 192 h by using the R-BREM technique.And the threat scores(TS) of the light and moderate rain forecasts have been significantly improved except for some particular lead time.
Based on the ensemble forecasting data of China Meteorological Administration(CMA),European Centre for Medium Range Weather Forecasts(ECMWF),Japan Meteorological Agency(JMA),U.S.National Centers for Environmental Prediction(NCEP),and United Kingdom Met Office(UKMO) in the TIGGE datasets,the multimodel ensemble forecasting techniques have been investigated.Results show that the multimodel ensemble forecasts are superior to that of the individual model.However,the improvement of multimodel ensemble forecast skill is different for different meteorological elements.The multimodel superensemble with running training period(R-SUP) has the best performance for surface air temperature in the Northern Hemisphere.For precipitation forecast in the Northern Hemisphere,the bias-removed ensemble mean(BREM) is more skillful and stable than every single model.In addition,the multimodel ensemble forecasting experiments of extreme weather event with freezing rain and snow over southern China during early 2008 have been conducted by using BREM with running training period(R-BREM).Taking root-mean-square errors(RMSEs) of ECMWF 96 h forecasts as the criterion,the forecast lead time of surface air temperature over the southeastern coast of China may be prolonged from 96 h to 192 h by using the R-BREM technique.And the threat scores(TS) of the light and moderate rain forecasts have been significantly improved except for some particular lead time.
2014, 37(1):91-98.
Abstract:
Visibility variation trends from 1980 to 2005 have been constructed using four different statistical methods:Ridit analysis,cumulative percentiles,frequency of "very good" visibility,and annual and seasonal means.Improvements in visibility were experienced from 1980 to 1984.A decline trend can be observed after 1985 with some fluctuations in the process.In these 26 years,the mean daily visibility was 8.59 km with the maximum at 29.25 km and the minimum at 0.55 km,respectively.There were obvious seasonal and daily variation features in visibility.It was worst in winter and best in summer in one year while it was worst at 08:00 BST and best at 14:00 BST in one day.Visibility showed a positive correlation with wind speed and a negative correlation with relative humidity.However,temperature and atmospheric pressure showed comparatively little correlation with it.PM10 was the major pollutant in Nanjing.Curve estimation of daily mean PM10 mass concentration and the visibility presented a negative correlation and the coefficient was the largest in autumn and the smallest in summer.A regression model based on relative humidity,PM10,wind speed and temperature has been developed.There were seasonal differences in the coactions of air pollution and meteorological condition on visibility,which was worse in summer than that in the other three seasons.
Visibility variation trends from 1980 to 2005 have been constructed using four different statistical methods:Ridit analysis,cumulative percentiles,frequency of "very good" visibility,and annual and seasonal means.Improvements in visibility were experienced from 1980 to 1984.A decline trend can be observed after 1985 with some fluctuations in the process.In these 26 years,the mean daily visibility was 8.59 km with the maximum at 29.25 km and the minimum at 0.55 km,respectively.There were obvious seasonal and daily variation features in visibility.It was worst in winter and best in summer in one year while it was worst at 08:00 BST and best at 14:00 BST in one day.Visibility showed a positive correlation with wind speed and a negative correlation with relative humidity.However,temperature and atmospheric pressure showed comparatively little correlation with it.PM10 was the major pollutant in Nanjing.Curve estimation of daily mean PM10 mass concentration and the visibility presented a negative correlation and the coefficient was the largest in autumn and the smallest in summer.A regression model based on relative humidity,PM10,wind speed and temperature has been developed.There were seasonal differences in the coactions of air pollution and meteorological condition on visibility,which was worse in summer than that in the other three seasons.
2014, 37(1):119-126.
Abstract:
Paddy rice is one of the main crops in China.Timely information acquisition of rice planting area and spatial distribution at a large scale is of great significance in guiding rice production and regulating regional balance of supply and demand.In order to obtain paddy field area of Jiangsu Province,three types of vegetation indexes(including NDVI(normalized difference vegetation index),EVI(enhanced vegetation index),and LSWI(land surface water index)) are calculated by using the MODIS09A1 data from 2009 to 2011.Based on the temporal variation characteristics of EVI in different growth stages of rice,the key growth period of rice area extraction extracts is determined.According to the characteristics of rice transplanting period with high soil moisture,NDVI,EVI and LSWI are used to identify potential planting area of rice.The linear spectral mixture model is applied to decompose the mixed pixel of potential rice area,and the rice spatial distribution is obtained in Jiangsu Province from 2009 to 2011.Finally,selecting the typical sample area of rice,the rice planting area and spatial distribution are extracted by using HJ-1 CCD(30 m) data,and the results are used as reference data to verify the extraction accuracy.Meanwhile,the statistical rice planting area of Jiangsu Province from the statistical department is also used to verify the rice area.The error is within 10% by two methods of the statistical data and HJ-1 CCD(30 m) data.The research shows that it can more accurately extract a large range of rice planting area by using MODIS09A1 data and the linear spectral mixture model.
Paddy rice is one of the main crops in China.Timely information acquisition of rice planting area and spatial distribution at a large scale is of great significance in guiding rice production and regulating regional balance of supply and demand.In order to obtain paddy field area of Jiangsu Province,three types of vegetation indexes(including NDVI(normalized difference vegetation index),EVI(enhanced vegetation index),and LSWI(land surface water index)) are calculated by using the MODIS09A1 data from 2009 to 2011.Based on the temporal variation characteristics of EVI in different growth stages of rice,the key growth period of rice area extraction extracts is determined.According to the characteristics of rice transplanting period with high soil moisture,NDVI,EVI and LSWI are used to identify potential planting area of rice.The linear spectral mixture model is applied to decompose the mixed pixel of potential rice area,and the rice spatial distribution is obtained in Jiangsu Province from 2009 to 2011.Finally,selecting the typical sample area of rice,the rice planting area and spatial distribution are extracted by using HJ-1 CCD(30 m) data,and the results are used as reference data to verify the extraction accuracy.Meanwhile,the statistical rice planting area of Jiangsu Province from the statistical department is also used to verify the rice area.The error is within 10% by two methods of the statistical data and HJ-1 CCD(30 m) data.The research shows that it can more accurately extract a large range of rice planting area by using MODIS09A1 data and the linear spectral mixture model.
2013, 36(1):68-76.
Abstract:
In order to simulate meteorological parameters more accurately in the Planetary Boundary Layer(PBL) over complex terrain,the SRTM3 data from NASA was used in WRF model.With configuration of four PBL parameterization schemes(YSU scheme,ACM2 scheme,MYN scheme,and BL scheme) and two geographical data(SRTM3,GTOPO30),meteorological parameters in the PBL of the Mt Huang area during 24—25 April 2008 were evaluated.Temperature and dewpoint temperature of 2 m,wind speed of 10 m and water vapor distribution from simulation were contrasted to the observational data from 19 meteorological stations and 2 sounding stations in the Mt Huang area.Results show that YSU scheme was best for 2 m temperature simulation and ACM2 scheme was best for 2 m dewpoint temperature and 10 m wind speed simulation in the four PBL schemes with both geographical data;when SRTM3 data was used in WRF model,the mean RMSE of 2 m temperature simulated by the four PBL schemes were reduced by 3.79%(YSU scheme),2.48%(ACM2 scheme),3.8%(MYN scheme),and 0.87%(BL scheme), respectively;for 2 m dewpoint temperature,only the mean RMSE by MYN scheme was reduced by 0.59%,while the mean RMSE of YSU,BL and ACM2 schemes increased by 1.39%,0.49%,and 0.89%,respectively;as to 10 m wind speed,only the mean RMSE by ACM2 scheme was reduced by 2.28%,while the mean RMSE of YSU,MYN, and BL schemes increased by 0.22%,2.32%,and 2.45%,respectively;for the vertical distribution of water vapor from sounding report,all of the four PBL schemes can successfully simulate the vertical distribution tendency of water vapor,but all results turned out to be much moister;by using STRM3 data,the vertical distribution of water vapor simulated by ACM2 scheme was improved on low layer during some periods of time.
In order to simulate meteorological parameters more accurately in the Planetary Boundary Layer(PBL) over complex terrain,the SRTM3 data from NASA was used in WRF model.With configuration of four PBL parameterization schemes(YSU scheme,ACM2 scheme,MYN scheme,and BL scheme) and two geographical data(SRTM3,GTOPO30),meteorological parameters in the PBL of the Mt Huang area during 24—25 April 2008 were evaluated.Temperature and dewpoint temperature of 2 m,wind speed of 10 m and water vapor distribution from simulation were contrasted to the observational data from 19 meteorological stations and 2 sounding stations in the Mt Huang area.Results show that YSU scheme was best for 2 m temperature simulation and ACM2 scheme was best for 2 m dewpoint temperature and 10 m wind speed simulation in the four PBL schemes with both geographical data;when SRTM3 data was used in WRF model,the mean RMSE of 2 m temperature simulated by the four PBL schemes were reduced by 3.79%(YSU scheme),2.48%(ACM2 scheme),3.8%(MYN scheme),and 0.87%(BL scheme), respectively;for 2 m dewpoint temperature,only the mean RMSE by MYN scheme was reduced by 0.59%,while the mean RMSE of YSU,BL and ACM2 schemes increased by 1.39%,0.49%,and 0.89%,respectively;as to 10 m wind speed,only the mean RMSE by ACM2 scheme was reduced by 2.28%,while the mean RMSE of YSU,MYN, and BL schemes increased by 0.22%,2.32%,and 2.45%,respectively;for the vertical distribution of water vapor from sounding report,all of the four PBL schemes can successfully simulate the vertical distribution tendency of water vapor,but all results turned out to be much moister;by using STRM3 data,the vertical distribution of water vapor simulated by ACM2 scheme was improved on low layer during some periods of time.
2012, 35(2):197-204.
Abstract:
In order to investigate the variation characteristics of atmospheric particle pollution in the Olympic Village and evaluate the effect of pollution control measures on particle matter concentrations,the on-line measurements of particle mass concentration(PM10 and PM2.5) using TEOM were conducted on the rooftop of a six-floor building in the Institute of Remote Sensing Applications,Chinese Academy of Sciences,during both summer of 2007 and 2008.Results show that the average mass concentration of PM10 and PM2.5 during summer of 2007 are 153.9 and 71.2 μg·m-3,while the average mass concentration of PM10 and PM2.5 during summer of 2008 are 85.2 and 52.8 μg·m-3,respectively.Compared with the same period of one year before,the average mass concentration of PM10 and PM2.5 decrease by 44.5% and 25.1%,respectively,during the Olympic Games.Two typical particle pollution processes are selected to compare the variation difference of particle mass concentrations before and during the Olympic Games.The result shows that the relative humidity increasing and air masses transportation from south regions both together easily lead to the increasing of atmospheric particles,whereas the rainfall events and air mass transportation from north regions have a great effect on the scavenging of particle matter.In the similar weather conditions,the daily growth rate of fine particles in pollution accumulation process are 25.1 and 13.9 μg·m-3·d-1,while the daily growth rate of coarse particles are 20.8 and 2.2 μg·m-3·d-1,respectively,before and during Olympic Games.The daily growth rate of coarse and fine particles in pollution process during Olympic Games are significantly and slightly lower than those in pollution process before Olympic Games,which indicates that the implementation of pollution control measures during the Olympic Games has a great effect on the decreasing of particle matter,especially on the reduction of coarse particles.
In order to investigate the variation characteristics of atmospheric particle pollution in the Olympic Village and evaluate the effect of pollution control measures on particle matter concentrations,the on-line measurements of particle mass concentration(PM10 and PM2.5) using TEOM were conducted on the rooftop of a six-floor building in the Institute of Remote Sensing Applications,Chinese Academy of Sciences,during both summer of 2007 and 2008.Results show that the average mass concentration of PM10 and PM2.5 during summer of 2007 are 153.9 and 71.2 μg·m-3,while the average mass concentration of PM10 and PM2.5 during summer of 2008 are 85.2 and 52.8 μg·m-3,respectively.Compared with the same period of one year before,the average mass concentration of PM10 and PM2.5 decrease by 44.5% and 25.1%,respectively,during the Olympic Games.Two typical particle pollution processes are selected to compare the variation difference of particle mass concentrations before and during the Olympic Games.The result shows that the relative humidity increasing and air masses transportation from south regions both together easily lead to the increasing of atmospheric particles,whereas the rainfall events and air mass transportation from north regions have a great effect on the scavenging of particle matter.In the similar weather conditions,the daily growth rate of fine particles in pollution accumulation process are 25.1 and 13.9 μg·m-3·d-1,while the daily growth rate of coarse particles are 20.8 and 2.2 μg·m-3·d-1,respectively,before and during Olympic Games.The daily growth rate of coarse and fine particles in pollution process during Olympic Games are significantly and slightly lower than those in pollution process before Olympic Games,which indicates that the implementation of pollution control measures during the Olympic Games has a great effect on the decreasing of particle matter,especially on the reduction of coarse particles.
2013, 36(1):20-28.
Abstract:
By using GODAS monthly mixed layer depth(MLD) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of MLD are analyzed over the north Pacific,along with the influences of MLD interannual anomaly on summer rainfall in China discussed.The results show that:1) The MLD is the deepest over the latitudes from 30 to 40°N and is larger in winter and spring than in summer and autumn.2) The interannual anomaly is most prominent over the middle part of the north Pacific near the international date line in four seasons;but only the MLD anomaly is somewhat related to ENSO in summer,and MLD is of interdecadal anomaly characteristics in autumn,winter and spring.3)When MLD increases over western and middle part of the north and central area of Pacific in the previous winter,the precipitation may decrease over the part of the lower Yellow River,Huang-huai,Jiang-huai and to the south of the Yangtze River reaches(except the south of Guangxi) and the precipitation may increase in He-tao,east part of Neimeng and most part of Northeast China in the following year.
By using GODAS monthly mixed layer depth(MLD) and 160-station monthly precipitation data in China,the seasonal and interannual characteristics of MLD are analyzed over the north Pacific,along with the influences of MLD interannual anomaly on summer rainfall in China discussed.The results show that:1) The MLD is the deepest over the latitudes from 30 to 40°N and is larger in winter and spring than in summer and autumn.2) The interannual anomaly is most prominent over the middle part of the north Pacific near the international date line in four seasons;but only the MLD anomaly is somewhat related to ENSO in summer,and MLD is of interdecadal anomaly characteristics in autumn,winter and spring.3)When MLD increases over western and middle part of the north and central area of Pacific in the previous winter,the precipitation may decrease over the part of the lower Yellow River,Huang-huai,Jiang-huai and to the south of the Yangtze River reaches(except the south of Guangxi) and the precipitation may increase in He-tao,east part of Neimeng and most part of Northeast China in the following year.
2013, 36(2):217-228.
Abstract:
Based on the observations of 63 conventional meteorological stations and the investigated data of food-crops production in Jiangsu Province from 1986 to 2010,this paper studied the characteristics of climate change on three time scales in north,central and south Jiangsu,and the whole province.Based on the one-dimensional linear regression equation with the bootstrap resampling method,this paper studied the responses of the food-crops production to climate changes on the three time scales of crop-year(from November to October the next year),the growth seasons of summer(from Novemeber to May the next year) and autumn(from June to October) crops,and month.The influences of climate changes on the food-crops yield and the contributions of each climate factor in the past 25 years were quantitatively estimated.Results show that:1)In north,central and south Jiangsu,and the whole province,the climate factors are different on the time scales of crop-year,the growth season of summer and autumn crops and month,with some spatial-temporal differences.Under the combined impacts of the developing agricultural managements and technologies,and climate change,the food-crops yield per hectare in the four study areas increases significantly(p>0.01),with increasing trend of 66.89 kg·hm-2·a-1 in the whole province.2)Except that the response of the food-crops yield in south Jiangsu to climate change on the time scale of crop-year is not significant,the negative response of the food-crops yield to precipitation(the food-crops yield decreases when precipitation increases,and v.v.) can be found in the four study areas on the three time scales,indicating that precipitation variation plays an important role in the food-crops production.When precipitation increases(decreases),the food-crops yield in north and south Jiangsu,and Jiangsu decreases (increases),with the mean rates of 0.19%·(10 mm)-1,0.09%·(10 mm)-1 and 0.11%·(10 mm)-1,respectively.3)Results of the three models show that the food-crops production in north and south Jiangsu,and Jiangsu all decreases due to climate change.Results of Model-C established by monthly climate factors reveal that climate change leads to the food-crops yield per hectare(total production) decrease of -6.51%·(10 a)-1(-11.28×108 kg·(10 a)-1),-3.27%·(10 a)-1(-2.36×108 kg·(10 a)-1) and-1.34%·(10 a)-1(-4.45×108 kg·(10 a)-1) in north and south Jiangsu,and Jiangsu,respectively.Additionally,it is very necessary and critical to pay enough attention on the effects of monthly climate change in order to completely and systematically evaluate effects of climate change on food-crops production.
Based on the observations of 63 conventional meteorological stations and the investigated data of food-crops production in Jiangsu Province from 1986 to 2010,this paper studied the characteristics of climate change on three time scales in north,central and south Jiangsu,and the whole province.Based on the one-dimensional linear regression equation with the bootstrap resampling method,this paper studied the responses of the food-crops production to climate changes on the three time scales of crop-year(from November to October the next year),the growth seasons of summer(from Novemeber to May the next year) and autumn(from June to October) crops,and month.The influences of climate changes on the food-crops yield and the contributions of each climate factor in the past 25 years were quantitatively estimated.Results show that:1)In north,central and south Jiangsu,and the whole province,the climate factors are different on the time scales of crop-year,the growth season of summer and autumn crops and month,with some spatial-temporal differences.Under the combined impacts of the developing agricultural managements and technologies,and climate change,the food-crops yield per hectare in the four study areas increases significantly(p>0.01),with increasing trend of 66.89 kg·hm-2·a-1 in the whole province.2)Except that the response of the food-crops yield in south Jiangsu to climate change on the time scale of crop-year is not significant,the negative response of the food-crops yield to precipitation(the food-crops yield decreases when precipitation increases,and v.v.) can be found in the four study areas on the three time scales,indicating that precipitation variation plays an important role in the food-crops production.When precipitation increases(decreases),the food-crops yield in north and south Jiangsu,and Jiangsu decreases (increases),with the mean rates of 0.19%·(10 mm)-1,0.09%·(10 mm)-1 and 0.11%·(10 mm)-1,respectively.3)Results of the three models show that the food-crops production in north and south Jiangsu,and Jiangsu all decreases due to climate change.Results of Model-C established by monthly climate factors reveal that climate change leads to the food-crops yield per hectare(total production) decrease of -6.51%·(10 a)-1(-11.28×108 kg·(10 a)-1),-3.27%·(10 a)-1(-2.36×108 kg·(10 a)-1) and-1.34%·(10 a)-1(-4.45×108 kg·(10 a)-1) in north and south Jiangsu,and Jiangsu,respectively.Additionally,it is very necessary and critical to pay enough attention on the effects of monthly climate change in order to completely and systematically evaluate effects of climate change on food-crops production.
2012, 35(4):477-486.
Abstract:
Three-dimensional 4-day backward trajectories arriving in Lanzhou at 500m high were calculated every 6 h by using HYSPLIT-4 trajectory model in spring of 2001 to 2008.The 8 years were divided into two categories:high dust year (2001,2002,2004 and 2006) and low dust year (2003,2005,2007 and 2008).Cluster analysis,potential source contribution function (PSCF) model,and concentration-weighted trajectory (CWT) method were used to evaluate the transportation pathways and potential source regions of Lanzhou PM10 pollution in spring.Results indicate that the western and northwestern pathways,respectively accounting for 33% and 19.4% of all trajectories,were major pathways leading to high springtime PM10 loadings in Lanzhou in 2001,2002,2004 and 2006.However,the major pathways were the western and the northern pathways in 2003,2005,2007 and 2008,accounting for 23.6% and 18%,respectively.There were six potential source regions that had effect on PM10concentration in Lanzhou,including Tarim Basin and Turpan Basin in Xinjiang,Qaidam Basin in Qinghai,Hexi Corridor in Gansu Province,the desert and gobi area in central and western Inner Mongolia.
Three-dimensional 4-day backward trajectories arriving in Lanzhou at 500m high were calculated every 6 h by using HYSPLIT-4 trajectory model in spring of 2001 to 2008.The 8 years were divided into two categories:high dust year (2001,2002,2004 and 2006) and low dust year (2003,2005,2007 and 2008).Cluster analysis,potential source contribution function (PSCF) model,and concentration-weighted trajectory (CWT) method were used to evaluate the transportation pathways and potential source regions of Lanzhou PM10 pollution in spring.Results indicate that the western and northwestern pathways,respectively accounting for 33% and 19.4% of all trajectories,were major pathways leading to high springtime PM10 loadings in Lanzhou in 2001,2002,2004 and 2006.However,the major pathways were the western and the northern pathways in 2003,2005,2007 and 2008,accounting for 23.6% and 18%,respectively.There were six potential source regions that had effect on PM10concentration in Lanzhou,including Tarim Basin and Turpan Basin in Xinjiang,Qaidam Basin in Qinghai,Hexi Corridor in Gansu Province,the desert and gobi area in central and western Inner Mongolia.
2014, 37(1):75-81.
Abstract:
After the homogeneity test and correction,the meteorological data from 96 observation stations in Hunan province during 1960—2010 were used to analyze the climate change facts there.The results showed that getting warm was the main characteristic in climate change in Hunan,which was consistent with the global trend.The warming tendency in Hunan also presented seasonal and regional differences:the linear warming trend was significant in winter,spring and autumn and the most significant warming region appeared in northern areas;the factors sensitive to warming were closely related to temperature such as seasonal mean temperature,annual mean minimal temperature and active accumulated temperature.The abrupt change times of temperature presented a good logical relation;the linear trend of precipitation in Hunan was not significant but it presented regional differences and the extreme preicipitation events was increasing.There was an increasing trend in precipitation in eastern areas of Hunan and the annual days with daily precipitation of more than 100 mm were increasing significantly.The annual sunshine hours,annual mean wind speed and annual mean relative humidity in Hunan presented a significantly decresing trend in recent 61 years.
After the homogeneity test and correction,the meteorological data from 96 observation stations in Hunan province during 1960—2010 were used to analyze the climate change facts there.The results showed that getting warm was the main characteristic in climate change in Hunan,which was consistent with the global trend.The warming tendency in Hunan also presented seasonal and regional differences:the linear warming trend was significant in winter,spring and autumn and the most significant warming region appeared in northern areas;the factors sensitive to warming were closely related to temperature such as seasonal mean temperature,annual mean minimal temperature and active accumulated temperature.The abrupt change times of temperature presented a good logical relation;the linear trend of precipitation in Hunan was not significant but it presented regional differences and the extreme preicipitation events was increasing.There was an increasing trend in precipitation in eastern areas of Hunan and the annual days with daily precipitation of more than 100 mm were increasing significantly.The annual sunshine hours,annual mean wind speed and annual mean relative humidity in Hunan presented a significantly decresing trend in recent 61 years.
2014, 37(2):163-174.
Abstract:
Threshold value of extreme precipitation of each station was confirmed through the percentile method based on the daily precipitation in Shandong Province from 1971 to 1999.Based on the threshold value,the 39 extreme precipitation events in Shandong Province from 2000 to 2009 were classified to five conceptual models,including upper trough,subtropical high periphery,shear line,cyclone and tropical cyclone types.Results show that the heavy rain area of the shear line,cyclone and tropical cyclone types is often larger,and that of the upper trough and subtropical high periphery types is generally scattered.There is low level jet in all five types,and the heavy rain area generally lies between 700 hPa and 850 hPa shear lines(or trough lines),at the wind speed convergence on the left side of low level jet.There is cold air in the upper trough type,the subtropical peripheral type and the shear line type 1,and the heavy rain area is located in front of 850 hPa cold temperature trough.For the five types,the mechanisms of extreme precipitation are different,and the configurations between heavy rain area and θse are not same.
Threshold value of extreme precipitation of each station was confirmed through the percentile method based on the daily precipitation in Shandong Province from 1971 to 1999.Based on the threshold value,the 39 extreme precipitation events in Shandong Province from 2000 to 2009 were classified to five conceptual models,including upper trough,subtropical high periphery,shear line,cyclone and tropical cyclone types.Results show that the heavy rain area of the shear line,cyclone and tropical cyclone types is often larger,and that of the upper trough and subtropical high periphery types is generally scattered.There is low level jet in all five types,and the heavy rain area generally lies between 700 hPa and 850 hPa shear lines(or trough lines),at the wind speed convergence on the left side of low level jet.There is cold air in the upper trough type,the subtropical peripheral type and the shear line type 1,and the heavy rain area is located in front of 850 hPa cold temperature trough.For the five types,the mechanisms of extreme precipitation are different,and the configurations between heavy rain area and θse are not same.
2014, 37(1):19-27.
Abstract:
Using the three dimensional observation test data of urban heat island(UHI) in Nanjing in summer 2010,spatial and temporal distribution characteristics of urban heat island under typical weather conditions were analyzed.The results showed that daily mean UHI intensity on sunny days was over 1 ℃ in Nanjing in summer.UHI intensity was stronger and more stable during nighttime than that in daytime,with UHI distribution displaying directional characteristic and corresponding well to urban land-use conditions.During daytime,mixed layer in urban areas developed faster and was higher than that in the suburbs.During nighttime,there existed a long lasting convective mixed layer at low altitude in the city due to the unstable atmospheric stratification and the roughness of the underlying surface,which was as thick as more than 250 m.Owing to the storage of a large amount of heat and strong turbulent transport in urban underlying surface,heat island came into being in urban boundary layer,with UHI intensity decreasing with height.Heat island in boundary layer extended up to 900 m in daytime and maintained at 300 m at nighttime.
Using the three dimensional observation test data of urban heat island(UHI) in Nanjing in summer 2010,spatial and temporal distribution characteristics of urban heat island under typical weather conditions were analyzed.The results showed that daily mean UHI intensity on sunny days was over 1 ℃ in Nanjing in summer.UHI intensity was stronger and more stable during nighttime than that in daytime,with UHI distribution displaying directional characteristic and corresponding well to urban land-use conditions.During daytime,mixed layer in urban areas developed faster and was higher than that in the suburbs.During nighttime,there existed a long lasting convective mixed layer at low altitude in the city due to the unstable atmospheric stratification and the roughness of the underlying surface,which was as thick as more than 250 m.Owing to the storage of a large amount of heat and strong turbulent transport in urban underlying surface,heat island came into being in urban boundary layer,with UHI intensity decreasing with height.Heat island in boundary layer extended up to 900 m in daytime and maintained at 300 m at nighttime.
2014, 37(5):529-540.
DOI: 10.13878/j.cnki.dqkxxb.20130512001
Abstract:
This paper evaluates the future projection of heavy rainfall events in the middle and lower reaches of the Yangtze River valley based on outputs of eight coupled models attending the Coupled Model Intercomparison Project phase 5(CMIP5) from IPCC AR5.The experiments under different representative concentration pathways(RCPs) are compared with each other,and with the previous CMIP3 experiments as well.The outputs from the historical simulation of CMIP5 are also utilized as a base to derive future trends.The results suggest an agreement among all the CMIP5 models,in that both the strength and the occurrence frequency of heavy rainfall events are projected to increase in the 21st century relative to the last twenty years of the 20th century(1980—1999).In contrast,the strength increase in the east of the region is even greater than that in the west.Besides,the interannual variability of heavy rainfall events is also projected to enhance in the future.As for different RCPs,the projected increases in the strength and occurrence frequency of heavy rainfall events in RCP2.6 and RCP8.5 are greater than those in RCP4.5.In comparison to CMIP3,the projected increases in the strength and occurrence frequency are even larger,albeit a significant difference in the spatial distribution in the latter projection.The projected maximum increase in the rainfall amplitude in CMIP3 is located in the central region,while it is in the east of the region in CMIP5.
This paper evaluates the future projection of heavy rainfall events in the middle and lower reaches of the Yangtze River valley based on outputs of eight coupled models attending the Coupled Model Intercomparison Project phase 5(CMIP5) from IPCC AR5.The experiments under different representative concentration pathways(RCPs) are compared with each other,and with the previous CMIP3 experiments as well.The outputs from the historical simulation of CMIP5 are also utilized as a base to derive future trends.The results suggest an agreement among all the CMIP5 models,in that both the strength and the occurrence frequency of heavy rainfall events are projected to increase in the 21st century relative to the last twenty years of the 20th century(1980—1999).In contrast,the strength increase in the east of the region is even greater than that in the west.Besides,the interannual variability of heavy rainfall events is also projected to enhance in the future.As for different RCPs,the projected increases in the strength and occurrence frequency of heavy rainfall events in RCP2.6 and RCP8.5 are greater than those in RCP4.5.In comparison to CMIP3,the projected increases in the strength and occurrence frequency are even larger,albeit a significant difference in the spatial distribution in the latter projection.The projected maximum increase in the rainfall amplitude in CMIP3 is located in the central region,while it is in the east of the region in CMIP5.
2015, 38(4):473-482.
DOI: 10.13878/j.cnki.dqkxxb.20140102010
Abstract:
Total 109 precipitation samples were collected in north suburb of Nanjing from March to June 2011.In order to investigate the chemistry characteristics of precipitation,the concentration of water-soluble ions were analyzed and the air mass sources of precipitation were also discussed using the back trajectory model.Results show that the precipitation is mainly controlled by southern and northern air masses,and the concentrations of major ions from precipitation of northern air masses are higher than those from southern.The sea salt tracer method and the correlation analysis indicate that NO3- and SO42- are mainly from coal burning,industrial emissions and vehicle exhaust emissions.Ca2+ and Cl- mainly derive from crustal and marine sources,respectively.K+ and Mg2+ are both from marine and terrestrial sources,while the terrestrial contribution of Mg2+ is dominant,and the impact of marine on K+ is lower than on Mg2+.Due to the scavenging process,the concentrations of different ions and the enrichment factors of main ions in the early period of precipitation are higher than those in the whole period of precipitation,which are attributed to the main contribution of local pollution sources.
Total 109 precipitation samples were collected in north suburb of Nanjing from March to June 2011.In order to investigate the chemistry characteristics of precipitation,the concentration of water-soluble ions were analyzed and the air mass sources of precipitation were also discussed using the back trajectory model.Results show that the precipitation is mainly controlled by southern and northern air masses,and the concentrations of major ions from precipitation of northern air masses are higher than those from southern.The sea salt tracer method and the correlation analysis indicate that NO3- and SO42- are mainly from coal burning,industrial emissions and vehicle exhaust emissions.Ca2+ and Cl- mainly derive from crustal and marine sources,respectively.K+ and Mg2+ are both from marine and terrestrial sources,while the terrestrial contribution of Mg2+ is dominant,and the impact of marine on K+ is lower than on Mg2+.Due to the scavenging process,the concentrations of different ions and the enrichment factors of main ions in the early period of precipitation are higher than those in the whole period of precipitation,which are attributed to the main contribution of local pollution sources.
2017, 40(2):145-157.
DOI: 10.13878/j.cnki.dqkxxb.20160405001
Abstract:
The ensemble forecast technique is a practical solution to the uncertainty problem of numerical weather prediction.At present,researchers around the world tend to focus on the Regional Ensemble Forecast(REF),which aims at the improvement of regional high impact weather forecast.As various uncertainty resources exist for meso-scale and small-scale weather phenomena,regional model simulation is a very complicated issue,thus how to generate effective perturbations for REF is a hot topic involving many technical difficulties.In the present paper,the progress of REF research is reviewed in terms of initial condition perturbation,model perturbation and lateral boundary condition perturbation,and the trends of methods related to these aspects are also presented.The results presented show the following:for initial condition perturbation,the mainstream methods include dynamical downscaling,using traditional methods developed from Global Ensemble to generate perturbations for REF,as well as some methods specifically designed for REF.All of these methods are characterized by some advantages and some shortcomings,as downscaling a lack of small scale and other components leads to the generation of insufficient large-scale uncertainty information.In addition,research on the REF initial condition perturbation has only begun to explore more effective methods such as blending,which consider not only sufficiently small-scale uncertainty,but also sufficiently large-scale uncertainty.Finally,the inconsistency problem between initial state and lateral boundary can also be ameliorated.Model perturbation is another important aspect for REF.This technique mostly perturbs model physics,such as multi-physics combination and stochastically perturb model physics.It has been reported that the multi-physics combination is quite simple and can effectively improve the ensemble spread of REF,while using the stochastic method to perturb model physics has greater scientific significance,thus this type of perturbation method has become the trend of model physics perturbations.Furthermore,multi-model combination is another practical method of model perturbation.Related studies have been carried out,the results of which show that this method possesses stronger skill than a single model ensemble,especially when a multi-model ensemble is applied to meso-scale severe weather forecast,such as with a Tropical Cyclone.As REF systems are constructed based on the regional models,the uncertainties originating from lateral boundary conditions cannot be ignored.Lateral boundary condition perturbation schemes mainly use large-scale ensembles,such as Global Ensemble Forecast Products,to provide different lateral boundary conditions for REF.Studies have proven that this method can achieve the goal of perturbing the lateral boundary condition of REF,and lateral boundary condition perturbation is found to aid in amplifying the ensemble spread of REF for long-range forecast lead times.In addition,the ensemble forecast skill can also benefit from lateral boundary perturbation.Although the perturbation techniques for REF have already led to some fruitful achievements,much work is still needed,and all of the methods related to initial condition perturbations,model perturbations and lateral boundary condition perturbations are still under development.It can be predicted that,as the REF perturbation methods continue to improve,the REF will become increasingly more effective,and will play a more important role in operational numerical weather prediction centers.
The ensemble forecast technique is a practical solution to the uncertainty problem of numerical weather prediction.At present,researchers around the world tend to focus on the Regional Ensemble Forecast(REF),which aims at the improvement of regional high impact weather forecast.As various uncertainty resources exist for meso-scale and small-scale weather phenomena,regional model simulation is a very complicated issue,thus how to generate effective perturbations for REF is a hot topic involving many technical difficulties.In the present paper,the progress of REF research is reviewed in terms of initial condition perturbation,model perturbation and lateral boundary condition perturbation,and the trends of methods related to these aspects are also presented.The results presented show the following:for initial condition perturbation,the mainstream methods include dynamical downscaling,using traditional methods developed from Global Ensemble to generate perturbations for REF,as well as some methods specifically designed for REF.All of these methods are characterized by some advantages and some shortcomings,as downscaling a lack of small scale and other components leads to the generation of insufficient large-scale uncertainty information.In addition,research on the REF initial condition perturbation has only begun to explore more effective methods such as blending,which consider not only sufficiently small-scale uncertainty,but also sufficiently large-scale uncertainty.Finally,the inconsistency problem between initial state and lateral boundary can also be ameliorated.Model perturbation is another important aspect for REF.This technique mostly perturbs model physics,such as multi-physics combination and stochastically perturb model physics.It has been reported that the multi-physics combination is quite simple and can effectively improve the ensemble spread of REF,while using the stochastic method to perturb model physics has greater scientific significance,thus this type of perturbation method has become the trend of model physics perturbations.Furthermore,multi-model combination is another practical method of model perturbation.Related studies have been carried out,the results of which show that this method possesses stronger skill than a single model ensemble,especially when a multi-model ensemble is applied to meso-scale severe weather forecast,such as with a Tropical Cyclone.As REF systems are constructed based on the regional models,the uncertainties originating from lateral boundary conditions cannot be ignored.Lateral boundary condition perturbation schemes mainly use large-scale ensembles,such as Global Ensemble Forecast Products,to provide different lateral boundary conditions for REF.Studies have proven that this method can achieve the goal of perturbing the lateral boundary condition of REF,and lateral boundary condition perturbation is found to aid in amplifying the ensemble spread of REF for long-range forecast lead times.In addition,the ensemble forecast skill can also benefit from lateral boundary perturbation.Although the perturbation techniques for REF have already led to some fruitful achievements,much work is still needed,and all of the methods related to initial condition perturbations,model perturbations and lateral boundary condition perturbations are still under development.It can be predicted that,as the REF perturbation methods continue to improve,the REF will become increasingly more effective,and will play a more important role in operational numerical weather prediction centers.
17 Reconstruction of equatorial Pacific SST anomaly indices for two types of ENSO during boreal winter
2016, 39(4):455-467.
DOI: 10.13878/j.cnki.dqkxxb.20150123001
Abstract:
ENSO is the strongest interannual variability in our climate system.Recently,it has been found to vary as two types in spatial terms;the Central Pacific (CP) type,whose SST anomalies (SSTAs) are strongest in the central Pacific;and the Eastern Pacific (EP) type,characterized by SSTAs being strongest in the eastern equatorial Pacific.These two types of El Niño involve different teleconnections and climatic impacts,as the intensity and location of their associated SST-induced heating are different.Many studies have pointed out that CP El Niño events have increased in frequency in recent decades.Several kinds of indices have been designed for different types of El Niño events.For instance,the El Niño Modoki index (EMI) captures the second EOF pattern of equatorial Pacific SST anomalies.Another somewhat complicated index pair called the Central and Eastern Pacific Index (CPI/EPI),which is also an EOF-based index but with the SSTA related to the Niño1+2 or Niño4 index removed,has also been put forward.The most striking difference between the two types of El Niño is the longitudinal displacement of maximum anomalous SST along the equator in their mature stages.Motivated by this method of classification,we redefined two indices of SST anomalies,i.e.,ICP and IEP,for describing CP and EP El Niño/La Niña events and their interactions during boreal winter,by using both NCEP/NCAR reanalysis data and SST data from the Hadley Centre,for the period 1963-2013.This index pair was reconstructed based on the function for the CP pattern that changes with longitude and is perpendicular to the function for the EP pattern.Compared to other El Niño indices proposed previously,we found that the new indices can be used for better separating EP-type ENSO events from CP-type events,both spatially and temporally.The major features of air-sea coupling in the tropical Pacific related to CP-and EP-type events were investigated using the two new indices.It was found that these two distinct types of ENSO events demonstrate different periodic variation.Specifically,although they both exhibit 2-7- and 10-15-year oscillations in the tropical SSTA field,the decadal (10-15-year) variations for CP-type ENSO events are more dominant.It was also found that the anomalous warming center of CP-type El Niño appears in the central equatorial Pacific as expected,which is quite different from canonical EP-type El Niño events with their largest warm centers located in the eastern equatorial Pacific.Consequently,during CP-type events,the ascending branch of Walker circulation shifts farther west than normal,resulting in rainfall intensification mainly over the central tropical Pacific.However,when EP-type El Niño events occur,anomalous ascending motion is observed in the eastern equatorial Pacific,along with increased rainfall.Interestingly,during boreal winter,both types of El Niño can affect the Maritime Continent,but the CP type more strongly.Specifically,the Maritime Continent receives less than normal rainfall.Both of the reconstructed SSTA indices developed in this study are expected to be highly useful for monitoring ENSO events,and helpful in improving our understanding of the similarities and differences in the influence of CP-and EP-type ENSO events on climate variation at the global and regional (particularly East Asia) scale.
ENSO is the strongest interannual variability in our climate system.Recently,it has been found to vary as two types in spatial terms;the Central Pacific (CP) type,whose SST anomalies (SSTAs) are strongest in the central Pacific;and the Eastern Pacific (EP) type,characterized by SSTAs being strongest in the eastern equatorial Pacific.These two types of El Niño involve different teleconnections and climatic impacts,as the intensity and location of their associated SST-induced heating are different.Many studies have pointed out that CP El Niño events have increased in frequency in recent decades.Several kinds of indices have been designed for different types of El Niño events.For instance,the El Niño Modoki index (EMI) captures the second EOF pattern of equatorial Pacific SST anomalies.Another somewhat complicated index pair called the Central and Eastern Pacific Index (CPI/EPI),which is also an EOF-based index but with the SSTA related to the Niño1+2 or Niño4 index removed,has also been put forward.The most striking difference between the two types of El Niño is the longitudinal displacement of maximum anomalous SST along the equator in their mature stages.Motivated by this method of classification,we redefined two indices of SST anomalies,i.e.,ICP and IEP,for describing CP and EP El Niño/La Niña events and their interactions during boreal winter,by using both NCEP/NCAR reanalysis data and SST data from the Hadley Centre,for the period 1963-2013.This index pair was reconstructed based on the function for the CP pattern that changes with longitude and is perpendicular to the function for the EP pattern.Compared to other El Niño indices proposed previously,we found that the new indices can be used for better separating EP-type ENSO events from CP-type events,both spatially and temporally.The major features of air-sea coupling in the tropical Pacific related to CP-and EP-type events were investigated using the two new indices.It was found that these two distinct types of ENSO events demonstrate different periodic variation.Specifically,although they both exhibit 2-7- and 10-15-year oscillations in the tropical SSTA field,the decadal (10-15-year) variations for CP-type ENSO events are more dominant.It was also found that the anomalous warming center of CP-type El Niño appears in the central equatorial Pacific as expected,which is quite different from canonical EP-type El Niño events with their largest warm centers located in the eastern equatorial Pacific.Consequently,during CP-type events,the ascending branch of Walker circulation shifts farther west than normal,resulting in rainfall intensification mainly over the central tropical Pacific.However,when EP-type El Niño events occur,anomalous ascending motion is observed in the eastern equatorial Pacific,along with increased rainfall.Interestingly,during boreal winter,both types of El Niño can affect the Maritime Continent,but the CP type more strongly.Specifically,the Maritime Continent receives less than normal rainfall.Both of the reconstructed SSTA indices developed in this study are expected to be highly useful for monitoring ENSO events,and helpful in improving our understanding of the similarities and differences in the influence of CP-and EP-type ENSO events on climate variation at the global and regional (particularly East Asia) scale.
2016, 39(4):480-489.
DOI: 10.13878/j.cnki.dqkxxb.20140413001
Abstract:
Continuous autumn rain is long in duration,meaning it can easily cause crop mold and other adverse effects relating to daily life and industrial and agricultural production.In order to mitigate such losses caused by continuous autumn rain,it is important to study in depth the climate characteristics of continuous autumn rain and its causes.The present study does this based on the daily rainfall and sunshine data of 753 meteorological stations in China in autumn (September-November) from 1961 to 2010,along with NCEP/NCAR reanalysis data for the period 1948-2010.After defining continuous autumn rain in China,its climate characteristics for different levels (5-7 d,8-10 d,and 11 d and above) are analyzed.Based on a general survey of regions where continuous autumn rain was found to happen often during 1961-2010,China is divided into four regions of continuous autumn rain;namely,North China,Southwest China,the Changjiang-Huaihe basin,and South China,where representative stations are Xingtai (Hebei Province),Wufeng (Hubei Province),Gushi (Henan Province) and Yongan (Fujian Province),respectively.The circulation characteristics of continuous autumn rain and continuous autumn rain of different levels in North China are also analyzed.The results show that: (1)The accumulated frequency of continuous autumn rain and continuous autumn rain of different levels mainly concentrates in the mid-upper reaches of the Yangtze River during 1961-2010,and is very small in the areas north to the Yellow River.With an increase in the level of rain,the high-frequency areas move from southeast to southwest.The frequency standard deviation is similar to the frequency of continuous autumn rain and continuous autumn rain of different levels. (2)During the continuous autumn rain and continuous autumn rain of different levels in North China,in the 500 hPa geopotential height field,the northern cold air is guided to the south by northerly flow after the East Asian trough,and southern warm air is guided to the north by southerly flow on the west side of the subtropical high.The cold and warm air masses meet over North China,which is beneficial to the formation of the continuous rain weather.Positive height anomalies are located over North China,but negative height anomalies are located in the east and west sides of North China. (3)The circulation patterns feature a number of differences among the different levels of continuous autumn rain.The East Asian trough and Urals ridge are the strongest and located farthest east for the 8-10 d level,followed by the 11 d and above level,and finally the 5-7 d level.The trough is most obvious over Lake Balkhash for the 8-10 d level. (4)In the 850-hPa wind field,the enhanced southern and northern air streams meet over North China,as do the anomalous southerlies and northerlies.However,the wind field features differ among the different levels of continuous autumn rain:with an increase in the level of continuous rain,the wind speed converging over North China increases. (5)In the sea level pressure field,the blocking high between Lake Balkhash and Lake Baikal strengthens,and North China is located in the peripheral region of the blocking high.Positive sea level pressure anomalies are located over North China.However,among the different levels of continuous autumn rain,the blocking high strength shows some differences,as does the extent of the enhancement of the blocking high,which is maximum for the 11 d and above level,followed by the 5-7 d level,and is minimum for the 8-10 d level.
Continuous autumn rain is long in duration,meaning it can easily cause crop mold and other adverse effects relating to daily life and industrial and agricultural production.In order to mitigate such losses caused by continuous autumn rain,it is important to study in depth the climate characteristics of continuous autumn rain and its causes.The present study does this based on the daily rainfall and sunshine data of 753 meteorological stations in China in autumn (September-November) from 1961 to 2010,along with NCEP/NCAR reanalysis data for the period 1948-2010.After defining continuous autumn rain in China,its climate characteristics for different levels (5-7 d,8-10 d,and 11 d and above) are analyzed.Based on a general survey of regions where continuous autumn rain was found to happen often during 1961-2010,China is divided into four regions of continuous autumn rain;namely,North China,Southwest China,the Changjiang-Huaihe basin,and South China,where representative stations are Xingtai (Hebei Province),Wufeng (Hubei Province),Gushi (Henan Province) and Yongan (Fujian Province),respectively.The circulation characteristics of continuous autumn rain and continuous autumn rain of different levels in North China are also analyzed.The results show that: (1)The accumulated frequency of continuous autumn rain and continuous autumn rain of different levels mainly concentrates in the mid-upper reaches of the Yangtze River during 1961-2010,and is very small in the areas north to the Yellow River.With an increase in the level of rain,the high-frequency areas move from southeast to southwest.The frequency standard deviation is similar to the frequency of continuous autumn rain and continuous autumn rain of different levels. (2)During the continuous autumn rain and continuous autumn rain of different levels in North China,in the 500 hPa geopotential height field,the northern cold air is guided to the south by northerly flow after the East Asian trough,and southern warm air is guided to the north by southerly flow on the west side of the subtropical high.The cold and warm air masses meet over North China,which is beneficial to the formation of the continuous rain weather.Positive height anomalies are located over North China,but negative height anomalies are located in the east and west sides of North China. (3)The circulation patterns feature a number of differences among the different levels of continuous autumn rain.The East Asian trough and Urals ridge are the strongest and located farthest east for the 8-10 d level,followed by the 11 d and above level,and finally the 5-7 d level.The trough is most obvious over Lake Balkhash for the 8-10 d level. (4)In the 850-hPa wind field,the enhanced southern and northern air streams meet over North China,as do the anomalous southerlies and northerlies.However,the wind field features differ among the different levels of continuous autumn rain:with an increase in the level of continuous rain,the wind speed converging over North China increases. (5)In the sea level pressure field,the blocking high between Lake Balkhash and Lake Baikal strengthens,and North China is located in the peripheral region of the blocking high.Positive sea level pressure anomalies are located over North China.However,among the different levels of continuous autumn rain,the blocking high strength shows some differences,as does the extent of the enhancement of the blocking high,which is maximum for the 11 d and above level,followed by the 5-7 d level,and is minimum for the 8-10 d level.
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