The entrainment flux ratio Ae and the inversion layer (IL) thickness are two key parameters in a mixed layer model. Ae is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat ...The entrainment flux ratio Ae and the inversion layer (IL) thickness are two key parameters in a mixed layer model. Ae is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat flux. The IL is the layer between the mixed layer and the free atmosphere. In this study, a parameterization of Ae is derived from the TKE budget in the first- order model for a well-developed CBL under the condition of linearly sheared geostrophic velocity with a zero value at the surface. It is also appropriate for a CBL under the condition of geostrophic velocity remaining constant with height. LESs are conducted under the above two conditions to determine the coefficients in the parameterization scheme. Results suggest that about 43% of the shear-produced TKE in the IL is available for entrainment, while the shear-produced TKE in the mixed layer and surface layer have little effect on entrainment. Based on this scheme, a new scale of convective turbulence velocity is proposed and applied to parameterize the IL thickness, The LES outputs for the CBLs under the condition of linearly sheared geostrophic velocity with a non-zero surface value are used to verify the performance of the parameterization scheme. It is found that the parameterized Ae and IL thickness agree well with the LES outputs.展开更多
Following the parameterization of sheared entrainment obtained in the companion paper, Liu et al. (2016), the present study aims to further investigate the characteristics of entrainment, and develop a simple model ...Following the parameterization of sheared entrainment obtained in the companion paper, Liu et al. (2016), the present study aims to further investigate the characteristics of entrainment, and develop a simple model for predicting the growth rate of a well-developed and sheared CBL. The relative stratification, defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone, is found to be a function of entrainment flux ratio (Ae). This leads to a simple expression of the entrainment rate, in which Ae needs to be parameterized. According to the results in Liu et al. (2016), Ae can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL. The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations. Results indicate that the entrainment process is influenced by the dynamic effect, the interaction between mean shear and environmental stratification, and one other term that includes the Coriolis effect. These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL. This model is validated by outputs of LESs, and the results show that it performs satisfactorily. Compared with bulk models, this model does not need to solve a set of equations for the CBL. It is more convenient to apply in numerical models.展开更多
Based on observation data from urban observation stations in Nanjing and Suzhou at two heights in the roughness sublayer above the canopy and observation data at three heights in the SORPES station at the Xianlin Camp...Based on observation data from urban observation stations in Nanjing and Suzhou at two heights in the roughness sublayer above the canopy and observation data at three heights in the SORPES station at the Xianlin Campus of Nanjing University in a suburban area,the of land-atmosphere turbulent flux exchange and the energy balance over complex underlying surfaces were analyzed.The results indicated that in the roughness sublayer above the canopy,the nearsurface momentum flux,sensible heat flux,and latent heat flux increase with height,and the observation value of the surface albedo increases with height.However,the observation value of the net radiation decreases with height,thus resulting in a change in the urban surface energy budget with height.At the SORPES station in the Xianlin Campus of Nanjing University located in a hilly area,the momentum flux,sensible heat flux,and latent heat flux of the ground observation field significantly differed from those of the two heights on the tower,while the two heights on the tower were extremely close.These results indicate that the flux observation over the complex underlying surface exhibits adequate local only when it is conducted at a higher altitude above the ground.The turbulent flux observation results at a lower altitude in urban areas are underestimated,while the turbulent flux observation results near the surface produce a large deviation over the underlying hilly complex.展开更多
Organic aerosol(OA)is a major component of atmospheric particulate matter(PM)with complex composition and formation processes influenced by various factors.Emission reduction can alter both precursors and oxidants whi...Organic aerosol(OA)is a major component of atmospheric particulate matter(PM)with complex composition and formation processes influenced by various factors.Emission reduction can alter both precursors and oxidants which further affects secondary OA formation.Here we provide an observational analysis of secondary OA(SOA)variation properties in Yangtze River Delta(YRD)of eastern China in response to large scale of emission reduction during Chinese New Year(CNY)holidays from 2015 to 2020,and the COVID-19 pandemic period from January to March,2020.We found a 17%increase of SOA proportion during the COVID lockdown.The relative enrichment of SOA is also found during multi-year CNY holidays with dramatic reduction of anthropogenic emissions.Two types of oxygenated OA(OOA)influenced by mixed emissions and SOA formation were found to be the dominant components during the lockdown in YRD region.Our results highlight that these emission-reduction-induced changes in organic aerosol need to be considered in the future to optimize air pollution control measures.展开更多
A coupled aerosol–cloud model is essential for investigating the formation of haze and fog and the interaction of aerosols with clouds and precipitation. One of the key tasks of such a model is to produce correct mas...A coupled aerosol–cloud model is essential for investigating the formation of haze and fog and the interaction of aerosols with clouds and precipitation. One of the key tasks of such a model is to produce correct mass and number size distributions of aerosols. In this paper, a parameterization scheme for aerosol size distribution in initial emission,which took into account the measured mass and number size distributions of aerosols, was developed in the GRAPES–CUACE [Global/Regional Assimilation and Pr Ediction System–China Meteorological Administration(CMA) Unified Atmospheric Chemistry Environment model]—an online chemical weather forecast system that contains microphysical processes and emission, transport, and chemical conversion of sectional multi-component aerosols. In addition, the competitive mechanism between nucleation and condensation for secondary aerosol formation was improved, and the dry deposition was also modified to be in consistent with the real depositing length. Based on the above improvements, the GRAPES–CUACE simulations were verified against observational data during 1–31 January 2013, when a series of heavy regional haze–fog events occurred in eastern China. The results show that the aerosol number size distribution from the improved experiment was much closer to the observation, whereas in the old experiment the number concentration was higher in the nucleation mode and lower in the accumulation mode. Meanwhile, the errors in aerosol number size distribution as diagnosed by its sectional mass size distribution were also reduced. Moreover, simulations of organic carbon, sulfate, and other aerosol components were improved and the overestimation as well as underestimation of PM2.5 concentration in eastern China was significantly reduced,leading to increased correlation coefficient between simulated and observed PM2.5 by more than 70%. In the remote areas where bad simulation results were produced previously, the correlation coefficient grew from 0.35 to 0.61, and the mean mass concentration went up from 43% to 87.5% of the observed value. Thus, the simulation of particulate matters in these areas has been improved considerably.展开更多
基金sponsored by the National Natural Science Foundation of China(Grant No.40975004)the State Key Basic Program(973)Program(Grant No.2013CB430100)
文摘The entrainment flux ratio Ae and the inversion layer (IL) thickness are two key parameters in a mixed layer model. Ae is defined as the ratio of the entrainment heat flux at the mixed layer top to the surface heat flux. The IL is the layer between the mixed layer and the free atmosphere. In this study, a parameterization of Ae is derived from the TKE budget in the first- order model for a well-developed CBL under the condition of linearly sheared geostrophic velocity with a zero value at the surface. It is also appropriate for a CBL under the condition of geostrophic velocity remaining constant with height. LESs are conducted under the above two conditions to determine the coefficients in the parameterization scheme. Results suggest that about 43% of the shear-produced TKE in the IL is available for entrainment, while the shear-produced TKE in the mixed layer and surface layer have little effect on entrainment. Based on this scheme, a new scale of convective turbulence velocity is proposed and applied to parameterize the IL thickness, The LES outputs for the CBLs under the condition of linearly sheared geostrophic velocity with a non-zero surface value are used to verify the performance of the parameterization scheme. It is found that the parameterized Ae and IL thickness agree well with the LES outputs.
基金sponsored by the National Natural Science Foundation of China(Grant No.40975004)the State Key Basic Program(973)(Grant No.2013CB430100)
文摘Following the parameterization of sheared entrainment obtained in the companion paper, Liu et al. (2016), the present study aims to further investigate the characteristics of entrainment, and develop a simple model for predicting the growth rate of a well-developed and sheared CBL. The relative stratification, defined as the ratio of the stratification in the free atmosphere to that in the entrainment zone, is found to be a function of entrainment flux ratio (Ae). This leads to a simple expression of the entrainment rate, in which Ae needs to be parameterized. According to the results in Liu et al. (2016), Ae can be simply expressed as the ratio of the convective velocity scale in the sheared CBL to that in the shear-free CBL. The parameterization of the convective velocity scale in the sheared CBL is obtained by analytically solving the bulk model with several assumptions and approximations. Results indicate that the entrainment process is influenced by the dynamic effect, the interaction between mean shear and environmental stratification, and one other term that includes the Coriolis effect. These three parameterizations constitute a simple model for predicting the growth rate of a well-developed and sheared CBL. This model is validated by outputs of LESs, and the results show that it performs satisfactorily. Compared with bulk models, this model does not need to solve a set of equations for the CBL. It is more convenient to apply in numerical models.
基金supported by the National Key R&D Program of China(Grant No.2016YFC0200500)the Youth Project of National Natural Science Foundation of China(Grant No.41805007)。
文摘Based on observation data from urban observation stations in Nanjing and Suzhou at two heights in the roughness sublayer above the canopy and observation data at three heights in the SORPES station at the Xianlin Campus of Nanjing University in a suburban area,the of land-atmosphere turbulent flux exchange and the energy balance over complex underlying surfaces were analyzed.The results indicated that in the roughness sublayer above the canopy,the nearsurface momentum flux,sensible heat flux,and latent heat flux increase with height,and the observation value of the surface albedo increases with height.However,the observation value of the net radiation decreases with height,thus resulting in a change in the urban surface energy budget with height.At the SORPES station in the Xianlin Campus of Nanjing University located in a hilly area,the momentum flux,sensible heat flux,and latent heat flux of the ground observation field significantly differed from those of the two heights on the tower,while the two heights on the tower were extremely close.These results indicate that the flux observation over the complex underlying surface exhibits adequate local only when it is conducted at a higher altitude above the ground.The turbulent flux observation results at a lower altitude in urban areas are underestimated,while the turbulent flux observation results near the surface produce a large deviation over the underlying hilly complex.
基金supported by National Natural Science Foundation of China(No.42005082).
文摘Organic aerosol(OA)is a major component of atmospheric particulate matter(PM)with complex composition and formation processes influenced by various factors.Emission reduction can alter both precursors and oxidants which further affects secondary OA formation.Here we provide an observational analysis of secondary OA(SOA)variation properties in Yangtze River Delta(YRD)of eastern China in response to large scale of emission reduction during Chinese New Year(CNY)holidays from 2015 to 2020,and the COVID-19 pandemic period from January to March,2020.We found a 17%increase of SOA proportion during the COVID lockdown.The relative enrichment of SOA is also found during multi-year CNY holidays with dramatic reduction of anthropogenic emissions.Two types of oxygenated OA(OOA)influenced by mixed emissions and SOA formation were found to be the dominant components during the lockdown in YRD region.Our results highlight that these emission-reduction-induced changes in organic aerosol need to be considered in the future to optimize air pollution control measures.
基金Supported by the National Key Project of the Ministry of Science and Technology of China(2016YFC0203306)National Natural Science Foundation of China(91544232)+1 种基金National Science and Technology Support Program of China(2014BAC16B03)China Meteorological Administration Innovation Team Fund for Haze–Fog Monitoring and Forecasts
文摘A coupled aerosol–cloud model is essential for investigating the formation of haze and fog and the interaction of aerosols with clouds and precipitation. One of the key tasks of such a model is to produce correct mass and number size distributions of aerosols. In this paper, a parameterization scheme for aerosol size distribution in initial emission,which took into account the measured mass and number size distributions of aerosols, was developed in the GRAPES–CUACE [Global/Regional Assimilation and Pr Ediction System–China Meteorological Administration(CMA) Unified Atmospheric Chemistry Environment model]—an online chemical weather forecast system that contains microphysical processes and emission, transport, and chemical conversion of sectional multi-component aerosols. In addition, the competitive mechanism between nucleation and condensation for secondary aerosol formation was improved, and the dry deposition was also modified to be in consistent with the real depositing length. Based on the above improvements, the GRAPES–CUACE simulations were verified against observational data during 1–31 January 2013, when a series of heavy regional haze–fog events occurred in eastern China. The results show that the aerosol number size distribution from the improved experiment was much closer to the observation, whereas in the old experiment the number concentration was higher in the nucleation mode and lower in the accumulation mode. Meanwhile, the errors in aerosol number size distribution as diagnosed by its sectional mass size distribution were also reduced. Moreover, simulations of organic carbon, sulfate, and other aerosol components were improved and the overestimation as well as underestimation of PM2.5 concentration in eastern China was significantly reduced,leading to increased correlation coefficient between simulated and observed PM2.5 by more than 70%. In the remote areas where bad simulation results were produced previously, the correlation coefficient grew from 0.35 to 0.61, and the mean mass concentration went up from 43% to 87.5% of the observed value. Thus, the simulation of particulate matters in these areas has been improved considerably.