This numerical study of the Bohai Sea wintertime circulation by means of a two dimensional barotropic model with resolution of 1/24° in longitude and latitude showed that the Bohai Sea wintertime circulation is d...This numerical study of the Bohai Sea wintertime circulation by means of a two dimensional barotropic model with resolution of 1/24° in longitude and latitude showed that the Bohai Sea wintertime circulation is dominated by local monsoon winds. The major current components include the Bohai Warm Current, the North Shandong Coastal Current, and the Liaodong Gyre. The Bohai Warm Current originates from the Yellow Sea Warm Current at the northern part of Bohai Strait, meanders westwards and finally enters the northern part of Bohai Bay. The North Shandong Coastal Current flows along the southwest shore of Bohai Bay and Laizhou Bay and exits from the Bohai Sea through the south Bohai Strait. The anticyclonic Liaodong Gyre is located in the north of Liaodong Bay. A pair of eddies and the small scale Jinzhou Gyre are found between the Bohai Warm Current and the Liaodong Gyre. The computed volume transport for both the Bohai Warm Current and North Shandong Coastal Current is about 0.03 Sv (1 Sv=1×10 6 m 3/s). The numerical experiments showed that the combined effect of local monsoon winds and bottom topography dominate the formation of the circulation pattern. The Coriolis force and the wind stress curl are of certain importance. The beta effect, the momentum advection and the open boundary condition have little influence on the circulation pattern.展开更多
Previous measurements of peroxyacetyl nitrate （PAN） in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NOx, etc., mad...Previous measurements of peroxyacetyl nitrate （PAN） in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NOx, etc., made at an urban site （CMA） in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 × 10^-9 mol/mol （0.23 × 10^9-3.51 × 10^9 mol/mol） and was well correlated with that of NOa but not O3, indicating that the variations of the winter concentrations of PAN and O3 in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O3, PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O3, with an average PAN/O3 ratio smaller than 0.O31, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O3 ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O3 decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl （PA） radicai was estimated to be in the range of 0.0014 × 10^-12～0.0042 × 10^-12 mol/mol. The contributions of the formation reaction and thermal decomposition to PAN＇s variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition.展开更多
The high ridge in the northern branch of the subtropical westerly （hereafter referred to as northern branch ridge） extends from the north of the Tibetan Plateau to the north of Barr Kashmir Lake （32.5°-47.5...The high ridge in the northern branch of the subtropical westerly （hereafter referred to as northern branch ridge） extends from the north of the Tibetan Plateau to the north of Barr Kashmir Lake （32.5°-47.5°N, 70°-95°E） during wintertime. The intensity index and zonal position index of the wintertime northern branch ridge （WNBR） are defined in this study by using the NCEP-NCAR reanalysis data and precipitation and temperature observations at 160 stations in China. Interannual variation features of the WNBR and its relation with precipitation and surface air temperature in China are discussed based on wavelet analysis, correlation analysis, and composite analysis. The results indicate that the intensity and zonal position of the WNBR exhibit significant interannual variability. The intensity of the WNBR gradually weakens and varies in periodic cycles of 4-6, quasi-2, and quasi-16 yr. Its zonal position shifts westward slightly and varies in periodic cycles of quasi-8 and quasi-16 yr. The WNBR is highly correlated with precipitation and surface air temperature in China. When the WNBR is strong （weak） and its zonal position shifts eastward （westward）, winter precipitation in Northeast China and the northern region of Northwest China increases （decreases）, whereas precipitation decreases in central China, South China, and eastern regions of Northwest and Southwest China. Meanwhile, surface air temperatures in most areas of China are higher （lower） than normal. Further investigation has revealed that the two indexes are closely related to variations in general atmospheric circulation, which explains why there exists a close linkage between the variation of the WNBR and climate in China. It is believed that the WNBR is also tied to the Rossby wave, the North Atlantic Oscillation, the East Asian trough, and the North Pacific jet stream.展开更多
In conjunction with synchronous remotely sensed winds and sea surface temperature （SST）, the spatiotemporal features of the Zhe-Min coastal current （ZMCC）, especially responses of the ZMCC adjacent to Pingtan Isla...In conjunction with synchronous remotely sensed winds and sea surface temperature （SST）, the spatiotemporal features of the Zhe-Min coastal current （ZMCC）, especially responses of the ZMCC adjacent to Pingtan Island （PT） to the wintertime mon- soon relaxation in 2006 and corresponding mechanism are investigated based on the field observations. In situ data are ac- quired from Conductivity-Temperature-Depth （CTD） cruise and Bottom-Mounted Moorings （BMM）, which are conducted during a comprehensive survey for the Chinese Offshore Investigation and Assessment Project in winter 2006. It is revealed that the ZMCC is well mixed vertically in winter 2006. The ZMCC （〈14℃） recedes during the relaxation of the wintertime monsoon and is accompanied by the enhanced northward shift of the warm, saline Taiwan Strait Mixed Water （TSMW, higher than 14~C and is constituted by the Taiwan Strait Warm Water and the Kuroshio Branch Water）. And greatly enhanced south- ward intrusion of the ZMCC can be detected when the wintertime monsoon restores. Correspondingly, the thermal interface bounded by the ZMCC and the TSMW moves in the northwest/southeast direction, leading to periodic warm/cold reversals of the near-seabed temperature adjacent to the PT. By EOF （Empirical Orthogonal Function） analysis of the large-scale wind fields and wavelet power spectrum analysis of the water level, ocean current and the near-seabed temperature, responses of the ZMCC off the PT to wintertime monsoon relaxation are suggested to be attributed mainly to the southward propagating coast- ally trapped waves triggered by the impeding atmospheric fronts. As a result, ocean current and near-seabed temperature demonstrate significant quasi-5 d and quasi-10 d subtidal oscillations. By contrast, the onshore/offshore water accumulation resulted from Ekman advection driven by the local winds has minor contributions.展开更多
Precipitous Arctic sea-ice decline and the corresponding increase in Arctic open-water areas in summer months give more space for sea-ice growth in the subsequent cold seasons. Compared to the decline of the entire Ar...Precipitous Arctic sea-ice decline and the corresponding increase in Arctic open-water areas in summer months give more space for sea-ice growth in the subsequent cold seasons. Compared to the decline of the entire Arctic multiyear sea ice,changes in newly formed sea ice indicate more thermodynamic and dynamic information on Arctic atmosphere–ocean–ice interaction and northern mid–high latitude atmospheric teleconnections. Here, we use a large multimodel ensemble from phase 6 of the Coupled Model Intercomparison Project(CMIP6) to investigate future changes in wintertime newly formed Arctic sea ice. The commonly used model-democracy approach that gives equal weight to each model essentially assumes that all models are independent and equally plausible, which contradicts with the fact that there are large interdependencies in the ensemble and discrepancies in models' performances in reproducing observations. Therefore, instead of using the arithmetic mean of well-performing models or all available models for projections like in previous studies, we employ a newly developed model weighting scheme that weights all models in the ensemble with consideration of their performance and independence to provide more reliable projections. Model democracy leads to evident bias and large intermodel spread in CMIP6 projections of newly formed Arctic sea ice. However, we show that both the bias and the intermodel spread can be effectively reduced by the weighting scheme. Projections from the weighted models indicate that wintertime newly formed Arctic sea ice is likely to increase dramatically until the middle of this century regardless of the emissions scenario.Thereafter, it may decrease(or remain stable) if the Arctic warming crosses a threshold(or is extensively constrained).展开更多
The characteristics of wintertime volatile organic compounds(VOCs)in the North China Plain(NCP)region are complicated and remain obscure.VOC measurements were conducted by a proton transfer reaction time-of-flight mas...The characteristics of wintertime volatile organic compounds(VOCs)in the North China Plain(NCP)region are complicated and remain obscure.VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer(PTR-ToF-MS)at a rural site in the NCP from November to December 2018.Uncalibrated ions measured by PTRToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector(GC-MS/FID).The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions,the secondary formation of oxygenated VOCs(OVOCs)is non-negligible in the wintertime,i.e.,OVOCs accounts for 42%±7%in the total VOCs(151.3±75.6 ppbV).We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes.The chemical changes of organic carbon in a pollution accumulation period were investigated,which suggests an essential role of fragmentation reactions for large,chemically reduced compounds during the heavy-polluted stage in wintertime pollution.The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of“coal to gas”strategies in curbing air pollutants.The high abundances of some key species(e.g.oxygenated aromatics)indicate the strong emissions of coal combustion in wintertime of NCP.The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.展开更多
It is revealed that there happened a large am-plitude wintertime temperature anomaly reversion event(LTAR) in Northern Hemisphere high latitude regions andSouth Australia for the year 2003 versus 2002, with the mostno...It is revealed that there happened a large am-plitude wintertime temperature anomaly reversion event(LTAR) in Northern Hemisphere high latitude regions andSouth Australia for the year 2003 versus 2002, with the mostnotable change in Eurasia, eastern North America, NorthPacific, and South Australia. The accompanying atmosphericgeneral circulation anomalies are analyzed and the dominantchanges in the circulation arc found out. The anomalouscyclonic eddies over the north Pacific and the anomalousanticyclonic eddies over North Europe that cooperate eachother are mostly linked with the event. Both anomalous eddysystems are connected with the remote teleconnection pat-terns respectively. The research also suggests the existence ofa cross-equator teleconnection pattern, namely, the NorthernPacific-Western Pacific-Australia teleconnection pattern(NPWPA). It is not only related to LTAR, but also associatedwith the temperature transition from cold episode to warmepisode in the year 2003 versus 2002 during Decem-ber-January-February.展开更多
The paper presents a numerical two-dimensional model (with a realistic sea basin and wind fields as exter nal forcing) to simulate the basic features of the wintertime circulation in the Bohai and Huanghai (Yellow) Se...The paper presents a numerical two-dimensional model (with a realistic sea basin and wind fields as exter nal forcing) to simulate the basic features of the wintertime circulation in the Bohai and Huanghai (Yellow) Seas (BHS) and to show how the circulation can be driven by wind. The main results can be summarized as follows (1) The basic features of the BHS wintertime circulation can be depicted by the wind-driven barotropi’c motion. (2) The traditionally named Huanghai Sea Warm Current (HSWC) is actually generated by the north wind field, at least in winter. (3) The southward coastal current off the Korean west coast plays a more significant role in the southern Huanghai Sea wintertime circulation than traditionally believed. (4) Though the coastal landform and bottom topography play important roles in the wintertime BHS circulation pattern, the wind is a primary forcing.展开更多
The mechanism of the negative nighttime net CO2 flux in wintertime and reasonable treatment with it is of great importance in evaluating the carbon metabolism of boreal forest. Results, based on the data obtained with...The mechanism of the negative nighttime net CO2 flux in wintertime and reasonable treatment with it is of great importance in evaluating the carbon metabolism of boreal forest. Results, based on the data obtained with open-path eddy covariance system and CO2 profile measurement system from Nov. 2002 to Apr. 2003 and that obtained with five sonic anemometers in Nov. 1999, show that (1) the negative net ecosystem CO2 exchange flux (NEE) always appeared under conditions of strong wind; (2) the pressure fluctuation and horizontal advection flow are dominantly responsible for the negative NEE. Operable upper bound u* filtering method (UU* filtering) was introduced since the difficulties in real-time measuring of pressure fluctuation and horizontal advection fluxes under conditions of strong wind. Nighttime upper u*. threshold for the broad-leaved Korean pine mixed forest of the Changbai Mountains is 0.4 ms-1 and can be applied to the daytime filtering; and (3) the UU* filtering corrected the nighttime 'problem' of negative NEE under strong wind and made the estimates more ecologically reasonable.展开更多
Based on the snowfall observations at 836 surface weather stations in China and the Daily Surface Climate Variables of China version 3.0 dataset for 1961–2013, capability of five methods with different objective crit...Based on the snowfall observations at 836 surface weather stations in China and the Daily Surface Climate Variables of China version 3.0 dataset for 1961–2013, capability of five methods with different objective criteria for identifying wintertime snowfall is evaluated, to provide reference for application of these methods in snowfall/rainfall discrimination. Methods Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴuse the daily average surface air temperature(Ta), wet-bulb temperature(Tw), dynamic threshold Tw, 0-cm ground temperature, and 700–850-hPa thickness, respectively, to identify the snowfall. The results show that the climatological distribution of snowfall can be well produced by Methods Ⅰ, Ⅱ, and Ⅲ. Method Ⅳ underestimates the snowfall days in eastern Tibetan Plateau(ETP), and Method Ⅴ cannot yield the actual large numbers of snowfall days and amounts. Accordingly, the linear trends of snowfall days estimated from Methods Ⅰ, Ⅱ, and Ⅲ largely agree with the observations, while a discrepancy is found in the linear trend of snowfall amounts over southeastern China(SEC). For interannual and decadal variations of snowfall, Method Ⅴ shows the worst performance. It is more reasonable to use Tw to distinguish snowfall from rainfall instead of Ta, 0-cm ground temperature, and 700–850-hPa thickness;and the reference thresholds of Tw in northeastern China(NEC), northwestern China(NWC), ETP, and SEC are-1.5,-1.5,-0.4, and-0.3°C, respectively. The above results are beneficial to identifying snowfall in short-term climate prediction.展开更多
文摘This numerical study of the Bohai Sea wintertime circulation by means of a two dimensional barotropic model with resolution of 1/24° in longitude and latitude showed that the Bohai Sea wintertime circulation is dominated by local monsoon winds. The major current components include the Bohai Warm Current, the North Shandong Coastal Current, and the Liaodong Gyre. The Bohai Warm Current originates from the Yellow Sea Warm Current at the northern part of Bohai Strait, meanders westwards and finally enters the northern part of Bohai Bay. The North Shandong Coastal Current flows along the southwest shore of Bohai Bay and Laizhou Bay and exits from the Bohai Sea through the south Bohai Strait. The anticyclonic Liaodong Gyre is located in the north of Liaodong Bay. A pair of eddies and the small scale Jinzhou Gyre are found between the Bohai Warm Current and the Liaodong Gyre. The computed volume transport for both the Bohai Warm Current and North Shandong Coastal Current is about 0.03 Sv (1 Sv=1×10 6 m 3/s). The numerical experiments showed that the combined effect of local monsoon winds and bottom topography dominate the formation of the circulation pattern. The Coriolis force and the wind stress curl are of certain importance. The beta effect, the momentum advection and the open boundary condition have little influence on the circulation pattern.
基金supported by the China Special Fund for Meteorological Research in the Public Interest(No.GY-HY201206015,GYHY201106050)the Basic Research Fund of CAMS(2011Z003)the National Natural Science Foundation of China(No.40775074)
文摘Previous measurements of peroxyacetyl nitrate （PAN） in Asian megacities were scarce and mainly conducted for relative short periods in summer. Here, we present and analyze the measurements of PAN, O3, NOx, etc., made at an urban site （CMA） in Beijing from 25 January to 22 March 2010. The hourly concentration of PAN averaged 0.70 × 10^-9 mol/mol （0.23 × 10^9-3.51 × 10^9 mol/mol） and was well correlated with that of NOa but not O3, indicating that the variations of the winter concentrations of PAN and O3 in urban Beijing are decoupled with each other. Wind conditions and transport of air masses exert very significant impacts on O3, PAN, and other species. Air masses arriving at the site originated either from the boundary layer over the highly polluted N-S-W sector or from the free troposphere over the W-N sector. The descending free-tropospheric air was rich in O3, with an average PAN/O3 ratio smaller than 0.O31, while the boundary layer air over the polluted sector contained higher levels of PAN and primary pollutants, with an average PAN/O3 ratio of 0.11. These facts related with transport conditions can well explain the observed PAN-O3 decoupling. Photochemical production is important to PAN in the winter over Beijing. The concentration of the peroxyacetyl （PA） radicai was estimated to be in the range of 0.0014 × 10^-12～0.0042 × 10^-12 mol/mol. The contributions of the formation reaction and thermal decomposition to PAN＇s variation were calculated and found to be significant even in the colder period in air over Beijing, with the production exceeding the decomposition.
基金Supported by the National Natural Science Foundation of China(41275079,41305077,41405069,91537214,and 41505078)Scientific Research Fund for the Young Academic Leaders,Chengdu University of Information Technology(J201518 and J201516)
文摘The high ridge in the northern branch of the subtropical westerly （hereafter referred to as northern branch ridge） extends from the north of the Tibetan Plateau to the north of Barr Kashmir Lake （32.5°-47.5°N, 70°-95°E） during wintertime. The intensity index and zonal position index of the wintertime northern branch ridge （WNBR） are defined in this study by using the NCEP-NCAR reanalysis data and precipitation and temperature observations at 160 stations in China. Interannual variation features of the WNBR and its relation with precipitation and surface air temperature in China are discussed based on wavelet analysis, correlation analysis, and composite analysis. The results indicate that the intensity and zonal position of the WNBR exhibit significant interannual variability. The intensity of the WNBR gradually weakens and varies in periodic cycles of 4-6, quasi-2, and quasi-16 yr. Its zonal position shifts westward slightly and varies in periodic cycles of quasi-8 and quasi-16 yr. The WNBR is highly correlated with precipitation and surface air temperature in China. When the WNBR is strong （weak） and its zonal position shifts eastward （westward）, winter precipitation in Northeast China and the northern region of Northwest China increases （decreases）, whereas precipitation decreases in central China, South China, and eastern regions of Northwest and Southwest China. Meanwhile, surface air temperatures in most areas of China are higher （lower） than normal. Further investigation has revealed that the two indexes are closely related to variations in general atmospheric circulation, which explains why there exists a close linkage between the variation of the WNBR and climate in China. It is believed that the WNBR is also tied to the Rossby wave, the North Atlantic Oscillation, the East Asian trough, and the North Pacific jet stream.
基金supported by National Natural Science Foundation of China(Grant Nos.41176031 and 40806013)Chinese Offshore Physical Oceanography and Marine Meteorology Investigation and Assessment Project(Grant No.908-ZC-I-01)National Basic Research Program of China(Grant No:.2011CB403504).
文摘In conjunction with synchronous remotely sensed winds and sea surface temperature （SST）, the spatiotemporal features of the Zhe-Min coastal current （ZMCC）, especially responses of the ZMCC adjacent to Pingtan Island （PT） to the wintertime mon- soon relaxation in 2006 and corresponding mechanism are investigated based on the field observations. In situ data are ac- quired from Conductivity-Temperature-Depth （CTD） cruise and Bottom-Mounted Moorings （BMM）, which are conducted during a comprehensive survey for the Chinese Offshore Investigation and Assessment Project in winter 2006. It is revealed that the ZMCC is well mixed vertically in winter 2006. The ZMCC （〈14℃） recedes during the relaxation of the wintertime monsoon and is accompanied by the enhanced northward shift of the warm, saline Taiwan Strait Mixed Water （TSMW, higher than 14~C and is constituted by the Taiwan Strait Warm Water and the Kuroshio Branch Water）. And greatly enhanced south- ward intrusion of the ZMCC can be detected when the wintertime monsoon restores. Correspondingly, the thermal interface bounded by the ZMCC and the TSMW moves in the northwest/southeast direction, leading to periodic warm/cold reversals of the near-seabed temperature adjacent to the PT. By EOF （Empirical Orthogonal Function） analysis of the large-scale wind fields and wavelet power spectrum analysis of the water level, ocean current and the near-seabed temperature, responses of the ZMCC off the PT to wintertime monsoon relaxation are suggested to be attributed mainly to the southward propagating coast- ally trapped waves triggered by the impeding atmospheric fronts. As a result, ocean current and near-seabed temperature demonstrate significant quasi-5 d and quasi-10 d subtidal oscillations. By contrast, the onshore/offshore water accumulation resulted from Ekman advection driven by the local winds has minor contributions.
基金supported by the Chinese–Norwegian Collaboration Projects within Climate Systems jointly funded by the National Key Research and Development Program of China (Grant No.2022YFE0106800)the Research Council of Norway funded project,MAPARC (Grant No.328943)+2 种基金the support from the Research Council of Norway funded project,COMBINED (Grant No.328935)the National Natural Science Foundation of China (Grant No.42075030)the Postgraduate Research and Practice Innovation Program of Jiangsu Province (KYCX23_1314)。
文摘Precipitous Arctic sea-ice decline and the corresponding increase in Arctic open-water areas in summer months give more space for sea-ice growth in the subsequent cold seasons. Compared to the decline of the entire Arctic multiyear sea ice,changes in newly formed sea ice indicate more thermodynamic and dynamic information on Arctic atmosphere–ocean–ice interaction and northern mid–high latitude atmospheric teleconnections. Here, we use a large multimodel ensemble from phase 6 of the Coupled Model Intercomparison Project(CMIP6) to investigate future changes in wintertime newly formed Arctic sea ice. The commonly used model-democracy approach that gives equal weight to each model essentially assumes that all models are independent and equally plausible, which contradicts with the fact that there are large interdependencies in the ensemble and discrepancies in models' performances in reproducing observations. Therefore, instead of using the arithmetic mean of well-performing models or all available models for projections like in previous studies, we employ a newly developed model weighting scheme that weights all models in the ensemble with consideration of their performance and independence to provide more reliable projections. Model democracy leads to evident bias and large intermodel spread in CMIP6 projections of newly formed Arctic sea ice. However, we show that both the bias and the intermodel spread can be effectively reduced by the weighting scheme. Projections from the weighted models indicate that wintertime newly formed Arctic sea ice is likely to increase dramatically until the middle of this century regardless of the emissions scenario.Thereafter, it may decrease(or remain stable) if the Arctic warming crosses a threshold(or is extensively constrained).
基金supported by the National Key R&D Plan of China(No.2019YFE0106300)the National Natural Science Foundation of China(No.41877302)+3 种基金Guangdong Natural Science Funds for Distinguished Young Scholar(No.2018B030306037)Key-Area Research and Development Program of Guangdong Province(No.2019B110206001)Guangdong Innovative and Entrepreneurial Research Team Program(No.2016ZT06N263)supported by Special Fund Project for Science and Technology Innovation Strategy of Guangdong Province(No.2019B121205004)
文摘The characteristics of wintertime volatile organic compounds(VOCs)in the North China Plain(NCP)region are complicated and remain obscure.VOC measurements were conducted by a proton transfer reaction time-of-flight mass spectrometer(PTR-ToF-MS)at a rural site in the NCP from November to December 2018.Uncalibrated ions measured by PTRToF-MS were quantified and the overall VOC compositions were investigated by combining the measurements of PTR-ToF-MS and gas chromatography-mass spectrometer/flame ionization detector(GC-MS/FID).The measurement showed that although atmospheric VOCs concentrations are often dominated by primary emissions,the secondary formation of oxygenated VOCs(OVOCs)is non-negligible in the wintertime,i.e.,OVOCs accounts for 42%±7%in the total VOCs(151.3±75.6 ppbV).We demonstrated that PTR-MS measurements for isoprene are substantially overestimated due to the interferences of cycloalkanes.The chemical changes of organic carbon in a pollution accumulation period were investigated,which suggests an essential role of fragmentation reactions for large,chemically reduced compounds during the heavy-polluted stage in wintertime pollution.The changes of emission ratios of VOCs between winter 2011 and winter 2018 in the NCP support the positive effect of“coal to gas”strategies in curbing air pollutants.The high abundances of some key species(e.g.oxygenated aromatics)indicate the strong emissions of coal combustion in wintertime of NCP.The ratio of naphthalene to C8 aromatics was proposed as a potential indicator of the influence of coal combustion on VOCs.
文摘It is revealed that there happened a large am-plitude wintertime temperature anomaly reversion event(LTAR) in Northern Hemisphere high latitude regions andSouth Australia for the year 2003 versus 2002, with the mostnotable change in Eurasia, eastern North America, NorthPacific, and South Australia. The accompanying atmosphericgeneral circulation anomalies are analyzed and the dominantchanges in the circulation arc found out. The anomalouscyclonic eddies over the north Pacific and the anomalousanticyclonic eddies over North Europe that cooperate eachother are mostly linked with the event. Both anomalous eddysystems are connected with the remote teleconnection pat-terns respectively. The research also suggests the existence ofa cross-equator teleconnection pattern, namely, the NorthernPacific-Western Pacific-Australia teleconnection pattern(NPWPA). It is not only related to LTAR, but also associatedwith the temperature transition from cold episode to warmepisode in the year 2003 versus 2002 during Decem-ber-January-February.
基金This work was supported by the National Natural Science Foundation of China ,4860242
文摘The paper presents a numerical two-dimensional model (with a realistic sea basin and wind fields as exter nal forcing) to simulate the basic features of the wintertime circulation in the Bohai and Huanghai (Yellow) Seas (BHS) and to show how the circulation can be driven by wind. The main results can be summarized as follows (1) The basic features of the BHS wintertime circulation can be depicted by the wind-driven barotropi’c motion. (2) The traditionally named Huanghai Sea Warm Current (HSWC) is actually generated by the north wind field, at least in winter. (3) The southward coastal current off the Korean west coast plays a more significant role in the southern Huanghai Sea wintertime circulation than traditionally believed. (4) Though the coastal landform and bottom topography play important roles in the wintertime BHS circulation pattern, the wind is a primary forcing.
文摘The mechanism of the negative nighttime net CO2 flux in wintertime and reasonable treatment with it is of great importance in evaluating the carbon metabolism of boreal forest. Results, based on the data obtained with open-path eddy covariance system and CO2 profile measurement system from Nov. 2002 to Apr. 2003 and that obtained with five sonic anemometers in Nov. 1999, show that (1) the negative net ecosystem CO2 exchange flux (NEE) always appeared under conditions of strong wind; (2) the pressure fluctuation and horizontal advection flow are dominantly responsible for the negative NEE. Operable upper bound u* filtering method (UU* filtering) was introduced since the difficulties in real-time measuring of pressure fluctuation and horizontal advection fluxes under conditions of strong wind. Nighttime upper u*. threshold for the broad-leaved Korean pine mixed forest of the Changbai Mountains is 0.4 ms-1 and can be applied to the daytime filtering; and (3) the UU* filtering corrected the nighttime 'problem' of negative NEE under strong wind and made the estimates more ecologically reasonable.
基金Supported by the National Key Research and Development Program of China(2016YFA0600702)National Natural Science Foundation of China(41625019)。
文摘Based on the snowfall observations at 836 surface weather stations in China and the Daily Surface Climate Variables of China version 3.0 dataset for 1961–2013, capability of five methods with different objective criteria for identifying wintertime snowfall is evaluated, to provide reference for application of these methods in snowfall/rainfall discrimination. Methods Ⅰ, Ⅱ, Ⅲ, Ⅳ, and Ⅴuse the daily average surface air temperature(Ta), wet-bulb temperature(Tw), dynamic threshold Tw, 0-cm ground temperature, and 700–850-hPa thickness, respectively, to identify the snowfall. The results show that the climatological distribution of snowfall can be well produced by Methods Ⅰ, Ⅱ, and Ⅲ. Method Ⅳ underestimates the snowfall days in eastern Tibetan Plateau(ETP), and Method Ⅴ cannot yield the actual large numbers of snowfall days and amounts. Accordingly, the linear trends of snowfall days estimated from Methods Ⅰ, Ⅱ, and Ⅲ largely agree with the observations, while a discrepancy is found in the linear trend of snowfall amounts over southeastern China(SEC). For interannual and decadal variations of snowfall, Method Ⅴ shows the worst performance. It is more reasonable to use Tw to distinguish snowfall from rainfall instead of Ta, 0-cm ground temperature, and 700–850-hPa thickness;and the reference thresholds of Tw in northeastern China(NEC), northwestern China(NWC), ETP, and SEC are-1.5,-1.5,-0.4, and-0.3°C, respectively. The above results are beneficial to identifying snowfall in short-term climate prediction.
