ISSN 1000-0526
CN 11-2282/P
CN 11-2282/P
Volume 44,Issue 11,2018 Table of Contents
2018, 44(11):1377-1390.
DOI: 10.7519/j.issn.1000-0526.2018.11.001
Abstract:
With the progress of Chinamade large aircraft and natural icing flight test in recent years, aircraft icing which is dangerous for flight safety, catches more and more attentions from both aviation and meteorology sectors now. Based on atmospheric temperature and humidity stratification profile, an improved icing potential algorithm with high probability of detection (POD), low false alarms ratio (FAR), easy application and practicability, is introduced in this article. The algorithm is verified and evaluated against 26 flight test/pilot reports. It is found that the diagnosed icing potential has high accordance with aircraft observation, and can give the approximate icing height and area in multiple weather conditions. By combing surface observation, radiosonde and satellite data, the algorithm is also verified in an aircraft natural icing observation experiment in Anqing, and the result shows that the algorithm can diagnose the particular height of icing level as well as the production and consumption of supercooled water, which has high consistency with aircraft sounding.
With the progress of Chinamade large aircraft and natural icing flight test in recent years, aircraft icing which is dangerous for flight safety, catches more and more attentions from both aviation and meteorology sectors now. Based on atmospheric temperature and humidity stratification profile, an improved icing potential algorithm with high probability of detection (POD), low false alarms ratio (FAR), easy application and practicability, is introduced in this article. The algorithm is verified and evaluated against 26 flight test/pilot reports. It is found that the diagnosed icing potential has high accordance with aircraft observation, and can give the approximate icing height and area in multiple weather conditions. By combing surface observation, radiosonde and satellite data, the algorithm is also verified in an aircraft natural icing observation experiment in Anqing, and the result shows that the algorithm can diagnose the particular height of icing level as well as the production and consumption of supercooled water, which has high consistency with aircraft sounding.
2018, 44(11):1391-1403.
DOI: 10.7519/j.issn.1000-0526.2018.11.002
Abstract:
Based on conventional meteorological observational data, NCEP/NCAR 1°×1° 6 h reanalysis data, the blackbody temperature of FY2E satellite infrared images, Cband Doppler radar sounding data and simulation results with mesoscale numerical model, a locally heavy rainstorm that occurred in the evening of 24 May 2012 is studied. For the mesoscale convective systems, the evolution characteristics and their formation mechanisms are analyzed in detail. The results show that the best configuration of upper and low layer systems made the generation of heavy rainstorm. As the peak of precipitation appeared, the lower layer became warmer and wetter, significantly convectionalunstable stratification from surface to 500 hPa appeared, and vertical wind shear reached 14 m·s-1 in 700-500 hPa. In zonal structure, easterly enhanced at lower layer in the rainstorm center, zonal wind convergenced under 300 hPa, and its center intensity was -28×10-5 s-1, center intensity of updraft under 150 hPa was 21 m·s-1, convergence of moisture flux near surface was -20×10-5 g·hPa-1·s-1·cm-2. In meridional direction, southerly speed convergenced under 500 hPa in the rainstorm center, then updraft enhanced. Meridional strength was the same as those in zonal direction. Convergence intensity of moisture flux at lower layer was -30×10-5 g·hPa-1·s-1·cm-2, 〖JP2〗stronger than that of zonal intensity. In addition, 〖JP〗topographic forcing affected south wind significantly, and the lifting speed was 0.4-1.0 m·s-1. Moreover, heavy rainfalls were different in the four stages, namely, initial, enhancement, fallback and attenuation. While cold air in surface layer over Kunming enhanced, convective cell on its east side moved to Kunming, then heavy rainfall generated. Thereafter, southerly wind pulsated, local wet layer was thickened, vertical wind shear increased, convective cell enhanced twice, and precipitation peak appeared. The formation of the third precipitation peak was mainly caused by southerly wind pulsating and convective cell complicating, but because volume of incorporation cell was smaller than that of local cell, precipitation peak created by the local cell was obvious smaller than the peaks in the previous ones. Convective precipitation echo belonged to warm cloud property and had tropics low centroid characteristic.
Based on conventional meteorological observational data, NCEP/NCAR 1°×1° 6 h reanalysis data, the blackbody temperature of FY2E satellite infrared images, Cband Doppler radar sounding data and simulation results with mesoscale numerical model, a locally heavy rainstorm that occurred in the evening of 24 May 2012 is studied. For the mesoscale convective systems, the evolution characteristics and their formation mechanisms are analyzed in detail. The results show that the best configuration of upper and low layer systems made the generation of heavy rainstorm. As the peak of precipitation appeared, the lower layer became warmer and wetter, significantly convectionalunstable stratification from surface to 500 hPa appeared, and vertical wind shear reached 14 m·s-1 in 700-500 hPa. In zonal structure, easterly enhanced at lower layer in the rainstorm center, zonal wind convergenced under 300 hPa, and its center intensity was -28×10-5 s-1, center intensity of updraft under 150 hPa was 21 m·s-1, convergence of moisture flux near surface was -20×10-5 g·hPa-1·s-1·cm-2. In meridional direction, southerly speed convergenced under 500 hPa in the rainstorm center, then updraft enhanced. Meridional strength was the same as those in zonal direction. Convergence intensity of moisture flux at lower layer was -30×10-5 g·hPa-1·s-1·cm-2, 〖JP2〗stronger than that of zonal intensity. In addition, 〖JP〗topographic forcing affected south wind significantly, and the lifting speed was 0.4-1.0 m·s-1. Moreover, heavy rainfalls were different in the four stages, namely, initial, enhancement, fallback and attenuation. While cold air in surface layer over Kunming enhanced, convective cell on its east side moved to Kunming, then heavy rainfall generated. Thereafter, southerly wind pulsated, local wet layer was thickened, vertical wind shear increased, convective cell enhanced twice, and precipitation peak appeared. The formation of the third precipitation peak was mainly caused by southerly wind pulsating and convective cell complicating, but because volume of incorporation cell was smaller than that of local cell, precipitation peak created by the local cell was obvious smaller than the peaks in the previous ones. Convective precipitation echo belonged to warm cloud property and had tropics low centroid characteristic.
2018, 44(11):1404-1413.
DOI: 10.7519/j.issn.1000-0526.2018.11.003
Abstract:
Based on conventional observation data, Xi’an and Ankang Doppler weather radar observation data and ECMWF numerical model data (0.25°×0.25°), an elevated thunderstorm process in Shaanxi in early winter of 2016 is analyzed. The results show that the thunderstorm area in the center and south of Shaanxi Province was located in the area of 350-500 km after surface cold front. Deep cold air cushion existed under 3 km in thunderstorm area. At the same time, there was temperature inversion in middlelow level and absolute stability of atmospheric stratification in low level. All these make clear that the thunderstorm was an elevated one. Through analyzing moist potential vorticity, saturated pseudoequivalent potential temperature, pseudoequivalent potential temperature and absolute vorticity, we found that the unstable mechanism is different in different regions.Unstable mechanism for Xi’an Region is conditional symmetric instability while unstable mechanism for Ankang Region is conditional instability. In conditional symmetric instability area there are a number of parallel snowfall echoes, parallel with vertical wind shear vector from 0 to 6 km. In conditional instability area there are small scale echoes. The strong vertical wind shear indicates that the atmospheric baroclinic is strong. Warm moist air flows between middlehigh layers enhance atmospheric baroclinicity, thus producing conditional symmetric instability which results in slantwise updraft. Southerly airflow in the lowmiddle level convey warm advections and water vapor which makes the atmosphere moister and warmer, making the atmosphere moister and warmer, but highlevel temperature advection is weak and the atmosphere is relativerly dry. So potential instability is formed. When the front surface uplift warm moist air makes it saturated, potential instability changes into conditional instability, resulting in vertical convection. Thus, there is a good correspondence between the instability and the ascending motion and the echo height.
Based on conventional observation data, Xi’an and Ankang Doppler weather radar observation data and ECMWF numerical model data (0.25°×0.25°), an elevated thunderstorm process in Shaanxi in early winter of 2016 is analyzed. The results show that the thunderstorm area in the center and south of Shaanxi Province was located in the area of 350-500 km after surface cold front. Deep cold air cushion existed under 3 km in thunderstorm area. At the same time, there was temperature inversion in middlelow level and absolute stability of atmospheric stratification in low level. All these make clear that the thunderstorm was an elevated one. Through analyzing moist potential vorticity, saturated pseudoequivalent potential temperature, pseudoequivalent potential temperature and absolute vorticity, we found that the unstable mechanism is different in different regions.Unstable mechanism for Xi’an Region is conditional symmetric instability while unstable mechanism for Ankang Region is conditional instability. In conditional symmetric instability area there are a number of parallel snowfall echoes, parallel with vertical wind shear vector from 0 to 6 km. In conditional instability area there are small scale echoes. The strong vertical wind shear indicates that the atmospheric baroclinic is strong. Warm moist air flows between middlehigh layers enhance atmospheric baroclinicity, thus producing conditional symmetric instability which results in slantwise updraft. Southerly airflow in the lowmiddle level convey warm advections and water vapor which makes the atmosphere moister and warmer, making the atmosphere moister and warmer, but highlevel temperature advection is weak and the atmosphere is relativerly dry. So potential instability is formed. When the front surface uplift warm moist air makes it saturated, potential instability changes into conditional instability, resulting in vertical convection. Thus, there is a good correspondence between the instability and the ascending motion and the echo height.
2018, 44(11):1414-1423.
DOI: 10.7519/j.issn.1000-0526.2018.11.004
Abstract:
Using conventional weather data, FY-2E satellite data, Doppler radar products, lightning location data, automatic weather station data, this paper analyzes the 4 April 2015 eveningtonight thunderstorm gale process in Sichuan Basin. Our analysis shows that the thunderstorm gale process was formed by the cold front forced uplift on warm air mass as well as dry and cold air into the warm area. The area of hollow dry layer, large temperature lapse rate, coupling of highlow jet area and the lowlevel temperature near the ridge were conducive to the potential area of extreme thunderstorm gale. This area provided a favorable environmental condition for the thunderstorm such as significant unstable conditions, water vapor, dynamic uplift, etc. Cold air firstly invaded from the middle and lower layers of the northwestern part of the basin and triggered a series of thunderstorm cells on the lowlevel shear line, which developed rapidly in the most favorable area for the development of convection. The interaction of the mesoscale vortex, the front inflow and the posterior inflow into the northern part of the latent region led to the formation of a single bow echo, which had much higher reflectivity and liquid water content than ordinary thunderstorm. According to the development characteristics of radar echo, the extreme gale was caused by the wet downburst brought by single bow ech. The descending height of the high reflectivity factor in the bow echo means that the sinking air stream was accompanied by a drop in precipitation particles. The dry air was trapped in the sinking air stream and raindrops evaporated quickly, greatly increasing the intensity of the sinking air stream, and thus increasing the strength of the gale. Our analysis also indicates that, by analyzing the background conditions of convective development, forecasters could identify the potential regions for the most favorable convective development paying close attention to the location of the trigger conditions and the characteristics of the radar echo shape as well as the evolution characteristics in the region could be helpful for the early warning of gale weather.
Using conventional weather data, FY-2E satellite data, Doppler radar products, lightning location data, automatic weather station data, this paper analyzes the 4 April 2015 eveningtonight thunderstorm gale process in Sichuan Basin. Our analysis shows that the thunderstorm gale process was formed by the cold front forced uplift on warm air mass as well as dry and cold air into the warm area. The area of hollow dry layer, large temperature lapse rate, coupling of highlow jet area and the lowlevel temperature near the ridge were conducive to the potential area of extreme thunderstorm gale. This area provided a favorable environmental condition for the thunderstorm such as significant unstable conditions, water vapor, dynamic uplift, etc. Cold air firstly invaded from the middle and lower layers of the northwestern part of the basin and triggered a series of thunderstorm cells on the lowlevel shear line, which developed rapidly in the most favorable area for the development of convection. The interaction of the mesoscale vortex, the front inflow and the posterior inflow into the northern part of the latent region led to the formation of a single bow echo, which had much higher reflectivity and liquid water content than ordinary thunderstorm. According to the development characteristics of radar echo, the extreme gale was caused by the wet downburst brought by single bow ech. The descending height of the high reflectivity factor in the bow echo means that the sinking air stream was accompanied by a drop in precipitation particles. The dry air was trapped in the sinking air stream and raindrops evaporated quickly, greatly increasing the intensity of the sinking air stream, and thus increasing the strength of the gale. Our analysis also indicates that, by analyzing the background conditions of convective development, forecasters could identify the potential regions for the most favorable convective development paying close attention to the location of the trigger conditions and the characteristics of the radar echo shape as well as the evolution characteristics in the region could be helpful for the early warning of gale weather.
ZHANG Pingping
,
SUN Jun
,
CHE Qin
,
DONG Liangpeng
,
ZHONG Min
,
CHEN Xuan
,
ZHANG Mengmeng
,
ZHANG Ning
2018, 44(11):1424-1433.
DOI: 10.7519/j.issn.1000-0526.2018.11.005
Abstract:
Based on NCEP/NCAR reanalysis data and other conventional observation data, the abnormal characteristics of meteorological factors during an extremely heavy rainfall process in 2016 were analyzed. The results showed that the extremely heavy rainfall was a direct result of atmospheric circulation anomalies. The 500 hPa subtropical high was stronger than the climatic mean, which was conducive to the strengthening of water vapor transport, leading to stronger southerly normalized anomaly. The 850 hPa strong vortex development and 200 hPa shunting area formation contributed to the vertical uplift anomaly. By further analyzing the abnormal meteorological factors over the extremely rainfall sites, we found the absolute values of precipitable water, K index and 850 hPa divergence were higher than the climatic mean values for 1.5σ, and also higher than upper quartile of historical data. Finally, synoptic conceptual model and quantitative configuration diagram of abnormal meteorological factors were built based on above researches.
Based on NCEP/NCAR reanalysis data and other conventional observation data, the abnormal characteristics of meteorological factors during an extremely heavy rainfall process in 2016 were analyzed. The results showed that the extremely heavy rainfall was a direct result of atmospheric circulation anomalies. The 500 hPa subtropical high was stronger than the climatic mean, which was conducive to the strengthening of water vapor transport, leading to stronger southerly normalized anomaly. The 850 hPa strong vortex development and 200 hPa shunting area formation contributed to the vertical uplift anomaly. By further analyzing the abnormal meteorological factors over the extremely rainfall sites, we found the absolute values of precipitable water, K index and 850 hPa divergence were higher than the climatic mean values for 1.5σ, and also higher than upper quartile of historical data. Finally, synoptic conceptual model and quantitative configuration diagram of abnormal meteorological factors were built based on above researches.
2018, 44(11):1434-1444.
DOI: 10.7519/j.issn.1000-0526.2018.11.006
Abstract:
Generally, radar beam blockage caused by terrain remains unchanged for long. Research on the situation of radar terrain blockage is helpful for improving effectiveness and reliability of radar data. By using Advanced Spaceborne Thermal Emission and reflection Radiometer Global Digital Elevation Model (ASTER GDEM) terrain data, the terrain blockage of 208 existing Chinese next generation radar sites is computed. Beam blockage coefficient in a 200 km radius around radar sites is calculated at 9 observation elevation angles of Volume Coverage Pattern (VCP) modes 21. Maps of effective observation region where radar beam is not blocked are drawn while the elevation angle of radar remains at 0.5°, 1.45°, 2.4° and 3.35° respectively. The effectively covered area of radar sites is obtained according to these maps. Calculation result shows that the average blockage ratios of Chinese next generation radars within 200 km at 4 different elevation angles (0.5°, 1.45°, 2.4° and 3.35°) are 30.7%, 8.5%, 2.5% and 1.0% respectively, and the average effectively covered areas are 83210.5, 109354.2, 118170.9 and 121631.5 km2 accordingly. Most of Chinese next generation radar sites can cover the surrounding area effectively as the influence of terrain blockage remains very low except a few sites near mountains.
Generally, radar beam blockage caused by terrain remains unchanged for long. Research on the situation of radar terrain blockage is helpful for improving effectiveness and reliability of radar data. By using Advanced Spaceborne Thermal Emission and reflection Radiometer Global Digital Elevation Model (ASTER GDEM) terrain data, the terrain blockage of 208 existing Chinese next generation radar sites is computed. Beam blockage coefficient in a 200 km radius around radar sites is calculated at 9 observation elevation angles of Volume Coverage Pattern (VCP) modes 21. Maps of effective observation region where radar beam is not blocked are drawn while the elevation angle of radar remains at 0.5°, 1.45°, 2.4° and 3.35° respectively. The effectively covered area of radar sites is obtained according to these maps. Calculation result shows that the average blockage ratios of Chinese next generation radars within 200 km at 4 different elevation angles (0.5°, 1.45°, 2.4° and 3.35°) are 30.7%, 8.5%, 2.5% and 1.0% respectively, and the average effectively covered areas are 83210.5, 109354.2, 118170.9 and 121631.5 km2 accordingly. Most of Chinese next generation radar sites can cover the surrounding area effectively as the influence of terrain blockage remains very low except a few sites near mountains.
2018, 44(11):1445-1453.
DOI: 10.7519/j.issn.1000-0526.2018.11.007
Abstract:
Based on the observation data and FY2 satellite cloud image, statistical analysis is carried out on the configuration of weather situation and the evolution of satellite cloud images of 76 shorttime heavy rainfall processes in Gansu Province during May and September of 2010-2015. The results show that there are six kinds of characteristic cloud types, which are related to the shortterm heavy rainfall in Gansu Province, including subtropical high edge, comma cloud, front of the cold front, overlay of cold front tail and South Asia high, the back of the cold vortex, elliptic cloud front of the weak cold front. The subtropical high edge, front of the cold front and elliptic cloud front of the weak cold front types, are related to the low level warm advection forcing. The comma cloud and the overlay of cold front tail and east of South Asia types, are mainly affected by strong convergence of warm and cold advections of high and low levels. The back of the cold vortex type is formed by high altitude cold advection. The overlay of cold front tail and east of South Asia type has better predictive indication.
Based on the observation data and FY2 satellite cloud image, statistical analysis is carried out on the configuration of weather situation and the evolution of satellite cloud images of 76 shorttime heavy rainfall processes in Gansu Province during May and September of 2010-2015. The results show that there are six kinds of characteristic cloud types, which are related to the shortterm heavy rainfall in Gansu Province, including subtropical high edge, comma cloud, front of the cold front, overlay of cold front tail and South Asia high, the back of the cold vortex, elliptic cloud front of the weak cold front. The subtropical high edge, front of the cold front and elliptic cloud front of the weak cold front types, are related to the low level warm advection forcing. The comma cloud and the overlay of cold front tail and east of South Asia types, are mainly affected by strong convergence of warm and cold advections of high and low levels. The back of the cold vortex type is formed by high altitude cold advection. The overlay of cold front tail and east of South Asia type has better predictive indication.
2018, 44(11):1454-1463.
DOI: 10.7519/j.issn.1000-0526.2018.11.008
Abstract:
Based on the PM2.5 air quality monitoring data of Hubei Province in winter months during 2015-2016, the PM2.5 mass concentration is classified by EOF method and its synoptic patterns are analyzed. The correlation between PM2.5 and largescale circulation is discussed and correlation index with SLP is established. The results show that the PM2.5 mass concentration in central part of Hubei is higher than in the easten and westen parts. There are large fluctuations in the PM2.5 time series and a downward trend in the recent two years. Four distinguished modes of PM2.5 are clarified, which can explain over 86.2% of the variance. The synoptic patterns are transmission type and local accumulated type. The PM2.5 mass concentration of transmission type is higher than the other one. The transmission type presents pollution in the whole region, pollution in the west and pollution in the northcentral, respectively. Northerly airflow dominates Hubei during the whole region pollution, bringing PM2.5 from northern China. For the west region pollution of transmission type, the pollutions and moisture are carried to western Hubei by east winds and the western Hubei mountain makes the pollutions accumulate in this area. The northcentral region pollution shows a collection effect of northeast and northwest wind. The local accumulated type pollution in eastern Hubei and southcentral Hubei are under the common cause of static weather condition and terrain. The transporting paths of three transmission type pollution are the north path, east path and northeast path.With the decrease of highlevel East Asia trough and lowlevel cold continental high pressure, PM2.5 mass concentration increases. The correlation index with the sea level pressure is closely related to the PM2.5 mass concentration and the first EOF mode time coefficient which has certain significance for pollution forecasting.
Based on the PM2.5 air quality monitoring data of Hubei Province in winter months during 2015-2016, the PM2.5 mass concentration is classified by EOF method and its synoptic patterns are analyzed. The correlation between PM2.5 and largescale circulation is discussed and correlation index with SLP is established. The results show that the PM2.5 mass concentration in central part of Hubei is higher than in the easten and westen parts. There are large fluctuations in the PM2.5 time series and a downward trend in the recent two years. Four distinguished modes of PM2.5 are clarified, which can explain over 86.2% of the variance. The synoptic patterns are transmission type and local accumulated type. The PM2.5 mass concentration of transmission type is higher than the other one. The transmission type presents pollution in the whole region, pollution in the west and pollution in the northcentral, respectively. Northerly airflow dominates Hubei during the whole region pollution, bringing PM2.5 from northern China. For the west region pollution of transmission type, the pollutions and moisture are carried to western Hubei by east winds and the western Hubei mountain makes the pollutions accumulate in this area. The northcentral region pollution shows a collection effect of northeast and northwest wind. The local accumulated type pollution in eastern Hubei and southcentral Hubei are under the common cause of static weather condition and terrain. The transporting paths of three transmission type pollution are the north path, east path and northeast path.With the decrease of highlevel East Asia trough and lowlevel cold continental high pressure, PM2.5 mass concentration increases. The correlation index with the sea level pressure is closely related to the PM2.5 mass concentration and the first EOF mode time coefficient which has certain significance for pollution forecasting.
2018, 44(11):1464-1470.
DOI: 10.7519/j.issn.1000-0526.2018.11.009
Abstract:
Skillful precipitation prediction is useful in managing water resources and preventing droughts and floods for the Huaihe River Basin. A hybrid spatiotemporal statistical downscaling model based on the ensemble reforecast dataset (1991-2014) of the seasonal climate model (CSM1.1m) was developed to predict the summer monthly precipitation over the basin ahead of 1-3 months, i.e., starting from March, April and May. Crossvalidation tests indicate that compared with CSM1.1m, the established statistical downscaling model is more skillful for the precipitation forecasted in March, April and May for four ensemble schemes. Independent sample tests present that the statistical downscaling model can reduce prediction error, especially for precipitation in June and August forecasted in March and May. These results suggest that it is possible to use the statistical downscaling method for precipitation probability forecasting and further hydrological forecasting in summer over Huaihe River Basin.
Skillful precipitation prediction is useful in managing water resources and preventing droughts and floods for the Huaihe River Basin. A hybrid spatiotemporal statistical downscaling model based on the ensemble reforecast dataset (1991-2014) of the seasonal climate model (CSM1.1m) was developed to predict the summer monthly precipitation over the basin ahead of 1-3 months, i.e., starting from March, April and May. Crossvalidation tests indicate that compared with CSM1.1m, the established statistical downscaling model is more skillful for the precipitation forecasted in March, April and May for four ensemble schemes. Independent sample tests present that the statistical downscaling model can reduce prediction error, especially for precipitation in June and August forecasted in March and May. These results suggest that it is possible to use the statistical downscaling method for precipitation probability forecasting and further hydrological forecasting in summer over Huaihe River Basin.
2018, 44(11):1471-1478.
DOI: 10.7519/j.issn.1000-0526.2018.11.010
Abstract:
Based on the daily observations of Beijings 20 conventional meteorological stations from 1976 to 2015 and the urban development data of Beijing in the same period, the distribution and variation characteristics of relative humidity in Beijing and its response to urbanization are analyzed by using a new classification method of representative stations in urban and suburban areas. The results show that the spatial distribution of relative humidity in Beijing is uneven, in which the spatial distribution of relative humidity is mainly affected by topography in the early stage of urbanization and by urbanization in the stage of higher urbanization. In recent 40 years, the average relative humidity in Beijing presents a downward trend with a linear tendency rate of -0.9%·10 a-1, and the decline rate of urban relative humidity is larger than that of suburbs especially after 1990s. Moreover, the intensity of urban dry islands in Beijing shows an upward trend in the past 40 years, with a linear tendency rate of 1.3%·10 a-1. The urban dry island effect is the strongest in winter, followed by autumn and spring, and weaker in summer. Note that the dry island effect of Beijing has shown a more obvious trend of enhancement since 1995. Additionally, the urban dry island effect of Beijing is closely related to the urbanization process, and has a significant high correlation with the urbanization rate and the intensity of urban heat island, with the correlation coefficients as high as 0.87 and 0.86 respectively.
Based on the daily observations of Beijings 20 conventional meteorological stations from 1976 to 2015 and the urban development data of Beijing in the same period, the distribution and variation characteristics of relative humidity in Beijing and its response to urbanization are analyzed by using a new classification method of representative stations in urban and suburban areas. The results show that the spatial distribution of relative humidity in Beijing is uneven, in which the spatial distribution of relative humidity is mainly affected by topography in the early stage of urbanization and by urbanization in the stage of higher urbanization. In recent 40 years, the average relative humidity in Beijing presents a downward trend with a linear tendency rate of -0.9%·10 a-1, and the decline rate of urban relative humidity is larger than that of suburbs especially after 1990s. Moreover, the intensity of urban dry islands in Beijing shows an upward trend in the past 40 years, with a linear tendency rate of 1.3%·10 a-1. The urban dry island effect is the strongest in winter, followed by autumn and spring, and weaker in summer. Note that the dry island effect of Beijing has shown a more obvious trend of enhancement since 1995. Additionally, the urban dry island effect of Beijing is closely related to the urbanization process, and has a significant high correlation with the urbanization rate and the intensity of urban heat island, with the correlation coefficients as high as 0.87 and 0.86 respectively.
2018, 44(11):1479-1488.
DOI: 10.7519/j.issn.1000-0526.2018.11.011
Abstract:
The refined quantitative evaluation of precipitation process intensity is one of the important requirements in the modernization of meteorological operational services and a key link in the rainstorm disaster impact assessment research. By using rainfall observation data from 2410 weather stations since 1961 and precipitation background at stations to represent the regional characteristics, the beginning and end conditions of a single station and regional precipitation process are defined, and three evaluation indexes of precipitation process are extracted, including rainfall intensity, duration and range. In addition, three evaluation indexes in the process of precipitation are calculated based on the spatiotemporal precipitation data. Then, based on percentile distribution and probability statistics, the three evaluation indexes of precipitation process are subdivided and the comprehensive intensity evaluation model of precipitation process is established. Finally, the intensities of precipitation process are divided into five grades including extreme, extrasevere, severe, heavy, medium grades. The results of validating the evaluation method show that single station and regional precipitation intensity grade evaluation method is reasonable. It can not only reflect geographical features, but also characterize the effect of the precipitation process. This method has strong the maneuverability, and can be directly applied to meteorological service operations and heavy rain impact assessment. It can also be used for the storage of historic precipitation process case, providing basis for the characteristics analysis of disaster information.
The refined quantitative evaluation of precipitation process intensity is one of the important requirements in the modernization of meteorological operational services and a key link in the rainstorm disaster impact assessment research. By using rainfall observation data from 2410 weather stations since 1961 and precipitation background at stations to represent the regional characteristics, the beginning and end conditions of a single station and regional precipitation process are defined, and three evaluation indexes of precipitation process are extracted, including rainfall intensity, duration and range. In addition, three evaluation indexes in the process of precipitation are calculated based on the spatiotemporal precipitation data. Then, based on percentile distribution and probability statistics, the three evaluation indexes of precipitation process are subdivided and the comprehensive intensity evaluation model of precipitation process is established. Finally, the intensities of precipitation process are divided into five grades including extreme, extrasevere, severe, heavy, medium grades. The results of validating the evaluation method show that single station and regional precipitation intensity grade evaluation method is reasonable. It can not only reflect geographical features, but also characterize the effect of the precipitation process. This method has strong the maneuverability, and can be directly applied to meteorological service operations and heavy rain impact assessment. It can also be used for the storage of historic precipitation process case, providing basis for the characteristics analysis of disaster information.
2018, 44(11):1489-1500.
DOI: 10.7519/j.issn.1000-0526.2018.11.012
Abstract:
Using the PM2.5 mass concentration and surface wind data from February 2013 to January 2016 at Chaoyang Environmental Meteorological Station in Beijing, the characteristics of PM2.5 and its influence by surface wind are analyzed. The results show that the annual concentration of PM2.5 is 80.6±4.0 μg·m-3, 2.3 times the annual concentration limits (35 μg·m-3) regulated in the ambient air quality standard (GB3095-2012) of China. Its seasonal variation is obvious with the highest concentration in winter (115.1 μg·m-3) and the lowest in summer (58.5 μg·m-3). The dominant wind direction at Chaoyang Site in Beijing is ENE-E-ESE, and the wind speed ranges between 0.2-2.0 m·s-1. The concentration is the highest (109.1 μg·m-3) in the dominant ENE-E-ESE wind direction and the lowest (39.5 μg·m-3) in WNW-NW-NNW. With the increase of wind speed, PM2.5 concentration increases first and then decreases. The highest concentration (139.2 μg·m-3) appears at the wind speed of 0.4 m·s-1. When the wind speed is in 0.2-2.0 m·s-1, the concentration is mainly affected by ENE-E-ESE, and when the wind speed is 2-6 m·s-1, the value is influenced by ESE more. By comparing with the PM2.5 data from other sites, we found that the different characteristics of pollution sources and ground winds result in the difference of PM2.5 mass concentration in different wind directions.
Using the PM2.5 mass concentration and surface wind data from February 2013 to January 2016 at Chaoyang Environmental Meteorological Station in Beijing, the characteristics of PM2.5 and its influence by surface wind are analyzed. The results show that the annual concentration of PM2.5 is 80.6±4.0 μg·m-3, 2.3 times the annual concentration limits (35 μg·m-3) regulated in the ambient air quality standard (GB3095-2012) of China. Its seasonal variation is obvious with the highest concentration in winter (115.1 μg·m-3) and the lowest in summer (58.5 μg·m-3). The dominant wind direction at Chaoyang Site in Beijing is ENE-E-ESE, and the wind speed ranges between 0.2-2.0 m·s-1. The concentration is the highest (109.1 μg·m-3) in the dominant ENE-E-ESE wind direction and the lowest (39.5 μg·m-3) in WNW-NW-NNW. With the increase of wind speed, PM2.5 concentration increases first and then decreases. The highest concentration (139.2 μg·m-3) appears at the wind speed of 0.4 m·s-1. When the wind speed is in 0.2-2.0 m·s-1, the concentration is mainly affected by ENE-E-ESE, and when the wind speed is 2-6 m·s-1, the value is influenced by ESE more. By comparing with the PM2.5 data from other sites, we found that the different characteristics of pollution sources and ground winds result in the difference of PM2.5 mass concentration in different wind directions.
2018, 44(11):1501-1508.
DOI: 10.7519/j.issn.1000-0526.2018.11.013
Abstract:
The main characteristics of the general atmospheric circulation in August 2018 were as follows. There was one polar vortex center in the Northern Hemisphere and stronger than usual. The circulation in Eurasian middlehigh latitudes showed a multiwave pattern. The strength of western North Pacific subtropical high was much stronger and the location was west compared to normal years. The monthly mean temperature was 21.9℃, 1.1℃ higher than normal, which ranks the fourth highest since 1961. The monthly mean precipitation amount was 127.7 mm, which was more than normal (105.3 mm) by 21.3%, and the precipitation in central China was less than usual. Eleven rainfall processes with some extreme records occurred in China this month. Ten tropical cyclones were active over the western North Pacific and the South China Sea. Among them, Typhoons Jongdari (1812), Yagi (1814), Bebinca (1816) and Rumbia (1812) made landfall in China. The total and landing numbers of tropical cyclones were more than usual. Longlasting high temperature events happened in central and eastern China. Meanwhile, convection events occurred frequently with a wide range of influencing areas.
The main characteristics of the general atmospheric circulation in August 2018 were as follows. There was one polar vortex center in the Northern Hemisphere and stronger than usual. The circulation in Eurasian middlehigh latitudes showed a multiwave pattern. The strength of western North Pacific subtropical high was much stronger and the location was west compared to normal years. The monthly mean temperature was 21.9℃, 1.1℃ higher than normal, which ranks the fourth highest since 1961. The monthly mean precipitation amount was 127.7 mm, which was more than normal (105.3 mm) by 21.3%, and the precipitation in central China was less than usual. Eleven rainfall processes with some extreme records occurred in China this month. Ten tropical cyclones were active over the western North Pacific and the South China Sea. Among them, Typhoons Jongdari (1812), Yagi (1814), Bebinca (1816) and Rumbia (1812) made landfall in China. The total and landing numbers of tropical cyclones were more than usual. Longlasting high temperature events happened in central and eastern China. Meanwhile, convection events occurred frequently with a wide range of influencing areas.
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ISSN:1000-0526 CN:11-2282/P