Aerodynamic roughness length (Z0m) is a key factor in surface flux estimations with remote sensing algorithms and/or land surface models. This paper calculates ZOrn over several land surfaces, with 3 years of experi...Aerodynamic roughness length (Z0m) is a key factor in surface flux estimations with remote sensing algorithms and/or land surface models. This paper calculates ZOrn over several land surfaces, with 3 years of experimental data from Xiaotangshan. The results show that Z0m is direction-dependent, mainly due to the heterogeneity of the size and spatial distribution of the roughness elements inside the source area along different wind directions. Furthermore, a heuristic parameterization of the aerodynamic roughness length for heterogeneous surfaces is proposed. Individual Z0m over each surface component (patch) is calculated firstly with the characteristic parameters of the roughness elements (vegetation height, leaf area index, etc.), then Z0m over the whole experimental field is aggregated, using the footprint weighting method.展开更多
It has previously been shown that aerodynamic roughness length changes significantly along with near- surface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very l...It has previously been shown that aerodynamic roughness length changes significantly along with near- surface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very little research concerning this topic has been conducted. In this paper, by using the data of different underlying surfaces provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, aerodynamic roughness length (z0) values in stable, neutral, and unstable atmospheric stratifications are compared with one another, and the relationship between z0 and atmospheric thermodynamic stability (() is analyzed. It is found that z0 shows great differences among the stable, neutral, and unstable atmospheric thermodynamic states, with the difference in z0 values between the fully thermodynamic stable condition and the neutral condition reaching 60% of the mean z0. F^trthermore, for the wind speed range in which the wind data are less sensitive to z0, the surface z0 changes more significantly with (, and is highly correlated with both the Monin-Obukhov stability (4o) and the overall Richardson number (Rib), with both of their correlation coefficients greater than 0.71 and 0.47 in the stable and unstable atmospheric stratification, respectively. The empirical relation fitted with the experimental observations is quite consistent with the Zilitinkevich theoretical relation in the stable atmosphere, but the two are quite distinct and even show opposite variation tendencies in the unstable atmosphere. In application, however, verification of the empirical fitted relations by using the experimental data finds that the fitted relation is slightly more applicable than the Zilitinkevich theoretical relation in stable atmospheric stratification, but it is much more suitable than the Zilitinkevich relation in unstable atmospheric stratification.展开更多
Over Antarctica,surface fluxes play an important role in the local atmospheric dynamical processes.To reveal the surface fluxes characteristics and aerodynamic and thermal roughness lengths over Zhongshan station,Anta...Over Antarctica,surface fluxes play an important role in the local atmospheric dynamical processes.To reveal the surface fluxes characteristics and aerodynamic and thermal roughness lengths over Zhongshan station,Antarctica,this paper analyzes the data observed at the station during 3 March 2008 through 15 February 2009.It is found that easterlies dominated this site throughout the whole year,with a maximum(average)speed of 25(5.6)m s−1 at 3.9 m height,and the annual maximum(minimum)surface temperature reached 291.05(230.05)K,while the annual maximum(minimum)air-specific humidity was 4.1(0.05)g/kg at 3.9 m height.The maximum(minimum)values of seasonal mean temperature,humidity,each radiation components,sensible and latent heat flux occurred in summer(winter),while for the seasonal averaged wind speed andτthe minimums(maximums)appeared in summer(autumn).After comparing with a partially linear regression method for aerodynamic roughness length and four previous equations that derive thermal roughness length from surface Reynolds number,constant values of aerodynamic roughness length as 3.6×10^(−3)m and thermal roughness length as 1.2×10^(−4)m at this site were validated by using the other three level observations and suggested for future studies.展开更多
基金supported by the Hi-tech Research and Development Program of China(2007AA12Z175)the Special Research Foundation of the Public Benefit Industry (GYHY200706046)+1 种基金the Project funded by the National Natural Science Foundation of China (Grant No. 40671128)the National Basic Research Program of China (2007CB714401)
文摘Aerodynamic roughness length (Z0m) is a key factor in surface flux estimations with remote sensing algorithms and/or land surface models. This paper calculates ZOrn over several land surfaces, with 3 years of experimental data from Xiaotangshan. The results show that Z0m is direction-dependent, mainly due to the heterogeneity of the size and spatial distribution of the roughness elements inside the source area along different wind directions. Furthermore, a heuristic parameterization of the aerodynamic roughness length for heterogeneous surfaces is proposed. Individual Z0m over each surface component (patch) is calculated firstly with the characteristic parameters of the roughness elements (vegetation height, leaf area index, etc.), then Z0m over the whole experimental field is aggregated, using the footprint weighting method.
基金Supported by the National Natural Science Foundation of China (40830957, 41075008, and 41075009)National Basic Research and Development (973) Program of China (2013CB430206)China Postdoctoral Science Foundation (20110490854)
文摘It has previously been shown that aerodynamic roughness length changes significantly along with near- surface atmospheric thermodynamic state; however, at present, this phenomenon remains poorly understood, and very little research concerning this topic has been conducted. In this paper, by using the data of different underlying surfaces provided by the Experimental Co-observation and Integral Research in Semi-arid and Arid Regions over North China, aerodynamic roughness length (z0) values in stable, neutral, and unstable atmospheric stratifications are compared with one another, and the relationship between z0 and atmospheric thermodynamic stability (() is analyzed. It is found that z0 shows great differences among the stable, neutral, and unstable atmospheric thermodynamic states, with the difference in z0 values between the fully thermodynamic stable condition and the neutral condition reaching 60% of the mean z0. F^trthermore, for the wind speed range in which the wind data are less sensitive to z0, the surface z0 changes more significantly with (, and is highly correlated with both the Monin-Obukhov stability (4o) and the overall Richardson number (Rib), with both of their correlation coefficients greater than 0.71 and 0.47 in the stable and unstable atmospheric stratification, respectively. The empirical relation fitted with the experimental observations is quite consistent with the Zilitinkevich theoretical relation in the stable atmosphere, but the two are quite distinct and even show opposite variation tendencies in the unstable atmosphere. In application, however, verification of the empirical fitted relations by using the experimental data finds that the fitted relation is slightly more applicable than the Zilitinkevich theoretical relation in stable atmospheric stratification, but it is much more suitable than the Zilitinkevich relation in unstable atmospheric stratification.
基金the National Natural Science Foundation of China(Grant Nos.41376005 and 41505004)the National Key Projects of Ministry of Science and Technology of China(2016YFA0602100)+1 种基金the Chinese Polar Environmental Comprehensive Investigation and Assessment Program,and the Open Project Program(KLME1508)the Key Laboratory of Meteorological Disaster of Ministry of Education at Nanjing University of Information Science and Technology。
文摘Over Antarctica,surface fluxes play an important role in the local atmospheric dynamical processes.To reveal the surface fluxes characteristics and aerodynamic and thermal roughness lengths over Zhongshan station,Antarctica,this paper analyzes the data observed at the station during 3 March 2008 through 15 February 2009.It is found that easterlies dominated this site throughout the whole year,with a maximum(average)speed of 25(5.6)m s−1 at 3.9 m height,and the annual maximum(minimum)surface temperature reached 291.05(230.05)K,while the annual maximum(minimum)air-specific humidity was 4.1(0.05)g/kg at 3.9 m height.The maximum(minimum)values of seasonal mean temperature,humidity,each radiation components,sensible and latent heat flux occurred in summer(winter),while for the seasonal averaged wind speed andτthe minimums(maximums)appeared in summer(autumn).After comparing with a partially linear regression method for aerodynamic roughness length and four previous equations that derive thermal roughness length from surface Reynolds number,constant values of aerodynamic roughness length as 3.6×10^(−3)m and thermal roughness length as 1.2×10^(−4)m at this site were validated by using the other three level observations and suggested for future studies.