采用WRF(Weather Research and Forecasting)模式4种边界层参数化方案对青藏高原那曲地区边界层特征进行了数值模拟,并利用"第三次青藏高原大气科学试验"在青藏高原那曲地区5个站点的观测资料对模拟结果进行验证,分析不同参...采用WRF(Weather Research and Forecasting)模式4种边界层参数化方案对青藏高原那曲地区边界层特征进行了数值模拟,并利用"第三次青藏高原大气科学试验"在青藏高原那曲地区5个站点的观测资料对模拟结果进行验证,分析不同参数化方案在那曲地区的适用性。研究表明,YSU、MYJ、ACM2和BouLac方案对2 m气温和地表温度的模拟偏低。BouLac方案模拟的地表温度偏差较小。通过对能量平衡各分量的对比分析发现,温度模拟偏低可能是向下长波辐射模拟偏低以及感热通量和潜热通量交换过强导致的。对于边界层风、位温和相对湿度垂直结构的模拟,局地方案的模拟效果均优于非局地方案。BouLac方案对那曲地区近地层温度、边界层内位温和相对湿度的垂直分布模拟效果较好。展开更多
中国中东部地区的空气污染主要集中在京津冀、长三角、珠三角、东北地区及汾渭平原等区域,各区域的污染排放特征各异.本文应用基于CMAQ(The Community Multiscale Air Quality)模式的自适应“nudging”源反演方法,反演中国中东部地区201...中国中东部地区的空气污染主要集中在京津冀、长三角、珠三角、东北地区及汾渭平原等区域,各区域的污染排放特征各异.本文应用基于CMAQ(The Community Multiscale Air Quality)模式的自适应“nudging”源反演方法,反演中国中东部地区2016年12月—2017年1月逐日NOx污染源,分析上述主要污染区的污染物排放强度空间分布特征,并与2016年MEIC(The Multi-resolution emission inventory for China)排放源进行比较,检验反演源的可靠性.结果表明,2016年冬季各个区域反演源NOx排放强度空间分布特征与2016年MEIC排放源基本一致.京津冀地区高强度排放区域形成沿山前区域东北-西南走向的NOx高强度排放带;长三角地区NOx高强度排放区域位于常州、苏州、上海和湖州等城市构成的城市群;珠三角地区NOx高强度排放区域位于以广州为中心的大范围城市群且排放强度呈现向四周逐渐降低的放射状分布;东北地区NOx高强度排放区域空间分布特征呈现以城市为中心且稀疏分布;汾渭平原排放区域呈现以城市为中心且向峡谷中间集中分布,排放区域轮廓与汾渭平原狭长的新月状相符.展开更多
This paper aims at constructing an emission source inversion model using a variational processing method and adaptive nudging scheme for the Community Multiscale Air Quality Model (CMAQ) based on satellite data to inv...This paper aims at constructing an emission source inversion model using a variational processing method and adaptive nudging scheme for the Community Multiscale Air Quality Model (CMAQ) based on satellite data to investigate the applicability of high resolution OMI (Ozone Monitoring Instrument) column concentration data for air quality forecasts over the North China. The results show a reasonable consistency and good correlation between the spatial distributions of NO2 from surface and OMI satellite measurements in both winter and summer. Such OMI products may be used to implement integrated variational analysis based on observation data on the ground. With linear and variational corrections made, the spatial distribution of OMI NO2 clearly revealed more localized distributing characteristics of NO2 concentration. With such information, emission sources in the southwest and southeast of North China are found to have greater impacts on air quality in Beijing. When the retrieved emission source inventory based on high-resolution OMI NO2 data was used, the coupled Weather Research Forecasting CMAQ model (WRF-CMAQ) performed significantly better in forecasting NO2 concentration level and its tendency as reflected by the more consistencies between the NO2 concentrations from surface observation and model result. In conclusion, satellite data are particularly important for simulating NO2 concentrations on urban and street-block scale. High-resolution OMI NO2 data are applicable for inversing NOx emission source inventory, assessing the regional pollution status and pollution control strategy, and improving the model forecasting results on urban scale.展开更多
Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends...Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends on a decadal time scale: frequency of rainstorms increases significantly after the 1990 s, while summer precipitation in East China decreases during the same period. Analysis of the spatial distribution of summer rainstorm frequency from 1961 to 2010 indicates that it decreases from the southeast to the northwest at the east edge of the large-scale topography associated with the plateaus. Spatial distribution of rainstorms with daily rainfall greater than 50 mm is characterized by a "high in the southeast and low in the northwest" pattern, similar to the staircase distribution of the topography. However, the spatial distribution of variation in both summer precipitation and frequency of extreme rainstorms under global warming differs significantly from the three-step staircase topography. It is shown that moisture characteristics of summer precipitation and extreme rainstorms during the monsoon season in East China, including moisture transport pathways, moist flow pattern, and spatial structure of the merging area of moist flows, differ significantly. Areas of frequent rainstorms include the Yangtze River Valley and South China. Column-integrated moisture transport and its spatial structure could be summarized as a "merging" of three branches of intense moist flows from low and middle latitude oceans, and "convergence" of column-integrated moisture fluxes. The merging area for moist flow associated with rainstorms in the high frequency region is located slightly to the south of the monsoonal precipitation or non-rainstorm precipitation, with significantly strong moisture convergence. In addition, the summer moist flow pattern in East China has a great influence on the frequency of extreme rainstorms. Moisture flux vectors in the region of frequent rainstorms correspond to vortical flow pattern. A comparison of moisture flux vectors associated with non-rainstorms and rainstorms indicates that the moist vortex associated with rainstorms is smaller in size and located to the south of the precipitation maximum, while the moist vortex associated with non-rainstorms is larger and located to the north. It is shown that column-integrated moist transport vortices and the structure of moist flux convergence have significant impacts on the north-south oscillation of frequent rainstorm areas in East China, which is synchronized with the maximum vorticity of moisture transport and the minimum of convergence on the decadal time scale. Synthesis of moisture transport pathways and related circulation impacts leads to a conceptual model of moisture flow associated with rainstorms.展开更多
Tomé and Miranda’s climate trend turning discriminatory model is used to identify the spatial-temporal characteristics of the interdecadal turning of winter/summer climate modes at stations and in eight sub-area...Tomé and Miranda’s climate trend turning discriminatory model is used to identify the spatial-temporal characteristics of the interdecadal turning of winter/summer climate modes at stations and in eight sub-areas over Chinese mainland based on the 1961–2000 observations. It is found that the stations with close occurrence years of the interdecadal trend turning (ITT) and coincident trends after the ITT exhibit a zonal distribution. A view is accordingly proposed that the interdecadal turnings of climate modes in China have remarkably regional structures. The research results show that after the early 1980s, winter climate over Chinese mainland overall trends towards a “warm-wet” mode, while summer climate had an abrupt change into “warm wet” mode in the late 1980s, suggesting that the time of the “warm-wet” mode turning for winter climate is earlier than that for summer climate. The regional characteristics and test results of the ITTs in eight sub-areas suggest that winter climate exhibits a distinctive “warm-dry” trend in North China after the late 1970s, and a slight “warm-dry” trend in Northeast China, South China, and Southwest China after the late 1980s. A “warm-wet” trend appears in the rest four sub-areas (the middle and lower reaches of the Yangtze River and the Huaihe River Valley, briefly Jianghuai, the east of the Tibetan plateau, and the east and west of Northwest China) after the early 1980s. The summer climate trends towards a “warm-dry” mode in Northeast China, North China and the east of Northwest China after the late 1980s, but a “warm-wet” mode appears in Southwest China and the east of the Tibetan plateau after the middle 1970s, as well as in Jianghuai and the west of Northwest China after the early 1980s. Specially, summer climate in South China started a “cold-wet” trend in 1984.展开更多
This paper presents a comprehensive observa-tion technique on derived aerosols data from mobile sun-photometer graph and Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) observation. Research results sugges...This paper presents a comprehensive observa-tion technique on derived aerosols data from mobile sun-photometer graph and Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) observation. Research results suggest that after being treated by the variational technique with respect to sunphotometer observations, the Terra- MODIS remote sensing aerosol data are remarkably im-proved, thus for the first time revealing features of the influ-ence of aerosols and pollution emissions of Beijing and its adjoining areas (Hebei, Shandong, etc. provinces). The re-gional impact features of aerosols are related with the pe-ripheral U-shape topography of Beijing. Analyses with Hy-brid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT-4) and meteorological data in the case studied confirm the pollutants diffusion process along the trajectory from the sources in the south-west region, and the regional aerosol impact features.展开更多
The aerosol distribution in Beijing and peripheral cities agglomeration (BPCA) and its re- gional climatic effect are investigated on the basis of the statistical analyses of satellite Total Ozone Map- ping Spectromet...The aerosol distribution in Beijing and peripheral cities agglomeration (BPCA) and its re- gional climatic effect are investigated on the basis of the statistical analyses of satellite Total Ozone Map- ping Spectrometer (TOMS) retrieval aerosol optical depth (AOD) and the meteorological data of sunshine duration, fog days, and low cloud cover, observed at Beijing and its peripheral meteorological stations. The analysis on multi-samples variational correction of the satellite remote sensing Moderate Resolution Imaging Spectroradiometer (MODIS) AOD under the clear sky and stable weather condition in conjunction with surface observations reveal that there was a “triangle-like” distribution pattern of the high values of aerosols in the southern “valley” of the “U-shape” megarelief of Beijing and its peripheral areas. The distribution pattern suggests that the large-scale transfer and diffusion of city agglomeration pollutants might form a relatively persistent characteristic spatial distribution of city agglomeration pollutants much larger than city-scale. Under the background of the particular megarelief effect of Beijing and periph- eral areas, the high value area of TOMS AOD, as well as regional correlation distribution between clear sky sunshine duration and TOMS AOD are also similar to the composite image of MODIS AOD variational fields, that is to say, the effect of atmospheric aerosols was very distinctive in Beijing and peripheral areas. The high value area of the negative correlation between clear sky sunshine duration and TOMS AOD ap-proximately accorded with the significant negative value area of the sunshine duration deviations of the 1980s to the 1990s, and the daily variations of the AOD also showed an anti-phase relation with those of clear sky sunshine duration. The above high cor- relation area of the urban aerosol impact of Beijing- Tianjin region leant towards south peripheral area, with its “center of gravity” in the south of Beijing- Tianjin agglomeration, and the main body of the high correlation area prolongating southwards, forming an aerosol influence domain of “eccentric ellipse” shape, that is to say, there was an aerosol influence domain of some “radius” in Beijing City and its peripheral areas, within and outside which sunshine duration, low cloud cover, and fog days showed a remarkable difference in interannual variation trend. At the downstream of the city agglomeration there was a significant interdecadal increment area of fog or low cloud cover, which might be associated with the local climatic feature of the regional flow convergent field in the diffusion process of city agglomeration pollut- ants in the aerosol influence domain, and such a local dynamical convergence feature might lead to the regional exacerbation of aerosol impact downstream of the city agglomeration. The research result reveals that the significant area of interdecadal change rate of low cloud cover within the aerosol influence do- main is correlated with the regional strengthening effect of aerosol impact of the local wind structure in the “downstream plume area” of the city.展开更多
Based on a comprehensive analysis on Sonic Anemometer and gradient data, wind profile radar(WPR) and GPS sounding data of March–August 2008 from the boundary layer(BL) tower observation system at Dali on the southeas...Based on a comprehensive analysis on Sonic Anemometer and gradient data, wind profile radar(WPR) and GPS sounding data of March–August 2008 from the boundary layer(BL) tower observation system at Dali on the southeastern edge of Tibetan Plateau(TP), it is found that the strengths of turbulent kinetic energy(TKE), buoyancy term and shear term depend on vegetation cover in association with local stability and thermodynamic condition. Strong kinetic turbulence appears when near surface layer in neutral condition with the large contribution from shear term. In an unstable condition within near surface layer, the atmospheric turbulent motion is mainly thermal turbulence, as buoyancy term is obviously larger than shear term. Under a stable condition the intermittent turbulence is accompanied by weak shear and buoyancy term, and TKE is significantly less than neutral or instable condition. The study also presents that the buoyancy term contribution at Nyingchi station in the southern slopes of the TP large topography in spring is significantly larger than that at Dali over the southeastern TP edge, reflecting that the thermal turbulence makes an important contribution to convection activity in the southern slopes of TP. Dali station is located in complex terrain with mountain and valley leading to larger kinetic turbulence. From the perspective of interaction of turbulence-convection in different scales, the study revealed that the height of convective boundary layer(CBL) could reach up to 1500–2000 m. TKE, shear term, and buoyancy term in near surface layer have the notable correlations with BL height and local vertical motion. The daytime thermodynamic turbulence effect of heat flux and buoyancy term has an obvious impact on the height of CBL, whereas mechanical turbulence only exerts a less impact. Mechanical turbulence in near surface layer has a significant impact on vertical motion especially in the forenoon with impacting height of 2500–3000 m. The peaks in diurnal variations of shear term and buoyancy term correspond to the high instable periods, especially in summer forenoon. Our observation analysis characterized the convection activity triggered by TKE source and their interaction in the southeastern TP edge.展开更多
To improve the numerical simulation of the severe snow storms occurred in the south of China and the middle/lower reaches of Changjiang River during January of 2008, the observations from the automatic weather station...To improve the numerical simulation of the severe snow storms occurred in the south of China and the middle/lower reaches of Changjiang River during January of 2008, the observations from the automatic weather stations (AWS) over the Qinghai-Xizang Plateau (QXP) and its surrounding areas were assimi-lated into the Weather Research and Forecasts (WRF) model using multi-cycle 3-dimensional varia-tional data assimilation (3DVAR). Due to the large-scale special topography of the QXP and its sur-rounding areas which may reach up to the mid-troposphere, the AWS located at different height on the deep slope of the plateau are different to those located on plains and take a role analogous in some extent to that of radio soundings in obtaining the vertical "profile" information of the atmosphere, and have the advantages in the aspects of sampling frequency, location/height fixing, and synchronization. The information captured by these AWS may carry the early-warning "strong signals" in the upstream sensitive area for the downstream weather systems to the east of the plateau and thus the assimilation of these AWS data is expected to lead to significant improvements on the simulation of the severe weather system occurred in its downstream areas through adjusting the 3-dimensional structures of the atmospheric thermal-dynamics for the initial conditions of the model. This study indicates that the assimilated information of moisture, temperature and pressure carried in the observations of AWS over the Qinghai-Xizang Plateau and its surrounding areas is very important and useful in the forecasting of precipitation in its downstream areas.展开更多
文摘采用WRF(Weather Research and Forecasting)模式4种边界层参数化方案对青藏高原那曲地区边界层特征进行了数值模拟,并利用"第三次青藏高原大气科学试验"在青藏高原那曲地区5个站点的观测资料对模拟结果进行验证,分析不同参数化方案在那曲地区的适用性。研究表明,YSU、MYJ、ACM2和BouLac方案对2 m气温和地表温度的模拟偏低。BouLac方案模拟的地表温度偏差较小。通过对能量平衡各分量的对比分析发现,温度模拟偏低可能是向下长波辐射模拟偏低以及感热通量和潜热通量交换过强导致的。对于边界层风、位温和相对湿度垂直结构的模拟,局地方案的模拟效果均优于非局地方案。BouLac方案对那曲地区近地层温度、边界层内位温和相对湿度的垂直分布模拟效果较好。
文摘中国中东部地区的空气污染主要集中在京津冀、长三角、珠三角、东北地区及汾渭平原等区域,各区域的污染排放特征各异.本文应用基于CMAQ(The Community Multiscale Air Quality)模式的自适应“nudging”源反演方法,反演中国中东部地区2016年12月—2017年1月逐日NOx污染源,分析上述主要污染区的污染物排放强度空间分布特征,并与2016年MEIC(The Multi-resolution emission inventory for China)排放源进行比较,检验反演源的可靠性.结果表明,2016年冬季各个区域反演源NOx排放强度空间分布特征与2016年MEIC排放源基本一致.京津冀地区高强度排放区域形成沿山前区域东北-西南走向的NOx高强度排放带;长三角地区NOx高强度排放区域位于常州、苏州、上海和湖州等城市构成的城市群;珠三角地区NOx高强度排放区域位于以广州为中心的大范围城市群且排放强度呈现向四周逐渐降低的放射状分布;东北地区NOx高强度排放区域空间分布特征呈现以城市为中心且稀疏分布;汾渭平原排放区域呈现以城市为中心且向峡谷中间集中分布,排放区域轮廓与汾渭平原狭长的新月状相符.
基金supported by the Ministry of Science and Technology of the People’s Republic of China (Grant No. G1999045700)the China Meteorological Administration Project (Grant No. CMATG2007Z04)
文摘This paper aims at constructing an emission source inversion model using a variational processing method and adaptive nudging scheme for the Community Multiscale Air Quality Model (CMAQ) based on satellite data to investigate the applicability of high resolution OMI (Ozone Monitoring Instrument) column concentration data for air quality forecasts over the North China. The results show a reasonable consistency and good correlation between the spatial distributions of NO2 from surface and OMI satellite measurements in both winter and summer. Such OMI products may be used to implement integrated variational analysis based on observation data on the ground. With linear and variational corrections made, the spatial distribution of OMI NO2 clearly revealed more localized distributing characteristics of NO2 concentration. With such information, emission sources in the southwest and southeast of North China are found to have greater impacts on air quality in Beijing. When the retrieved emission source inventory based on high-resolution OMI NO2 data was used, the coupled Weather Research Forecasting CMAQ model (WRF-CMAQ) performed significantly better in forecasting NO2 concentration level and its tendency as reflected by the more consistencies between the NO2 concentrations from surface observation and model result. In conclusion, satellite data are particularly important for simulating NO2 concentrations on urban and street-block scale. High-resolution OMI NO2 data are applicable for inversing NOx emission source inventory, assessing the regional pollution status and pollution control strategy, and improving the model forecasting results on urban scale.
基金supported by the National Natural Science Foundation of China (Grant No. 41130960)the National Science and Technology Pillar Program of China (Grant No. 2012BAK10B04)the National Department of Public Benefit Research Foundation of China (Grant No. GYHY201406001)
文摘Interannual variation of summer precipitation in East China, and frequency of rainstorms during the monsoon season from 1961 to 2010, are analyzed in this study. It is found that the two variables show opposite trends on a decadal time scale: frequency of rainstorms increases significantly after the 1990 s, while summer precipitation in East China decreases during the same period. Analysis of the spatial distribution of summer rainstorm frequency from 1961 to 2010 indicates that it decreases from the southeast to the northwest at the east edge of the large-scale topography associated with the plateaus. Spatial distribution of rainstorms with daily rainfall greater than 50 mm is characterized by a "high in the southeast and low in the northwest" pattern, similar to the staircase distribution of the topography. However, the spatial distribution of variation in both summer precipitation and frequency of extreme rainstorms under global warming differs significantly from the three-step staircase topography. It is shown that moisture characteristics of summer precipitation and extreme rainstorms during the monsoon season in East China, including moisture transport pathways, moist flow pattern, and spatial structure of the merging area of moist flows, differ significantly. Areas of frequent rainstorms include the Yangtze River Valley and South China. Column-integrated moisture transport and its spatial structure could be summarized as a "merging" of three branches of intense moist flows from low and middle latitude oceans, and "convergence" of column-integrated moisture fluxes. The merging area for moist flow associated with rainstorms in the high frequency region is located slightly to the south of the monsoonal precipitation or non-rainstorm precipitation, with significantly strong moisture convergence. In addition, the summer moist flow pattern in East China has a great influence on the frequency of extreme rainstorms. Moisture flux vectors in the region of frequent rainstorms correspond to vortical flow pattern. A comparison of moisture flux vectors associated with non-rainstorms and rainstorms indicates that the moist vortex associated with rainstorms is smaller in size and located to the south of the precipitation maximum, while the moist vortex associated with non-rainstorms is larger and located to the north. It is shown that column-integrated moist transport vortices and the structure of moist flux convergence have significant impacts on the north-south oscillation of frequent rainstorm areas in East China, which is synchronized with the maximum vorticity of moisture transport and the minimum of convergence on the decadal time scale. Synthesis of moisture transport pathways and related circulation impacts leads to a conceptual model of moisture flow associated with rainstorms.
基金Supported by the National Natural Science Foundation of China (Grant No. 90502003)the Major State Basic Research Development Program (Grant No. 2003CB716806)
文摘Tomé and Miranda’s climate trend turning discriminatory model is used to identify the spatial-temporal characteristics of the interdecadal turning of winter/summer climate modes at stations and in eight sub-areas over Chinese mainland based on the 1961–2000 observations. It is found that the stations with close occurrence years of the interdecadal trend turning (ITT) and coincident trends after the ITT exhibit a zonal distribution. A view is accordingly proposed that the interdecadal turnings of climate modes in China have remarkably regional structures. The research results show that after the early 1980s, winter climate over Chinese mainland overall trends towards a “warm-wet” mode, while summer climate had an abrupt change into “warm wet” mode in the late 1980s, suggesting that the time of the “warm-wet” mode turning for winter climate is earlier than that for summer climate. The regional characteristics and test results of the ITTs in eight sub-areas suggest that winter climate exhibits a distinctive “warm-dry” trend in North China after the late 1970s, and a slight “warm-dry” trend in Northeast China, South China, and Southwest China after the late 1980s. A “warm-wet” trend appears in the rest four sub-areas (the middle and lower reaches of the Yangtze River and the Huaihe River Valley, briefly Jianghuai, the east of the Tibetan plateau, and the east and west of Northwest China) after the early 1980s. The summer climate trends towards a “warm-dry” mode in Northeast China, North China and the east of Northwest China after the late 1980s, but a “warm-wet” mode appears in Southwest China and the east of the Tibetan plateau after the middle 1970s, as well as in Jianghuai and the west of Northwest China after the early 1980s. Specially, summer climate in South China started a “cold-wet” trend in 1984.
文摘This paper presents a comprehensive observa-tion technique on derived aerosols data from mobile sun-photometer graph and Terra-Moderate Resolution Imaging Spectroradiometer (MODIS) observation. Research results suggest that after being treated by the variational technique with respect to sunphotometer observations, the Terra- MODIS remote sensing aerosol data are remarkably im-proved, thus for the first time revealing features of the influ-ence of aerosols and pollution emissions of Beijing and its adjoining areas (Hebei, Shandong, etc. provinces). The re-gional impact features of aerosols are related with the pe-ripheral U-shape topography of Beijing. Analyses with Hy-brid Single Particle Lagrangian Integrated Trajectory model (HYSPLIT-4) and meteorological data in the case studied confirm the pollutants diffusion process along the trajectory from the sources in the south-west region, and the regional aerosol impact features.
文摘The aerosol distribution in Beijing and peripheral cities agglomeration (BPCA) and its re- gional climatic effect are investigated on the basis of the statistical analyses of satellite Total Ozone Map- ping Spectrometer (TOMS) retrieval aerosol optical depth (AOD) and the meteorological data of sunshine duration, fog days, and low cloud cover, observed at Beijing and its peripheral meteorological stations. The analysis on multi-samples variational correction of the satellite remote sensing Moderate Resolution Imaging Spectroradiometer (MODIS) AOD under the clear sky and stable weather condition in conjunction with surface observations reveal that there was a “triangle-like” distribution pattern of the high values of aerosols in the southern “valley” of the “U-shape” megarelief of Beijing and its peripheral areas. The distribution pattern suggests that the large-scale transfer and diffusion of city agglomeration pollutants might form a relatively persistent characteristic spatial distribution of city agglomeration pollutants much larger than city-scale. Under the background of the particular megarelief effect of Beijing and periph- eral areas, the high value area of TOMS AOD, as well as regional correlation distribution between clear sky sunshine duration and TOMS AOD are also similar to the composite image of MODIS AOD variational fields, that is to say, the effect of atmospheric aerosols was very distinctive in Beijing and peripheral areas. The high value area of the negative correlation between clear sky sunshine duration and TOMS AOD ap-proximately accorded with the significant negative value area of the sunshine duration deviations of the 1980s to the 1990s, and the daily variations of the AOD also showed an anti-phase relation with those of clear sky sunshine duration. The above high cor- relation area of the urban aerosol impact of Beijing- Tianjin region leant towards south peripheral area, with its “center of gravity” in the south of Beijing- Tianjin agglomeration, and the main body of the high correlation area prolongating southwards, forming an aerosol influence domain of “eccentric ellipse” shape, that is to say, there was an aerosol influence domain of some “radius” in Beijing City and its peripheral areas, within and outside which sunshine duration, low cloud cover, and fog days showed a remarkable difference in interannual variation trend. At the downstream of the city agglomeration there was a significant interdecadal increment area of fog or low cloud cover, which might be associated with the local climatic feature of the regional flow convergent field in the diffusion process of city agglomeration pollut- ants in the aerosol influence domain, and such a local dynamical convergence feature might lead to the regional exacerbation of aerosol impact downstream of the city agglomeration. The research result reveals that the significant area of interdecadal change rate of low cloud cover within the aerosol influence do- main is correlated with the regional strengthening effect of aerosol impact of the local wind structure in the “downstream plume area” of the city.
基金supported by the National Natural Science Foundation of China(Grant Nos.41130960,41165001,41175010)the China Special Fund for Meteorological Research in the Public Interest(Grant No.GYHY201406001)
文摘Based on a comprehensive analysis on Sonic Anemometer and gradient data, wind profile radar(WPR) and GPS sounding data of March–August 2008 from the boundary layer(BL) tower observation system at Dali on the southeastern edge of Tibetan Plateau(TP), it is found that the strengths of turbulent kinetic energy(TKE), buoyancy term and shear term depend on vegetation cover in association with local stability and thermodynamic condition. Strong kinetic turbulence appears when near surface layer in neutral condition with the large contribution from shear term. In an unstable condition within near surface layer, the atmospheric turbulent motion is mainly thermal turbulence, as buoyancy term is obviously larger than shear term. Under a stable condition the intermittent turbulence is accompanied by weak shear and buoyancy term, and TKE is significantly less than neutral or instable condition. The study also presents that the buoyancy term contribution at Nyingchi station in the southern slopes of the TP large topography in spring is significantly larger than that at Dali over the southeastern TP edge, reflecting that the thermal turbulence makes an important contribution to convection activity in the southern slopes of TP. Dali station is located in complex terrain with mountain and valley leading to larger kinetic turbulence. From the perspective of interaction of turbulence-convection in different scales, the study revealed that the height of convective boundary layer(CBL) could reach up to 1500–2000 m. TKE, shear term, and buoyancy term in near surface layer have the notable correlations with BL height and local vertical motion. The daytime thermodynamic turbulence effect of heat flux and buoyancy term has an obvious impact on the height of CBL, whereas mechanical turbulence only exerts a less impact. Mechanical turbulence in near surface layer has a significant impact on vertical motion especially in the forenoon with impacting height of 2500–3000 m. The peaks in diurnal variations of shear term and buoyancy term correspond to the high instable periods, especially in summer forenoon. Our observation analysis characterized the convection activity triggered by TKE source and their interaction in the southeastern TP edge.
基金Supported Jointly by National Natural Science Foundation of China (Grant Nos. 90502003 and 40625017)LaSW Project (Grant No. 2008LASWZI04)+1 种基金the Key Project of AMS (Grant No. 2008Z006)the JICA Program and the International Sci-Tech Cooperative Project (Grant No. 2007DFB20210)
文摘To improve the numerical simulation of the severe snow storms occurred in the south of China and the middle/lower reaches of Changjiang River during January of 2008, the observations from the automatic weather stations (AWS) over the Qinghai-Xizang Plateau (QXP) and its surrounding areas were assimi-lated into the Weather Research and Forecasts (WRF) model using multi-cycle 3-dimensional varia-tional data assimilation (3DVAR). Due to the large-scale special topography of the QXP and its sur-rounding areas which may reach up to the mid-troposphere, the AWS located at different height on the deep slope of the plateau are different to those located on plains and take a role analogous in some extent to that of radio soundings in obtaining the vertical "profile" information of the atmosphere, and have the advantages in the aspects of sampling frequency, location/height fixing, and synchronization. The information captured by these AWS may carry the early-warning "strong signals" in the upstream sensitive area for the downstream weather systems to the east of the plateau and thus the assimilation of these AWS data is expected to lead to significant improvements on the simulation of the severe weather system occurred in its downstream areas through adjusting the 3-dimensional structures of the atmospheric thermal-dynamics for the initial conditions of the model. This study indicates that the assimilated information of moisture, temperature and pressure carried in the observations of AWS over the Qinghai-Xizang Plateau and its surrounding areas is very important and useful in the forecasting of precipitation in its downstream areas.