华北平原冬麦田土壤CH₄的吸收特征研究          下载免费PDF全文

张雪松  申双和  李俊  于强 《大气科学学报》2006,29(2):181-188

利用静态箱/气相色谱(GC)法,对华北平原冬小麦拔节-成熟期间麦田土壤CH₄气体通量进行了测定,得出华北平原典型冬麦田土壤是大气CH₄的弱吸收汇。试验期间土壤CH₄通量存在明显的季节变化和日变化,麦田拔节-成熟期间土壤CH₄通量日平均值为-18.3μg·m^-2·h^-1,波动范围为-4.3-24.4μg·m^-2·h^-1;在土壤CH₄通量的日变化中,观测到麦田土壤在午间和夜间都有一个吸收峰,峰值出现的时间因生育期不同而有所不同。试验期间CH₄通量日平均值与土壤温度关系不明显,而与土壤水分呈负相关(α=0.01);日变化中土壤CH₄通量与地表温度的相关性较差,而与5cm地温相关密切。麦田拔节-成熟期间土壤CH₄通量日平均值随NH4+-N施用量的增加呈递减规律,农田秸秆还田后不利于土壤对CH₄的吸收。  相似文献   

2014—2019年北京和南京地区PM_2.5和臭氧质量浓度相关性研究     

孙金金  黄琳  龚康佳  王雪颖  李婧祎  秦墨梅  于兴娜  胡建林 《南京气象学院学报》2020,12(6):656-664

自2014年以来,中国细颗粒物（PM_2.5）浓度大幅度下降,但臭氧（O₃）浓度逐年缓慢上升,厘清PM_2.5和O₃（P-O）相关性尤为关键.在本研究中,2014—2019年北京和南京PM_2.5年均质量浓度下降幅度分别为-6.86和-6.15 μg·m^-3·a^-1;而日最大8小时平均O₃质量浓度（MDA8 O₃）年均增长幅度为1.50和1.75 μg·m^-3·a^-1.研究期间,北京地区MDA8 O₃质量浓度小于100 μg·m^-3,P-O呈负相关;而当质量浓度大于100 μg·m^-3时,P-O为正相关.通过Pearson相关系数研究P-O两者相关性.在两个城市每月相关性分析中,在每日时间尺度5—9月为强的正相关;而小时时间尺度11月至次年2月趋于负相关.在北京,P-O每月和季节相关性变化大于南京.在日变化中,夏季在16时为强的正相关,春秋两季在13—17时为弱的正相关,而在春、秋和冬季8时,却为强的负相关.  相似文献   

2007和2008年夏季北京奥运馆大气PM₁₀与PM_2.5质量浓度变化特征   总被引：6，自引：1，他引：5  

李雪  刘子锐  任希岩  李昕  王跃思 《大气科学学报》2012,35(2):197-204

为了监测北京奥运主场馆附近大气颗粒物的污染状况以及评估奥运污染源减排措施对北京大气颗粒物质量浓度变化的影响,利用颗粒物在线监测仪器TEOM于2007年和2008年夏季,在奥运主场馆附近的中国科学院遥感应用研究所办公楼楼顶对大气颗粒物PM₁₀和PM_2.5进行了连续同步观测。结果表明,2007年夏季监测点附近大气PM₁₀与PM_2.5质量浓度的平均值分别为153.9和71.2μg·m^-3,而2008年夏季PM₁₀与PM_2.5质量浓度的平均值分别为85.2和52.8μg·m^-3。与奥运前一年同时段相比,奥运时段大气PM₁₀和PM_2.5的质量浓度分别下降44.5%和25.1%。对比分析奥运前后的2次典型污染过程发现,空气相对湿度的增加和偏南气流输送的共同影响易造成大气颗粒物的累积增长,而降雨的湿清除作用和偏北气流则会使大气颗粒物浓度迅速降低。在相近的气象条件下,奥运前后的污染过程中,大气细粒子的日均增长速率分别为25.1和13.9μg·m^-3·d^-1,而大气粗粒子的日均增长速率分别为20.8和2.2μg·m^-3·d^-1,奥运时段污染累积过程中大气粗、细粒子的增长速率分别显著低于和略低于奥运前同时段污染过程中颗粒物的增长速率。污染源减排措施的实施是奥运期间大气颗粒物质量浓度降低的主要原因,从控制效果来看,奥运期间实施的污染源减排措施对大气粗粒子的控制效果明显好于大气细粒子。  相似文献   

2016年冬季南京地区大气污染特征的观测分析     

崔金梦  王体健  高丽波  曹云擎  王勤耕 《气象科学》2020,40(4):427-437

基于2016年11月24日—12月23日南京市草场门站、鼓楼站和仙林站的强化试验观测资料,分析了城市和郊区主要大气污染物的时空变化特征及其与气象要素的相互关系。研究发现：观测期间南京PM_2.5、PM₁₀、NO₂、O₃、CO、SO₂月均质量浓度分别为52.84~84.34 μg·m^-3、88.36~120.34 μg·m^-3、49.98~51.66 μg·m^-3、24.85~50.57 μg·m^-3、0.99~1.2 mg·m^-3和22.1~26.48 μg·m^-3;近地面,城市大气污染物质量浓度高于郊区,其中城市O₃比郊区高61.0%;在城市地区,除NO₂和CO外,鼓楼站大气污染物质量浓度高于草场门站,其中鼓楼站PM_2.5比草场门站高42.7%;PM_2.5小时质量浓度最大为210.93 μg·m^-3,重污染过程出现时风速较低、温度较高,郊区PM₁₀、PM_2.5、NO₂质量浓度呈现高值时的最频风向为南风,O₃和SO₂质量浓度呈现高值时的最频风向分别为西风和西南风,所以郊区大气污染受城市输送影响。利用HYSPLIT模式研究发现12月4—8日和16—20日的污染气团分别来自西部和北方地区,聚类分析发现12月影响南京市的污染气团45%来自西部地区且移动速度较快,55%来自北方地区且移动速度较慢。由此可见,南京市冬季出现的大气污染,其形成不仅与本地排放和局地气象条件有关,而且西部和北方地区的远距离输送也会造成影响。  相似文献   

山西省城市大气CO₂本底筛分对比及特征分析          下载免费PDF全文

王淑敏  张逢生  贺洁颖  朱凌云  高兴艾  裴坤宁 《气象科学》2023,43(5):680-688

基于典型城市站太原站2018年3月—2019年2月的大气CO₂在线观测资料，利用筛分法（Meteorological filtering method，MET）和黑碳示踪法（Black Carbon tracer，BC）进行本底/非本底的筛分，得到了本底浓度的变化特征。结果表明，太原大气CO₂浓度季均值冬季最高，夏季最低；不同季节呈"单峰型"日变化特征，日振幅均在26.0×10^-6以上；4个季节CO₂浓度与地面风速存在显著负相关关系；CO₂浓度抬升区域主要受当地工业布局的影响，最大抬升幅度在秋季达17.4×10^-6；使用气象筛分法（MET）得到年均本底浓度为（431.4±19.9）×10^-6，人为排放等对其影响为23.5×10^-6，年振幅比同纬度其它本底站大，为34.5×10^-6；黑碳示踪法（BC）得到冬季季均本底浓度为（445.0±22.9）×10^-6，比MET筛分法得到的季均值高0.8×10^-6，两种筛分法得到的CO₂浓度变化趋势一致。  相似文献   

城市下垫面影响空气污染的机制分析          下载免费PDF全文

羊腾跃  刘红年  王学远  胡非 《气象科学》2021,41(6):780-790

本文采用RBLM-chem模式,利用杭州市高分辨率城市建筑等资料,定量分析城市动力效应、热力效应以及城市植被、人为热对SO₂、NO₂、O₃、PM_2.5等主要污染物浓度的影响。结果表明,城市化过程使得大部分城区温度上升约1℃,相对湿度下降约6%,风速下降约0.8 m·s^-1,湍流动能增强约0.03 m²·s^-2。城市动力效应主要通过降低城市风速,使得城区污染物浓度升高,SO₂浓度有近5 μg·m^-3的上升,PM_2.5、O₃浓度也有近15 μg·m^-3的上升。城市热力效应主要通过热岛环流使城区污染物向上输送,令地面污染物浓度降低,在城市大部分区域PM_2.5都有大约10 μg·m^-3的浓度下降。城市动力效应大于热力效应,城市的总体作用是使污染物浓度升高。城市下垫面使污染物浓度上升的另外一个机制是代替了自然有植被的下垫面,使污染物干沉降速度下降,但这一作用小于动力学效应。另一方面,人为热对城市主要污染物浓度都起着减小的作用,其中SO₂、NO₂、O₃、PM_2.5浓度降幅分别在2.5、3.0、6.0、10.0 μg·m^-3左右。城市植被可以显著增加污染物干沉降速度,使主要污染物SO₂、NO₂、O₃和PM_2.5的干沉降速度分别上升0.1、0.1、0.03、0.06 m·s^-1左右,相应地使上述污染物浓度分别下降2.5、6.0、4.0、6.0 μg·m^-3左右。  相似文献   

基于LAS观测的城镇感热通量时空特征及影响因素          下载免费PDF全文

刘寿东  王璐瑶  胡凝  王咏薇  王亮  赵翔 《大气科学学报》2023,46(4):630-640

利用2018年4月—2019年4月南京盘城大孔径闪烁仪(Large Aperture Scintillometer,LAS)观测数据,分析了城镇感热通量的时空变化特征及影响因素。结果表明:1)南京城镇感热通量呈单峰型日变化特征,白天明显大于夜间,且白天晴天明显大于阴天,夜间晴天略小于阴天,晴、阴天小时感热通量年平均分别在2.25～200.53 W·m^-2、13.10～132.52 W·m^-2波动。2)城镇感热通量夏季明显大于冬季,8月昼、夜分别为112.19、23.54 W·m^-2,2月昼、夜分别为35.57、11.57 W·m^-2。3)晴天白天条件下,不同风向(通量贡献源区)城镇感热通量存在显著差异,即随着不透水层占比的增加,净辐射分配到感热通量的比例明显提高,当占比大于60％时提高趋势不明显。4)以莫宁-奥布霍夫长度判断大气稳定度为标准,C²_n法在计算感热通量的5种大气稳定度判断方法中的误判率较低且数据源于LAS,是比较适宜城镇夜间大气稳定度的判断方法。5)在影响城镇感热通量的地表参数中,有效高度变化的影响最大,风速变化的影响较大特别在秋冬季节更为明显,波文比变化对城镇感热通量的影响较小,温度、地表粗糙度和零平面位移变化的影响可忽略不计。  相似文献   

大气CO₂富集对根际NaCl盐渍的人参果植株干物质生产和水分利用的影响     

陈凯  胡国谦  KEUTGEN Norbert  KEUTGEN Ann  JANSSENS Mar  LENZ Fritz 《大气科学学报》2012,35(2):129-139

对单株砂培盆栽的半木质化枝条扦插生根的一月龄人生果(Solanum muricatum Ait.)栽培品种"Xotus",每周浇两次200mL NaCl质量浓度分别为0mg·L^-1和25mg·L^-1的Hoagland营养液处理2个月,第二个月在控制空气CO₂体积分数为(350±10)×10^-6、(700±10)×10^-6和(1050±10)×10^-6的植物生长箱内试验。结果表明,人参果植株干物质生产量和耗水量受根际NaCl盐渍而下降,又随大气CO₂升高而增加。根际NaCl盐渍能增大植株叶片蒸腾系数、根/冠比和干物质向枝干和根部分配的比例及积累量,降低根系吸收水分的效率和耗水量。升高大气CO₂能促进叶片发育及干物质向地上部其他器官和地下部组织分配,增加总叶面积、比叶干重和各种器官中干物质增长量,提高干物质生产率和水分利用率。根际经25mg·L^-1NaCl盐渍处理的植株,总干物质增长量和水分利用率相应下降50%～54%和24%～37%;与350×10^-6CO₂的处理的植株相比,700×10^-6及1050×10^-6CO₂的处理分别使这两项指标提高到79%～106%和61%～88%以及133%～189%和99%～142%。大气CO₂富集能改善受NaCl盐渍的植株干物质生产力、提高水分利用率。根际NaCl盐渍和大气CO₂富集对人参果植株干物质生产和水分利用有生物互作效应。它们的共同作用会促进植株干物质的增长及叶片中合成的干物质向其他器官分配,提高干物质生产率和水分利用率,同时减少总叶面积、枝条和根系干重、根系吸水效率、植株耗水量和叶片蒸腾系数。因此,全球大气CO₂富集将有利于该作物的干物质生产和水分利用。  相似文献   

东亚地区二氧化碳体积分数变化特征     

党小晨  张美根  朱彬 《南京气象学院学报》2012,4(1):40-46

利用2004年以来东亚地区10个本底观测站大气φ(CO₂)观测资料,分析了各站大气φ(CO₂)的变化特征及其各站之间的差异,讨论了下垫面特征、源汇作用等对φ(CO₂)变化的影响.结果表明:10个本底站大气月均φ(CO₂)有明显的季节变化,高值多出现在冬春等寒冷季节,而低值则多出现在6—9月,属于北半球的夏季;大气φ(CO₂)日变化趋势较为一致,15时(当地时间)前后达到全天最低,随后φ(CO₂)升高,并在日落后继续积累,至清晨7时(当地时间)前后达到全天最高,之后φ(CO₂)随着太阳辐射的增强而逐渐降低,且平均φ(CO₂)水平与下垫面植被量成反比,φ(CO₂)日变化的幅度与下垫面植被量成反比.作为全球基准站之一的瓦里关山站,2004—2008年φ(CO₂)年均值逐年增加,年增长率为2.28×10^-6/a.  相似文献   

福建三明市春季PM_2.5中有机碳、元素碳和水溶性离子特征分析     

程瑾  张青宁  张冰洁  周鲁宇  郑军 《南京气象学院学报》2016,8(3):239-246

2014年3月13日至4月20日在福建三明市利用PM_2.5中流量采样器采集大气中PM_2.5膜样品,测定了PM_2.5的质量浓度,并用热/光碳分析仪和离子色谱分析了其组分变化特征.结果表明,三明市观测期间PM_2.5的平均质量浓度为73.61±0.73 μg/m³,有机碳(OC)和元素碳(EC)的平均质量浓度分别为7.26±1.00和5.63±0.27 μg/m³,水溶性离子中SO₄^2-、NH₄⁺、NO₃^-和Na⁺的质量浓度分别为18.08±12.19、4.18±3.56、2.77±1.16和2.73±0.23 μg/m³,总和占总水溶性离子的87.76%.结合后向轨迹分析了福建三明市的污染物来源特征.该地区OC/EC的平均比值小于2,SOC(二次有机碳)生成量很少,主要以一次有机污染物为主,OC、EC与K⁺的相关性分析表明OC、EC与K⁺的来源相近,可以判断OC、EC绝大部分来源是生物质燃烧产生的污染物.在水溶性离子分析中,观测期间NO₃^-/SO₄^2-为0.159±0.02,表明三明市主要以固定源为主,机动车辆等移动源贡献较少.  相似文献   

Seasonal carbon dioxide balance and respiration of a high-arctic fen ecosystem in NE-Greenland   总被引：2，自引：0，他引：2  

C. Nordstroem  H. Soegaard  T. R. Christensen  T. Friborg  B. U. Hansen 《Theoretical and Applied Climatology》2001,70(1-4):149-166

Summary  Turbulent fluxes of CO₂ were continuously measured by eddy correlation for three months in 1997 over a gramineous fen in a high-arctic environment at Zackenberg (74°28′12″N, 20°34′23″W) in NE-Greenland. The measurements started on 1 June, when there was still a 1–2 m cover of dry snow, and ended 26 August at a time that corresponds to late autumn at this high-arctic site. During the 20-day period with snow cover, fluxes of CO₂ to the atmosphere were small, typically 0.005 mg CO₂ m⁻² s⁻¹ (0.41 g CO₂ m⁻² d⁻¹), wheres during the thawed period, the fluxes displayed a clear diurnal variation. During the snow-free period, before the onset of vegetation growth, fluxes of CO₂ to the atmosphere were typically 0.1 mg CO₂ m⁻² s⁻¹ in the afternoon, and daily sums reached values up to almost 9 g CO₂ m⁻² d⁻¹. After 4 July, downward fluxes of CO₂ increased, and on sunny days in the middle of the growing season, the net ecosystem exchange rates attained typical values of about −0.23 mg m⁻² s⁻¹ at midday and max values of daily sums of −12 g CO₂ m⁻² d⁻¹. Throughout the measured period the fen ecosystem acted as a net-sink of 130 g CO₂ m⁻². Modelling the ecosystem respiration during the season corresponded well with eddy correlation and chamber measurements. On the basis of the eddy correlation data and the predicted respiration effluxes, an estimate of the annual CO₂ balance the calender year 1997 was calculated to be a net-sink of 20 g CO₂ m⁻² yr⁻¹. Received October 6, 1999 Revised May 2, 2000  相似文献   

Net CO2 exchange of a subarctic mountain birch ecosystem     

M. Aurela  J.-P. Tuovinen  T. Laurila 《Theoretical and Applied Climatology》2001,70(1-4):135-148

Summary  Net ecosystem CO₂ exchange was measured over a mountain birch forest in northern Finland throughout the growing season. The maximal net CO₂ uptake rate of about − 0.5 mg(CO₂) m⁻² s⁻¹ was observed at the end of July. The highest nocturnal respiration rates in early August were 0.2 mg(CO₂) m⁻² s⁻¹. The daily CO₂ balances during the time of maximal photosynthesis were about −15 g(CO₂) m⁻² d⁻¹. The mountain birch forest acted as a net sink of CO₂ from 30 June to 28 August. During that period the net CO₂ balance was −448 g(CO₂)m⁻². The interannual representativeness of the observed balances was studied using a simplified daily balance model, with daily mean global radiation and air temperature as the input parameters. The year-to-year variation in the phenological development was parameterised as a function of the cumulative effective temperature sum. The daily balance model was used for estimating the variability in the seasonal CO₂ balances due to the timing of spring and meteorological factors. The sink term of CO₂ in 1996 was lower than the 15-year mean, mainly due to the relatively late emergence of the leaves. Received October 11, 1999 Revised April 25, 2000  相似文献   

Temperature and snow-melt controls on interannual variability in carbon exchange in the high Arctic     

L. Groendahl  T. Friborg  H. Soegaard 《Theoretical and Applied Climatology》2007,88(1-2):111-125

Summary Net Ecosystem CO₂ Exchange (NEE) was studied during the summer season (June–August) at a high Arctic heath ecosystem for 5 years in Zackenberg, NE Greenland. Integrated over the 80 day summer season, the heath is presently a sink ranging from −1.4 g C m⁻² in 1997 to −23.3 g C m⁻² in 2003. The results indicate that photosynthesis might be more variable than ecosystem respiration on the seasonal timescale. The years focused on in this paper differ climatically, which is reflected in the measured fluxes. The environmental conditions during the five years strongly indicated that time of snow-melt and air temperature during the growing season are closely related to the interannual variation in the measured fluxes of CO₂ at the heath. Our estimates suggest that net ecosystem CO₂ uptake is enhanced by 0.16 g C m⁻² per increase in growing degree-days during the period of growth. This study emphasises that increased summer time air temperatures are favourable for this particular ecosystem in terms of carbon accumulation.  相似文献   

Gap Filling and Quality Assessment of CO2 and Water Vapour Fluxes above an Urban Area with Radial Basis Function Neural Networks     

A. Schmidt  T. Wrzesinsky  O. Klemm 《Boundary-Layer Meteorology》2008,126(3):389-413

Vertical turbulent fluxes of water vapour, carbon dioxide, and sensible heat were measured from 16 August to the 28 September 2006 near the city centre of Münster in north-west Germany. In comparison to results of measurements above homogeneous ecosystem sites, the CO₂ fluxes above the urban investigation area showed more peaks and higher variances during the course of a day, probably caused by traffic and other varying, anthropogenic sources. The main goal of this study is the introduction and establishment of a new gap filling procedure using radial basis function (RBF) neural networks, which is also applicable under complex environmental conditions. We applied adapted RBF neural networks within a combined modular expert system of neural networks as an innovative approach to fill data gaps in micrometeorological flux time series. We found that RBF networks are superior to multi-layer perceptron (MLP) neural networks in the reproduction of the highly variable turbulent fluxes. In addition, we enhanced the methodology in the field of quality assessment for eddy covariance data. An RBF neural network mapping system was used to identify conditions of a turbulence regime that allows reliable quantification of turbulent fluxes through finding an acceptable minimum of the friction velocity. For the data analysed in this study, the minimum acceptable friction velocity was found to be 0.15 m s⁻¹. The obtained CO₂ fluxes, measured on a tower at 65 m a.g.l., reached average values of 12 μmol m⁻² s⁻¹ and fell to nighttime minimum values of 3 μmol m ⁻² s⁻¹. Mean daily CO₂ emissions of 21 g CO₂ m⁻²d ⁻¹ were obtained during our 6-week experiment. Hence, the city centre of Münster appeared to be a significant source of CO₂. The half-hourly average values of water vapour fluxes ranged between 0.062 and 0.989 mmol m⁻² s⁻¹and showed lower variances than the simultaneously measured fluxes of CO₂.  相似文献   

Eddy correlation measurements of CO2, latent heat,and sensible heat fluxes over a crop surface   总被引：14，自引：0，他引：14  

Dean E. Anderson  Shashi B. Verma  Norman J. Rosenberg 《Boundary-Layer Meteorology》1984,29(3):263-272

Eddy correlation equipment was used to measure mass and energy fluxes over a soybean crop. A rapid response CO₂ sensor, a drag anemometer, a Lyman-alpha hygrometer and a fine wire thermocouple were used to sense the fluctuating quantities.Diurnal fluxes of sensible heat, latent heat and CO₂ were calculated from these data. Energy budget closure was obtained by summing the sensible and latent heat fluxes determined by eddy correlation which balanced the sum of net radiation and soil heat flux. Peak daytime CO₂ fluxes were near 1.0 mg m^–2 (ground area) s^–1.The eddy correlation technique was also employed in this study to measure nocturnal CO₂ fluxes caused by respiration from plants, soil, and roots. These CO₂ fluxes ranged from - 0.1 to - 0.25 mg m^–2s^–1.From the data collected over mature soybeans, a relationship between CO₂ flux and photosynthetically active radiation (PAR) was developed. The crop did not appear to be light-saturated at PAR flux densities < 1800 Ei m^–2 s^–1. The light compensation point was found to be about 160 Ei m^–2 s^–1.Published as Paper No. 7402, Journal Series, Nebraska Agricultural Experiment Station. The work reported here was conducted under Nebraska Agricultural Experiment Station Project 27-003 and Regional Research Project 11–33.Post-doctoral Research Associate, Professor and Professor, respectively. Center for Agricultural Meteorology and Climatology, Institute of Agriculture and Natural Resources, University of Nebraska, Lincoln, NE 68583-0728.  相似文献   

Effects of an Urban Park and Residential Area on the Atmospheric CO₂ Concentration and Flux in Seoul, Korea   总被引：1，自引：0，他引：1  

Moon-Soo PARK  Seung Jin JOO  Chang Seok LEE 《大气科学进展》2013,30(2):503-514

The CO₂ concentrations and fluxes over an urban forest site (Namsan) and an urban residential region (Boramae) in Seoul, Korea, during the non-growing season (2–4 March 2011), the growing season (10–12 June 2011), and the late-growing season (22–24 September 2011) were analyzed. The CO₂ concentrations of two sites showed nearly the same diurnal variation, with a maximum value occurring during the night and a minimum value occurring during daytime, as well as the same seasonal variation, with a maximum value during the non-growing season (early spring) and a minimum value during the growing season (summer). The CO₂ flux over the urban forest did not show any typical diurnal variation during the non-growing season, but did show diurnal variation with a small positive value during the night and a large negative value during daytime in the growing and late-growing seasons due to photosynthesis in the urban forest. The CO₂ flux over the urban residential region showed a positive daily mean value for all periods, with large values during the non-growing season and small values during the growing season, and it also showed diurnal variation with two maxima at 0600–1000 LST and 1800–2400 LST, and two minima at 0300-0600 LST and 1100-1500 LST, and was strongly correlated with the use of liquefied natural gas for cooking and heating by surrounding houses.  相似文献   

The Influence of Advection on the Short Term CO 2 -Budget in and Above a Forest Canopy     

C. Feigenwinter  C. Bernhofer  R. Vogt 《Boundary-Layer Meteorology》2004,113(2):201-224

An experimental micrometeorological set-up was established at the CARBOEURO-FLUX site in Tharandt, Germany, to measure all relevant variables for the calculation of the vertical and horizontal advective fluxes of carbon dioxide. The set-up includes two auxiliary towers to measure horizontal and vertical CO₂ and H₂O gradients through the canopy, and to make ultrasonic wind measurements in the trunk space. In combination with the long-term flux tower an approximately even-sided prism with a typical side-length of 50 m was established. It is shown that under stable (nighttime) conditions the mean advective fluxes have magnitudes on the same order as the daily eddy covariance (EC) flux, which implies that they play a significant, but not yet fully understood, role in the carbon budget equation. The two advective fluxes are opposite and seem to cancel each other at night (at least for these measurements). During the day, vertical advection tends to zero, while horizontal advection is still present implying a flow of CO₂ out of the control volume. From our measurements, a mean daily gain of 2.2 gC m^–2 d^–1 for the horizontal advection and a mean daily loss of 2.5 gC m^–2d^–1 for the vertical advection is calculated for a period of 20 days. However the large scatter of the advective fluxes has to be further investigated. It is not clear yet whether the large variability is natural or due to measurement errors and conceptual deficiencies of the experiment. Similar results are found in the few comparable studies.  相似文献   

THE ENERGY BUDGETS UNDER DIFFERENT SYNOPTIC CONDITIONS OVER HUAIHE RIVER BASIN DURING HUBEX FIELD OBSERVATION PERIODS IN 1999^*     

HU Guoquan  DING Yihui 《Acta Meteorologica Sinica》2002,16(3):293-308

In different synoptic conditions and at different time scales,the analysis of the energy budgets by Bowen Ratio Method and Bulk Schemes over Huaihe River Basin during the field observation periods of HUBEX in 1999 shows that,(1) the averaged latent heat flux is an order of magnitude more than the averaged sensible heat flux during the observation period:(2) the variation of totalcloud amount is out of phase with the terms of energy budgets except for the downward longwave radiation which maybe is related to the cloud's height and class:(3) the values of sensible and latent heat fluxes are small during rain episodes,but thereafter,the values become high and then up to maximum.It is similar to the other terms of the energy budgets except for the downward longwave radiation.The diurnal variation of energy budgets indicates that the daytime precipitation exerts great influence to the energy budgets,but the nighttime precipitation makes little influence;(4) the variation of the latent heat flux is in phase with the evaporation,which indicates that the latent heat flux calculated by bulk schemes is reliable:(5) the means of the sensible and latent heat flux and momentum flux by bulk schemes for the time period from May to August are,respectively,30.71W/m².116.81W/m².2.86×10^-2N/m² in 1998 and 30.28W/m²,107.35W/m²,2.74×10^-2N/m² in 1999.The values of these two years are similar.During summer in 1999 the magnitude and activity of sensible heat flux are strongest in June and those of the latent heat flux are in August.  相似文献   

The diurnal cycle of surface air temperature in simulated present and doubled CO2 climates     

I. G. Watterson 《Climate Dynamics》1997,13(7-8):533-545

 The diurnal range of surface air temperature (rT _a ) simulated for present and doubled CO₂ climates by the CSIRO9 GCM is analysed. Based on mean diurnal cycles of temperature and surface heat fluxes, a theory for understanding the results is developed. The cycles are described as the response to a diurnal forcing which is represented well by the diurnal mean flux of net shortwave radiation at the surface (SW) minus the evaporative (E) and sensible (H) fluxes. The response is modified by heat absorbed by the ground, and by the cycle in downward longwave (LW) radiation, but these effects are nearly proportional to the range in surface temperature. Thus in seasonal means, rT _a is approximately given by SW–E–H divided by 6 W m^-2/^°C. A multiple regression model for (rT _a ) is developed, based on quantities known to influence SW, E and H, and applied to both spatial variation in seasonal means, and day-to-day variation at a range of locations. In both cases, rT _a is shown to be influenced by cloud cover, snow extent and wind speed. It is influenced by soil moisture, although this effect is closely tied to that of cloud. In seasonal means rT _a is also well correlated with precipitable water, apparently because of the latter’s influence on E+H. The regression model describes well the spatial variation in the doubled CO₂ change in rT _a . The annual mean change in rT _a over land on doubling CO₂ was −0.36 ^°C, partly because of a decrease in the mean diurnal forcing (as defined in the theory), but also apparently because of the effect of nonlinearity in T _s of the upward longwave emission. A diagnostic radiation calculation indicates that the CO₂ and water vapour provide a small increase in rT _a through the downward LW response, which partially counters a decrease due to a reduction of SW by the gases. Received: 8 November 1995 / Accepted: 3 January 1997  相似文献