Turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames. Performances of three methods of coordinate rotation： double rotation （DR...Turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames. Performances of three methods of coordinate rotation： double rotation （DR）, triple rotation （TR）, and classic planar-fit rotation （PF） were examined in terms of correction of eddy covariance flux. Using the commonly used DR and TR methods, unreasonable rotation angles are encountered at low wind speeds and cause significant run-to-run errors of some turbulence characteristics. The PF method rotates the coordinate system to an ensemble-averaged plane, and shows large tilt error due to an inaccurate fit plane over variable terrain slopes. In this paper, we propose another coordinate rotation scheme. The observational data were separated into two groups according to wind direction. The PF method was adapted to find an ensemble-averaged streamline plane for each group of hourly runs with wind speed exceeding 1.0 m s-1. Then, the coordinate systems were rotated to their respective best- fit planes for all available hourly observations. We call this the PF10 method. The implications of tilt corrections for the turbulence characteristics are discussed with a focus on integral turbulence characteristics, the spectra of wind-velocity components, and sensible heat and momentum fluxes under various atmospheric stabilities. Our results show that the adapted application of PF provides greatly improved estimates of integral turbulence characteristics in complex terrain and maintains data quality. The comparisons of the sensible heat fluxes for four coordinate rotation methods to fluxes before correction indicate that the PF10 scheme is the best to preserve consistency between fluxes.展开更多
The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. T...The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g.m^-2.month ^-1 in June 2004 （simplified expression of g （carbon）.m^-2.month^-1） and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g-m^-2.a^-1 （simplified expression of g （carbon）.m^-2.a^-1） during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit （VPD） and temperature. Under humid conditions （VPD 〈 1.0 kPa）, the gross ecosystem production （GEP） increased with increasing temperature. But the net ecosystem production （NEP） showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment （VPD 〉 1.0 kPa）, the GEP decreased with the increasing VPD at a rate of 3.0 μmol.m^-2.s^-1kPa -1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol.m^-2.s-1.kPa^-1. Under humid conditions （VPD 〈 1.0 kPa）, both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range.展开更多
To understand the CH_(4) flux variations and their climatic drivers in the rice-wheat agroecosystem in the Huai River Basin of China,the CH_(4) flux was observed by using open-path eddy covariance at a typical rice-wh...To understand the CH_(4) flux variations and their climatic drivers in the rice-wheat agroecosystem in the Huai River Basin of China,the CH_(4) flux was observed by using open-path eddy covariance at a typical rice-wheat rotation system in Anhui Province,China from November 2019 to October 2021.The variations and their drivers were then analyzed with the Akaike information criterion method.CH_(4) flux showed distinct diurnal variations with single peaks during 9:00-13:00 local time.The highest peak was 2.15μg m^(-2)s^(-1)which occurred at 11:00 in the vegetative growth stage in the rice growing season(RGS).CH_(4) flux also showed significant seasonal variations.The average CH_(4)flux in the vegetative growth stage in the RGS(193.8±74.2 mg m^(-2)d^(-1))was the highest among all growth stages.The annual total CH_(4) flux in the non-rice growing season(3.2 g m^(-2))was relatively small compared to that in the RGS(23.9 g m^(-2)).CH_(4) flux increased significantly with increase in air temperature,soil temperature,and soil water content in both the RGS and the non-RGS,while it decreased significantly with increase in vapor pressure deficit in the RGS.This study provided a comprehensive understanding of the CH_(4) flux and its drivers in the rice-wheat rotation agroecosystem in the Huai River Basin of China.In addition,our findings will be helpful for the validation and adjustment of the CH_(4) models in this region.展开更多
A flexible polarization demultiplexing method based on an adaptive Kalman filter（AKF） is proposed in which the process noise covariance has been estimated adaptively. The proposed method may significantly improve th...A flexible polarization demultiplexing method based on an adaptive Kalman filter（AKF） is proposed in which the process noise covariance has been estimated adaptively. The proposed method may significantly improve the adaptive capability of an extended Kalman filter（EKF） by adaptively estimating the unknown process noise covariance. Compared to the conventional EKF, the proposed method can avoid the tedious and time consuming parameter-by-parameter tuning operations. The effectiveness of this method is confirmed experimentally in 128 Gb/s 16 QAM polarization-division-multiplexing（PDM） coherent optical transmission systems. The results illustrate that our proposed AKF has a better tracking accuracy and a faster convergence（about 4 times quicker）compared to a conventional algorithm with optimal process noise covariance.展开更多
Measurement of turbulence fluxes were performed over the Erhai Lake using eddy covariance(EC) method.Basic physical parameters in the lake-air interaction processes,such as surface albedo of the lake,aerodynamic rough...Measurement of turbulence fluxes were performed over the Erhai Lake using eddy covariance(EC) method.Basic physical parameters in the lake-air interaction processes,such as surface albedo of the lake,aerodynamic roughness length,bulk transfer coefficients,etc.,were investigated using the EC data in 2012.The characteristics of turbulence fluxes over the lake including momentum flux,sensible heat flux,latent heat flux,and CO2 flux,and their controlling factors were analyzed.The total annual evaporation of the lake was also estimated based on the artificial neural network(ANN) gap-filling technique.Results showed that the total annual evaporation in 2012 was 1165 ± 15 mm,which was larger than the annual precipitation(818 mm).Local circulation between the lake and the surrounding land was found to be significant throughout the year due to the land-lake breeze or the mountain-valley breeze in this area.The prevailing winds of southeasterly and northwesterly were observed throughout the year.The sensible heat flux over this plateau lake usually had a few tens of W m-2,and generally became negative in the afternoon,indicating that heat was transferred from the lake to the atmosphere.The sensible heat flux was governed by the lake-air temperature difference and had its maximum in the early morning.The diurnal variation of the latent heat flux was controlled by vapor pressure deficit with a peak in the afternoon.The latent heat flux was dominant in the partition of available energy in daytime over this lake.The lake acted as a weak CO2 source to the atmosphere except for the midday of summer.Seasonal variations of surface albedo over the lake were related to the solar elevation angle and opacity of the water.Furthermore,compared with the observation data,the surface albedo estimated by CLM4-LISSS model was underestimated in winter and overestimated in summer.展开更多
Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteor...Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteorological profile observation data were used to analyze characteristics of these parameters on the diurnal, seasonal, and annual scales. Significant seasonal and annual variations of the aerodynamic roughness length are observed over the two surfaces. A large variation of kB-1 is measured during the day. Both kB-1 and the bulk transfer coefficients exhibit significant seasonal and annual variations. During the growing season (May to October), average Cd and Ch are 3.1×10-3 and 2.5×10-3 over the degrade grassland surface, and 4.7×10-3 and 3.1×10-3 over the cropland surface respectively. During the non-growing season, average Cd and Ch are 2.3×10-3 and 2.0×10-3 over the degrade grassland surface, and 2.9×10-3 and 2.2×10-3 over the cropland surface respectively.展开更多
Based on the light-photosynthesis response measurement at leaf level,combined with over-and under-canopy eddy covariance measurements,research on photosynthetic characteristics of single trees and forest canopy was co...Based on the light-photosynthesis response measurement at leaf level,combined with over-and under-canopy eddy covariance measurements,research on photosynthetic characteristics of single trees and forest canopy was conducted.The relationship between light intensity and photo-synthetic rates for leaves and canopy can be well fitted by a non-rectangular hyperbola model.Mongolian oak presented a high light compensation point,Lcp(28μmol·m-2·s-1),a light saturation point Lsp(>1800μmol·m-2·s-1),and a maximal net photosynthetic rate Pmax(9.96μmol·m-2·s-1),which suggest that it is a typical heliophilous plant.Mono maple presented the highest apparent quantum efficiencyα(0.066)but the lowest,Lcp(16μmol·m-2·s-1),Lsp(=800μmol·m-2·s-1),and Pmax(4.51μmol·m-2·s-1),which suggest that it is heliophilous plant.Korean pine showed the lowestαvalue but a higher Pmax,which suggest that it is a semi-heliophilous plant.At the canopy level,the values of both or and Pmax approached the upper limit of reported values in temperate forests,while Lcp was within the lower limit.Canopy photosynthetic characteristics were well consistent with those of leaves.Both showed a high ability to photosynthesize.However,environmental stresses,especially high vapor pressure deficits,could significantly reduce the photosynthetic ability of leaves and canopy.展开更多
Based on analysis of mechanisms causing energy no-closure and nocturnal low fluxes issues for CO_(2) exchange studies by eddy covariance method,corrections were done with the raw data sets obtained from Changbai Mount...Based on analysis of mechanisms causing energy no-closure and nocturnal low fluxes issues for CO_(2) exchange studies by eddy covariance method,corrections were done with the raw data sets obtained from Changbai Mountains forest flux site,to evaluate the impacts of sonic anemometer tilt,frequency response limitations and advection on estimation of CO_(2) exchange,respectively.The results show that the planar fit coordinate transforming method is superior to the streamline coordinate transforming method in tilt correction.The latter could cause a systematical underestimation of eddy fluxes relating with the angle of sensor and terrain tilt.The underestimation of CO_(2) and energy fluxes for frequency response limitations average 3.0%and 2.0%during daytime,respectively,which increase by 9.0%and 5.5%during nighttime,respectively.The corrections of frequency response limitations are closely related to atmospheric stability.The advection loss of CO_(2) fluxes is dominated by nocturnal vertical advection,which is at least 18%when the horizontal advection is neglected.It is suggested that more work be done to understand the characteristics of horizontal advection and turbulent eddies under a complexcircumstance.展开更多
The results of eddy covariance observation system could represent the physical process at certain area of the surface.Thus point-to-area representativeness was of primary interest in flux observation.This research pre...The results of eddy covariance observation system could represent the physical process at certain area of the surface.Thus point-to-area representativeness was of primary interest in flux observation.This research presents a preliminary study for flux observation at ChinaFLUX sites by the use of observation data and Flux Source Area Model(FSAM).Results show that the footprint expands and is further away from flux tower when atmosphere becomes more stable,the observation height increases,or the surfaces become smoother.This suggests that the area represented by the flux observation becomes larger.The distances from the reference point to the maximum point Smax and the minimum point x1 of source weight function(Dmax and Dmin,respectively)can be influenced by atmosphere stability which becomes longer when atmosphere is more stable.For more rough surfaces and lower observation point Dmax and Dmin become shorter.This research gives the footprint at level P=90%at ChinaFLUX sites at different atmosphere stability.The preliminary results of spatial representiveness at ChinaFLUX sites were given based on the dominant wind direction and footprint response to various factors.The study also provides some theoretical basis for data quality control and evaluating data uncertainty.展开更多
Based on the carbon fluxes measured over the grassland ecosystems in Inner Mongolia （UG79 site）, Loess Plateau （SACOL site）, and Tongyu, Jilin Province （TY site） in the semiarid areas from 2007 to 2008 with the ...Based on the carbon fluxes measured over the grassland ecosystems in Inner Mongolia （UG79 site）, Loess Plateau （SACOL site）, and Tongyu, Jilin Province （TY site） in the semiarid areas from 2007 to 2008 with the eddy covariance method, we have investigated the carbon exchange processes over semiarid grassland ecosystem and its main affecting environmental variables. The precipitations at UG79 and TY sites in 2007 were below the historical average, especially for TY site, which was 50% be- low the historical average annual precipitation. The precipitation in SACOL site was close to average in 2007 but below average in 2008. The variation of monthly diurnal average NEE showed that the diurnal mean NEE decreased in the order of TY site, UG79 site, and SACOL site. However, a longer net carbon uptake period was observed at SACOL site. The diurnal course of NEE at UG79 site was similar between 2007 and 2008. The diurnal average NEE remained large during July and August in growing sea- son （May to September） at UG79 site, with maximum values approaching 0.08 mg C m^-2 s^-1 in August of 2008. The diurnal av- erage NEE of 2007 was larger than 2008 at SACOL site, with maximum values of 0.07 mg C m^-2 sq in September of 2007. A shorter carbon uptake period was recorded in 2007 at TY site, lasting from July to August. A larger diurnal average NEE oc- curred in 2008 at TY site, with maximum values of 0.12 mg C m^-2 s^-1. The ecosystem respirations of three sites were controlled by both soil temperature and soil volumetric water content （at a depth of 5 cm below the land surface）. Both UG79 site and SACOL site acted as a carbon sink during the growing periods of 2007 and 2008. Annual NEE in the growing seasons of 2007 and 2008 ranged from -68 to -50 g C m^-2 at UG79 site and from -109 to -55 g C m^-2at SACOL site. Alternation between car- bon source and carbon sink was found at TY site, with respective values of annual NEE in the growing seasons of 0.32 g C m^-2 and -73 g C m^-2 in 2007 and 2008. The magnitude and duration of carbon uptake depended mainly on the amount and timing of precipitation and the timing of the first effective rainfall during the growing season in semiarid grassland ecosystems.展开更多
Mainly.three methods have been developed to calculate turbulence heat flux.They are eddy covariance method,Bowen ratio/energy balance method and aerodynamic method.In this paper, all the three methods have been used t...Mainly.three methods have been developed to calculate turbulence heat flux.They are eddy covariance method,Bowen ratio/energy balance method and aerodynamic method.In this paper, all the three methods have been used to calculate sensible heat flux,latent heat flux and imbalance energy near the surface with the experiment data of EBEX-2000.Then comparisons of the three methods and some possible explanations of the surface imbalance energy are given.展开更多
基金supported by the National High Technology Research and Development Program of China(Grant No.2007AA022201)the National Special Fund for Water(Grant No.2008ZX07103007)+1 种基金the National Basic Research Program of China (Grant Nos.2010CB428503 and 2011CB403406)the National Natural Science Foundation of China(Grant Nos. 40805006 and 41075012)
文摘Turbulence characteristics of an atmospheric surface layer over a coastal mountain area were investigated under different coordinate frames. Performances of three methods of coordinate rotation： double rotation （DR）, triple rotation （TR）, and classic planar-fit rotation （PF） were examined in terms of correction of eddy covariance flux. Using the commonly used DR and TR methods, unreasonable rotation angles are encountered at low wind speeds and cause significant run-to-run errors of some turbulence characteristics. The PF method rotates the coordinate system to an ensemble-averaged plane, and shows large tilt error due to an inaccurate fit plane over variable terrain slopes. In this paper, we propose another coordinate rotation scheme. The observational data were separated into two groups according to wind direction. The PF method was adapted to find an ensemble-averaged streamline plane for each group of hourly runs with wind speed exceeding 1.0 m s-1. Then, the coordinate systems were rotated to their respective best- fit planes for all available hourly observations. We call this the PF10 method. The implications of tilt corrections for the turbulence characteristics are discussed with a focus on integral turbulence characteristics, the spectra of wind-velocity components, and sensible heat and momentum fluxes under various atmospheric stabilities. Our results show that the adapted application of PF provides greatly improved estimates of integral turbulence characteristics in complex terrain and maintains data quality. The comparisons of the sensible heat fluxes for four coordinate rotation methods to fluxes before correction indicate that the PF10 scheme is the best to preserve consistency between fluxes.
基金the Global Environment Research Fund,Ministry of the Environment,Japan (S-1: Integrated Study for Terrestrial Carbon Management of Asia in the 21st Century Based on Scientific Advancements)the Chinese Academy of Sciences (07W70000SZ)+1 种基金the National Natural Science Foundation of China (30300271)the State Key Basic Research and Development Plan of China (2004CCA02700)
文摘The Dahurian larch forest in northeast China is important due to its vastness and location within a transitional zone from boreal to temperate and at the southern distribution edge of the vast Siberian larch forest. The continuous carbon fluxes were measured from May 2004 to April 2005 in the Dahurian larch forest in Northeast China using an eddy covariance method. The results showed that the ecosystem released carbon in the dormant season from mid-October 2004 to April 2005, while it assimilated CO2 from the atmosphere in the growing season from May to September 2004. The net carbon sequestration reached its peak of 112 g.m^-2.month ^-1 in June 2004 （simplified expression of g （carbon）.m^-2.month^-1） and then gradually decreased. Annually, the larch forest was a carbon sink that sequestered carbon of 146 g-m^-2.a^-1 （simplified expression of g （carbon）.m^-2.a^-1） during the measurements. The photosynthetic process of the larch forest ecosystem was largely affected by the vapor pressure deficit （VPD） and temperature. Under humid conditions （VPD 〈 1.0 kPa）, the gross ecosystem production （GEP） increased with increasing temperature. But the net ecosystem production （NEP） showed almost no change with increasing temperature because the increment of GEP was counterbalanced by that of the ecosystem respiration. Under a dry environment （VPD 〉 1.0 kPa）, the GEP decreased with the increasing VPD at a rate of 3.0 μmol.m^-2.s^-1kPa -1 and the ecosystem respiration was also enhanced simultaneously due to the increase of air temperature, which was linearly correlated with the VPD. As a result, the net ecosystem carbon sequestration rapidly decreased with the increasing VPD at a rate of 5.2 μmol.m^-2.s-1.kPa^-1. Under humid conditions （VPD 〈 1.0 kPa）, both the GEP and NEP were obviously restricted by the low air temperature but were insensitive to the high temperature because the observed high temperature value comes within the category of the optimum range.
基金supported by the Natural Science Foundation of Jiangsu Province,China(BK20220017)the Innovation Development Project of China Meteorological Administration(CXFZ2023J073)+1 种基金the Key Research and Development Program of Anhui Province,China(2022M07020003)the Graduate Student Practice and Innovation Program of Jiangsu Province,China(SJCX22_0374)。
文摘To understand the CH_(4) flux variations and their climatic drivers in the rice-wheat agroecosystem in the Huai River Basin of China,the CH_(4) flux was observed by using open-path eddy covariance at a typical rice-wheat rotation system in Anhui Province,China from November 2019 to October 2021.The variations and their drivers were then analyzed with the Akaike information criterion method.CH_(4) flux showed distinct diurnal variations with single peaks during 9:00-13:00 local time.The highest peak was 2.15μg m^(-2)s^(-1)which occurred at 11:00 in the vegetative growth stage in the rice growing season(RGS).CH_(4) flux also showed significant seasonal variations.The average CH_(4)flux in the vegetative growth stage in the RGS(193.8±74.2 mg m^(-2)d^(-1))was the highest among all growth stages.The annual total CH_(4) flux in the non-rice growing season(3.2 g m^(-2))was relatively small compared to that in the RGS(23.9 g m^(-2)).CH_(4) flux increased significantly with increase in air temperature,soil temperature,and soil water content in both the RGS and the non-RGS,while it decreased significantly with increase in vapor pressure deficit in the RGS.This study provided a comprehensive understanding of the CH_(4) flux and its drivers in the rice-wheat rotation agroecosystem in the Huai River Basin of China.In addition,our findings will be helpful for the validation and adjustment of the CH_(4) models in this region.
基金supported by the National Natural Science Foundation of China(NSFC)(Nos.61335005,61325023,and 61401378)
文摘A flexible polarization demultiplexing method based on an adaptive Kalman filter（AKF） is proposed in which the process noise covariance has been estimated adaptively. The proposed method may significantly improve the adaptive capability of an extended Kalman filter（EKF） by adaptively estimating the unknown process noise covariance. Compared to the conventional EKF, the proposed method can avoid the tedious and time consuming parameter-by-parameter tuning operations. The effectiveness of this method is confirmed experimentally in 128 Gb/s 16 QAM polarization-division-multiplexing（PDM） coherent optical transmission systems. The results illustrate that our proposed AKF has a better tracking accuracy and a faster convergence（about 4 times quicker）compared to a conventional algorithm with optimal process noise covariance.
基金supported by the National Natural Science Foundation of China(Grant Nos.41030106,41021004)the National Basic Research Program of China(Grant No.2010CB951801)
文摘Measurement of turbulence fluxes were performed over the Erhai Lake using eddy covariance(EC) method.Basic physical parameters in the lake-air interaction processes,such as surface albedo of the lake,aerodynamic roughness length,bulk transfer coefficients,etc.,were investigated using the EC data in 2012.The characteristics of turbulence fluxes over the lake including momentum flux,sensible heat flux,latent heat flux,and CO2 flux,and their controlling factors were analyzed.The total annual evaporation of the lake was also estimated based on the artificial neural network(ANN) gap-filling technique.Results showed that the total annual evaporation in 2012 was 1165 ± 15 mm,which was larger than the annual precipitation(818 mm).Local circulation between the lake and the surrounding land was found to be significant throughout the year due to the land-lake breeze or the mountain-valley breeze in this area.The prevailing winds of southeasterly and northwesterly were observed throughout the year.The sensible heat flux over this plateau lake usually had a few tens of W m-2,and generally became negative in the afternoon,indicating that heat was transferred from the lake to the atmosphere.The sensible heat flux was governed by the lake-air temperature difference and had its maximum in the early morning.The diurnal variation of the latent heat flux was controlled by vapor pressure deficit with a peak in the afternoon.The latent heat flux was dominant in the partition of available energy in daytime over this lake.The lake acted as a weak CO2 source to the atmosphere except for the midday of summer.Seasonal variations of surface albedo over the lake were related to the solar elevation angle and opacity of the water.Furthermore,compared with the observation data,the surface albedo estimated by CLM4-LISSS model was underestimated in winter and overestimated in summer.
基金supported by the National Basic Research Program of China (Grant Nos. 2010CB951801 and 2006CB400500)
文摘Here we report a multiyear study on the surface roughness length and bulk transfer coefficients over the degraded grassland and cropland surfaces in a semiarid area of China. Eddy covariance measurement and the meteorological profile observation data were used to analyze characteristics of these parameters on the diurnal, seasonal, and annual scales. Significant seasonal and annual variations of the aerodynamic roughness length are observed over the two surfaces. A large variation of kB-1 is measured during the day. Both kB-1 and the bulk transfer coefficients exhibit significant seasonal and annual variations. During the growing season (May to October), average Cd and Ch are 3.1×10-3 and 2.5×10-3 over the degrade grassland surface, and 4.7×10-3 and 3.1×10-3 over the cropland surface respectively. During the non-growing season, average Cd and Ch are 2.3×10-3 and 2.0×10-3 over the degrade grassland surface, and 2.9×10-3 and 2.2×10-3 over the cropland surface respectively.
基金We would like to thank the Research Station of Changbai Mountain Forest Ecosystem,Chinese Academy of Sciences.This work was supported by the Na-tional Key Basic Research Development Program of China(Grant No.2002CB412502)the National Natural Science Foundation of China(Grant No.30370293)+1 种基金Knowledge Innovation Project of Chinese Academy of Sciences(Grant No.KZCX1-SW-01-01)the Frontier Project of Insti-tute of Applied Ecology,Chinese Academy of Sciences.
文摘Based on the light-photosynthesis response measurement at leaf level,combined with over-and under-canopy eddy covariance measurements,research on photosynthetic characteristics of single trees and forest canopy was conducted.The relationship between light intensity and photo-synthetic rates for leaves and canopy can be well fitted by a non-rectangular hyperbola model.Mongolian oak presented a high light compensation point,Lcp(28μmol·m-2·s-1),a light saturation point Lsp(>1800μmol·m-2·s-1),and a maximal net photosynthetic rate Pmax(9.96μmol·m-2·s-1),which suggest that it is a typical heliophilous plant.Mono maple presented the highest apparent quantum efficiencyα(0.066)but the lowest,Lcp(16μmol·m-2·s-1),Lsp(=800μmol·m-2·s-1),and Pmax(4.51μmol·m-2·s-1),which suggest that it is heliophilous plant.Korean pine showed the lowestαvalue but a higher Pmax,which suggest that it is a semi-heliophilous plant.At the canopy level,the values of both or and Pmax approached the upper limit of reported values in temperate forests,while Lcp was within the lower limit.Canopy photosynthetic characteristics were well consistent with those of leaves.Both showed a high ability to photosynthesize.However,environmental stresses,especially high vapor pressure deficits,could significantly reduce the photosynthetic ability of leaves and canopy.
基金This work was supported by the National Key Basic Research Development Program of China(Grant No.2002CB412502)the National Natural Science Foundation of China(Grant No.30370293)+1 种基金the Knowledge Innovation Project of the Chinese Academy of Sciences(Grant No.KZCX1-SW-01-0lA)the Frontier Project of Institute of Applied Ecology,Chidemy of Sciences.
文摘Based on analysis of mechanisms causing energy no-closure and nocturnal low fluxes issues for CO_(2) exchange studies by eddy covariance method,corrections were done with the raw data sets obtained from Changbai Mountains forest flux site,to evaluate the impacts of sonic anemometer tilt,frequency response limitations and advection on estimation of CO_(2) exchange,respectively.The results show that the planar fit coordinate transforming method is superior to the streamline coordinate transforming method in tilt correction.The latter could cause a systematical underestimation of eddy fluxes relating with the angle of sensor and terrain tilt.The underestimation of CO_(2) and energy fluxes for frequency response limitations average 3.0%and 2.0%during daytime,respectively,which increase by 9.0%and 5.5%during nighttime,respectively.The corrections of frequency response limitations are closely related to atmospheric stability.The advection loss of CO_(2) fluxes is dominated by nocturnal vertical advection,which is at least 18%when the horizontal advection is neglected.It is suggested that more work be done to understand the characteristics of horizontal advection and turbulent eddies under a complexcircumstance.
基金The authors are much grateful to Dr.Shusen Wang for his help in preparation of the manuscript.This work was supported by the Knowledge Innovation Program of the Chinese Academy of Sciences(CAS)"Studyon Carbon Budget in Terrestrial and Marginal Sea Ecosys-tems of China"(Grant No.KZCM1-SW-01)the Na-tional Key Basic Research and Development Program of the Ministry of Science and Technology of the People's Repub-lic of China"Carbon Cycle and Driving Mechanism in Chi-nese Terrestrial Ecosystem(Grant No.2002CB412500)
文摘The results of eddy covariance observation system could represent the physical process at certain area of the surface.Thus point-to-area representativeness was of primary interest in flux observation.This research presents a preliminary study for flux observation at ChinaFLUX sites by the use of observation data and Flux Source Area Model(FSAM).Results show that the footprint expands and is further away from flux tower when atmosphere becomes more stable,the observation height increases,or the surfaces become smoother.This suggests that the area represented by the flux observation becomes larger.The distances from the reference point to the maximum point Smax and the minimum point x1 of source weight function(Dmax and Dmin,respectively)can be influenced by atmosphere stability which becomes longer when atmosphere is more stable.For more rough surfaces and lower observation point Dmax and Dmin become shorter.This research gives the footprint at level P=90%at ChinaFLUX sites at different atmosphere stability.The preliminary results of spatial representiveness at ChinaFLUX sites were given based on the dominant wind direction and footprint response to various factors.The study also provides some theoretical basis for data quality control and evaluating data uncertainty.
基金supported by the National Basic Research Program of China (Grant Nos.2010CB951801and 2006CB400501)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (Grant No.41021004)
文摘Based on the carbon fluxes measured over the grassland ecosystems in Inner Mongolia （UG79 site）, Loess Plateau （SACOL site）, and Tongyu, Jilin Province （TY site） in the semiarid areas from 2007 to 2008 with the eddy covariance method, we have investigated the carbon exchange processes over semiarid grassland ecosystem and its main affecting environmental variables. The precipitations at UG79 and TY sites in 2007 were below the historical average, especially for TY site, which was 50% be- low the historical average annual precipitation. The precipitation in SACOL site was close to average in 2007 but below average in 2008. The variation of monthly diurnal average NEE showed that the diurnal mean NEE decreased in the order of TY site, UG79 site, and SACOL site. However, a longer net carbon uptake period was observed at SACOL site. The diurnal course of NEE at UG79 site was similar between 2007 and 2008. The diurnal average NEE remained large during July and August in growing sea- son （May to September） at UG79 site, with maximum values approaching 0.08 mg C m^-2 s^-1 in August of 2008. The diurnal av- erage NEE of 2007 was larger than 2008 at SACOL site, with maximum values of 0.07 mg C m^-2 sq in September of 2007. A shorter carbon uptake period was recorded in 2007 at TY site, lasting from July to August. A larger diurnal average NEE oc- curred in 2008 at TY site, with maximum values of 0.12 mg C m^-2 s^-1. The ecosystem respirations of three sites were controlled by both soil temperature and soil volumetric water content （at a depth of 5 cm below the land surface）. Both UG79 site and SACOL site acted as a carbon sink during the growing periods of 2007 and 2008. Annual NEE in the growing seasons of 2007 and 2008 ranged from -68 to -50 g C m^-2 at UG79 site and from -109 to -55 g C m^-2at SACOL site. Alternation between car- bon source and carbon sink was found at TY site, with respective values of annual NEE in the growing seasons of 0.32 g C m^-2 and -73 g C m^-2 in 2007 and 2008. The magnitude and duration of carbon uptake depended mainly on the amount and timing of precipitation and the timing of the first effective rainfall during the growing season in semiarid grassland ecosystems.
基金National Natural Science Foundation of China Grant 40275004City University of Hong Kong Grant 8780046+1 种基金the City University of Hong Kong Strategic Research Grant 7001038State Key Laboratory of Atmospheric Boundary Layer Physics and Atmospheric Chemistry
文摘Mainly.three methods have been developed to calculate turbulence heat flux.They are eddy covariance method,Bowen ratio/energy balance method and aerodynamic method.In this paper, all the three methods have been used to calculate sensible heat flux,latent heat flux and imbalance energy near the surface with the experiment data of EBEX-2000.Then comparisons of the three methods and some possible explanations of the surface imbalance energy are given.
