随机误差和系统误差对估算可能蒸散量的影响

1 引言彭曼(Penman,1948)建立的蒸发方程,起初用来估计开敞水面的蒸发。该方程可表示为: E_0=[(△R_n) (γE_a)]/(△ γ) (1)式中E_0为开敞水面的蒸发(mm d~(-1));R_n为净辐射(mm/天)。若不直接观测净辐射,则可用下式估计:     

最大蒸发量的计算、分析及其应用

本文利用潘曼(Penman)公式E_0=(ΔH rE_a)/(Δ r),计算了宁夏各地自然蒸发量E_r值,分析了E_r的时空分布特征;以E_r/r的比值(干燥指数)作为划分宁夏农业气候区域的指标,并根据E_r=L_iE_0的关系式,订正了宁夏地区春、夏、秋各季的转换系数K_i值;以计算出的农作物各生育期内自由水面蒸发量E_0值和实测田间蒸发量′fc的比例系数(′fc/E_0),作为土壤-植物-近地表层这个系统的水份状况的重要指标,鉴定出了宁夏灌区小麦、水稻、小糜子等主要作物生育期的蒸发系数j_t值和耗水量。用水分平衡方程式,求出了作物灌溉量和生育末期土壤水分储水量,为研究宁夏农业气候区划及建立农作物水分平衡预报,提供了依据。     

论陆面蒸发的计算

本文从蒸发E随降水的改变率E/r是剩余蒸发力E_0—E和降水r的函数,即E/r=f(E_0-E,r),而蒸发随蒸发力的改变率E/E_0是剩余水量,r—E和蒸发力E_0的函数,即E/E_0=φ(r-E,E_0)的考虑出发,利用量纲分析和微分方程理论确定了函数f和Φ的表述式,并由此得到根据蒸发力和降水计算陆面蒸发的公式。计算结果非常令人满意。     

雨水耗热与蒸发的计算

作者考虑到雨水耗热,得到如下计算日蒸发量的公式 E=[ΔR_n 0.5E_a(1 Id/190)]/[Δ_0.5(1 Id/190)],式中Id是日降雨量(毫米)。在降雨大的情况下,用此式计算的结果看来比Penman公式要好。     

东江流域蒸散发量变化趋势及其原因分析

将广东境内东江流域3个国家基准站的水皿蒸发量Epan观测资料与Penman公式估算蒸发能力E0的结果进行对比,得到两者平均相对误差为16.2%。分析了东江流域1956～2006年4个基准站Epan、E0、由FAO-56 Penman-Monteith公式估算蒸散量ET0及气象观测资料的50年变化趋势,其中温度t呈上升趋势,相对湿度μ、日照时数n、风速v呈下降趋势,降水无显著趋势。分析结果表明寻乌站(无Epan资料)存在较明显的"蒸发悖论"现象;惠阳站表现出一定"悖论"特点,连平、河源不存在"悖论"现象。进一步分析E0、ET0与各气象因子的关系知n和μ对E0、ET0的影响大于t和v,在出现"悖论"现象的2个站,n和μ的作用比没有"悖论"的两个站更明显,可见在东江地区n和μ的共同作用是"悖论"形成的关键。     

论陆面蒸发量的计算

在的著作中,根据基本假定形式x=∫_0~z(dz/((1-(z/z_0))~n)进行了陆面蒸发量的推算。但该式只有在极少数情况下能够进行积分,就是积分所取得的公式也是相当复杂,且仅当n=1及2时能取得z对于x和z_1的显函数。 本丈将的假定形式改成如下形式: x=∫_0~z(dz/(1-(z/z_0))~(1/n)) 上式在n为任何数值时都可以积分,且取得的公式非常简单。根据所得的公式曾计算了不同z值(当z_0=1时)和对应的x值,并利用这些计算的数据绘出了图1上的曲线(以实线表示),同时也将的曲线绘在图1上(以虚线表示)。两曲线比较的结果指出,当(x/z_0)<1.10时所有实线都位于虚线之下,当(x/z_0)>1.10时所有实线逐渐位于虚线之上,且随着(x/z_0)的增加,两组曲钱位置相距愈远。     

中央渔场三——五天无大风时段的预报

一、中央渔场无大风实况记录的处理: 中央渔场(23—37°N,119—132°E范围)无观测资料,如何判断该地区有无大风?我们知道,在高压或高压楔控制的地区,水平气压梯度Δp/Δn是很小的,由地转风公式     

东亚地区对流层人为硫酸盐辐射强迫及其温度响应

利用区域气候模式对东亚地区人为硫酸盐的直接辐射强迫及其温度响应进行了数值研究.结果表明:(1)人为硫酸盐直接辐射强迫具有明显的季节变化和地理分布特征,辐射强迫的这种变化特征不仅强烈地依赖于硫酸盐柱含量的季节变化和地理分布,而且取决于云量季节变化和地理分布.(2)就年平均而言,由于硫酸盐辐射强迫的影响,模拟区域内大部分地区普遍降温.降温比较明显的区域位于110°E以东、40°N以南的中国大陆地区,超过-0.1℃.其中华北平原和长江中游的湖南、湖北形成两个降温大值中心,幅度超过-0.2℃.(3)地面温度响应呈现出明显的区域季节变化特征.冬春季节,温度响应与辐射强迫之间满足较好的对应关系;夏秋季节,二者呈现出复杂的非线性关系.     

关于沙文諾夫-昂斯川姆經驗公式中系数k值对我国情况的修改

近年来,在苏联热量平衡的研究中,曾利用沙文诺夫-昂斯川姆经验公式计算地表面的总辐射:Q=90[1-(1-k)n].(1)式中Q和Q_0分别为实际情况下和晴空情况下的总辐射;k为全天有云时Q与Q_0的比值,这里只考虑了年平均k值随緯度的变化;n为以分数表示的平均总云量,通常利用该公式确定总辐射。月平均值时,误差为10％;年平均误差小于5％。     

干旱气候条件下多种潜在蒸发量估算方法对比研究

潜在蒸发量表征局地大气蒸发能力,是研究陆面过程和水文循环的关键参量。基于中国科学院临泽内陆河流域研究站2015 2016年实测气象数据,对比分析了综合法、辐射法和温度法共10种潜在蒸发量计算公式在河西走廊中段干旱气候条件下的差异,并将计算结果与台站内E601型和Φ20型蒸发皿记录的蒸发量数据进行了统计分析。结果表明:(1)影响E601型和Φ20型蒸发量的气象因素主要为饱和水气压差、净辐射和温度;(2)两种蒸发皿折算系数(ETp-E601/ETp-Φ20)的算术平均法和一元线性回归法计算值分别为0.65和0.62;(3)总体上综合法最适用,其次是辐射法,基于温度的各方法适用性最差;(4)综合法中FAO-56法最优,与E601型蒸发皿值拟合值为1.02(R2=0.70);其次是基于辐射的Doorenbos-Pruitt法,与Φ20型蒸发皿值拟合值为0.78(R2=0.85)。以上研究结果为估算我国西北干旱区及类似环境下潜在蒸发量提供了方法上的借鉴。     

正压大气中地转偏差引起的非线性Rossby波

正压大气中的非线性波动的研究业已在60年代开始,70年代到80年代取得了丰硕的成果。在我国巢纪平等(1980)首先讨论了旋转大气中的正压Rossby椭圆余弦波。之后刘式适、黄思训等也做了大量的工作。特别是刘式适等,鉴于以前的工作多采用多尺度方法,比如约化摄动法,而这种方法中的G-M变换本身就意味着将要导出的结果。考虑到长波的弱非线性近似,将非线性项在平衡点附近展开为Taylor级数,求得了方程的非线性近似解。黄思训等认为应用展开法只能求得原方程的近似解,问题的解析解尚未找到。于是利用类似的模式导出了方程的解析解,且给出了存在非线性     

最优测站距离、最优垂直分层和最优观测时间间隔的决定

考虑观测误差、截断误差和数值天气预报的需要,本文给出了决定最优相邻测站之间距离d、最优垂直网格距Δp和最优观测时间间隔Δt的公式。这些公式和预报所考虑的最短波长,以及最大观测误差和波幅的比有关,对于不同尺度的天气系统,结果很不一样。 对于过滤大气模式,d,Δp,Δt的值和世界气象组织对全球观测系统所要求的相近;但对于原始方程大气模式,Δt的值则远比过滤大气模式的为小。因而,用现有常规观测系统研究大气运动的快过程并不适宜,只能借助于以地面为基础的和以空间为基础的最优的混合观测系统才有可能。     

长波的垂直結构和它的移动与发展的关系

本文利用线性两层模式討論了对流层上部和下部扰动的发展和移动,以及它們之間相互关系。有以下主要結果: 1.一般常用的“溫度波落后于气压波,扰动发展”这一規則,对于超长波(波长大于10000公里)只适用于对流层上部,对于波长为7000公里左右的长波自对流层中部以上皆可应用,对于較短的长波整个对流层皆可应用。 2。当槽线或脊线随高度向西傾斜时,扰动的上层发展,下层阻尼;向东傾斜时,上层阻尼,下层发展;当时,上下层同时发展. 3.溫度波和高度波的移速可以不同,甚至方向可以相反;无論在上层或下层,当脊移进輻散区或槽移进輻合区时,扰动发展;当脊移进輻合区或槽移进輻散区时,扰动阻尼. 4.扰动的振幅和移速随时間而变,它不仅决定于基本流場的参数和扰动的波长,同时决定于扰动本身的上下結构. 5.周期性变化的稳定波在发展时期,其振幅的发展一天可达两倍半以上.因此日常所观測到的环流的巨大变化是否都属于一般所謂的西风带不稳定的現象值得深入研究.     

关于处理初始资料和取某些参数的问题

针对目前处理初始资料中存在的问题,提出了一个满足能量守恒和整层无辐散等约束条件的变分方案,并就风的调整进行了试验。结果表明,在严格满足约束条件的情况下,调整后的风及其分布比调整前改变并不大。调整值可以作为预报方程的初值。 文中还针对某些参数因人、因地而取值不同的问题,提出了一个可以随流场、温度场调整的方案。     

行星反照率的取值和假设的讨论

首先分析了Wang的有关行星反照率假设的错误之处,而后分别对Budyko、North的行星反照率假设提出修改方案,最后提出了有关行星反照率的非线性分段、反馈假设:     

An empirical relationship between temperature,vapour pressure deficit and wind speed and evaporation during a winter chinook

Summary Evaporation rates determined by energy balance and bulk transfer equations and confirmed with soil moisture sampling was regressed against average daytime temperature, vapour pressure deficit and wind speed over several chinook events between 1986 and 1988. The equationE = 0.45 exp (0.35 + 0.025 — 0.133 [e ^* —e]) yielded reasonable estimates of evaporation with surface soil moisture between saturation and near wilting point.E is evaporation in mmd ^–1,T, u ande ^* ande are temperature (°C), wind speed (ms^–1), saturation vapour pressure and vapour pressure (mb) respectively. The overbar denotes daytime average.With 8 Figures     

近40年京津冀蒸发皿蒸发量变化特征及影响因子

为了研究京津冀地区蒸发皿蒸发量的变化特征及成因,在京津冀地区200多个气象站中选择资料序列完整且具有较长时间序列、测站环境评分都在70分以上(按照中国气象局对测站探测环境评分标准评分)、均匀分布的87个气象站,利用1970—2013年京津冀地区87个气象站蒸发皿蒸发量以及其他气象要素的观测资料,采用线性倾向估计法和完全相关系数法,分析近44年来京津冀蒸发量变化特征及影响因子。结果表明,近44年来,京津冀地区年、季蒸发量呈明显下降趋势。全年蒸发量减少速率由大到小分别为:山前平原区太行山区冀东平原区燕山丘陵区冀北高原区(蒸发速率由北向南逐渐增大);四季中下降速率为:春季秋季冬季夏季。分析蒸发量与影响因子的完全相关系数发现,气温日较差、日照时数和平均风速是影响京津冀地区蒸发皿蒸发量变化的主要因子,在平原地区,平均风速是主导因子;在山区和高原地区,日照时数是主导因子。     

An annual cycle of vegetation in a GCM. Part I: implementation and impact on evaporation

The sensitivity of evaporation to a prescribed vegetation annual cycle is examined globally in the Met Office Hadley Centre Unified Model (HadAM3) which incorporates the Met Office Surface Exchange Scheme (MOSES2) as the land surface scheme. A vegetation annual cycle for each plant functional type in each grid box is derived based on satellite estimates of Leaf Area Index (LAI) obtained from the nine-year International Satellite Land Surface Climatology Project II dataset. The prescribed model vegetation seasonality consists of annual cycles of a number of structural vegetation characteristics including LAI as well as canopy height, surface roughness, canopy water capacity, and canopy heat capacity, which themselves are based on empirical relationships with LAI. An annual cycle of surface albedo, which in the model is a function of soil albedo, surface soil moisture, and LAI, is also modelled and agrees reasonably with observed estimates of the surface albedo annual cycle. Two 25-year numerical experiments are completed and compared: the first with vegetation characteristics held at annual mean values, the second with prescribed realistic seasonally varying vegetation. Initial analysis uncovered an unrealistically weak relationship between evaporation and vegetation state that is primarily due to the insensitivity of evapotranspiration to LAI. This weak relationship is strengthened by the adjustment of two MOSES2 parameters that together improve the models LAI-surface conductance relationship by comparison with observed and theoretical estimates. The extinction coefficient for photosynthetically active radiation, k _par , is adjusted downwards from 0.5 to 0.3, thereby enhancing the LAI-canopy conductance relationship. A canopy shading extinction coefficient, k _sh , that controls what fraction of the soil surface beneath a canopy is directly exposed to the overlying atmosphere is increased from 0.5 to 1.0, which effectively reduces soil evaporation under a dense canopy. When the experiments are repeated with the adjusted parameters, the relationship between evaporation and vegetation state is strengthened and is more spatially consistent. At nearly all locations, the annual cycle of evaporation is enhanced in the seasonally varying vegetation experiment. Evaporation is stronger during the peak of the growing season and, in the tropics, reduced transpiration during the dry season when LAI is small leads to significantly lower total evaporation.     

Effects of salinity upon evaporation from pans and shallow lakes near the Dead Sea

Summary Evaporation was evaluated for three shallow lakes near the Dead Sea with specific gravities (s.g.) of 1.26, 1.31 and 1.34, and for a hypothetical fresh lake of similar depth. The annual march of lake temperature was adequately predicted with an equilibrium temperature model. Predicted temperatures were only slightly affected by neglecting heat exchange between the lake and the underlying sediments. Modeled lake temperatures were then used in a modified Penman-type model and an alpha ratio model to generate evaporation estimates. The evaporation models were verified by comparison against 1950'ies water balance estimates of evaporation from the Dead Sea (s.g. about 1.18). Annual totals of evaporation predicted by the models for the shallow lakes declined from 2125 mm for fresh water (s.g. = 1.0) down to 588 mm for the most saline conditions (s.g. = 1.34). Evaporation was also measured from sunken pans in which s.g. was maintained at 1.0, 1.26, 1.31 and 1.34. Mean monthly pan coefficients (from lake/pan evaporation for equal s.g. values) ranged from 0.63 up to 1.03 as s.g. increased from 1.00 up to 1.34. The variations in coefficients are attributed to effects of salinity on the mechanisms that control the gain and loss of heat to the ponds and evaporation pans. The temperatures of the saline lakes were always somewhat warmer than the temperatures measured in the sunken pans, ranging from + 0.7 °C for s.g. of 1.26 up to + 1.3 °C for s.g. of 1.34; the corresponding value for the fresh condition was — 0.4 °C. The pan coefficients defined here for saline conditions will be useful for estimating actual water loss from brine-filled ponds used in commercial extraction of potash and other chemicals.With 2 Figures     

Effects of crop residue on soil and plant water evaporation in a dryland cotton system

Summary Dryland agricultural cropping systems emphasize sustaining crop yields with limited use of fertilizer while conserving both rain water and the soil. Conservation of these resources may be achieved with management systems that retain residues at the soil surface simultaneously modifying both its energy and water balance. A conservation practice used with cotton grown on erodible soils of the Texas High Plains is to plant cotton into chemically terminated wheat residues. In this study, the partitioning of daily and seasonal evapotranspiration (E _t) into soil and plant water evaporation was compared for a conventional and a terminated-wheat cotton crop using the numerical model ENWATBAL. The model was configured to account for the effects of residue on the radiative fluxes and by introducing an additional resistance to latent and sensible heat fluxes derived from measurements of wind speed and vapor conductance from a soil covered with wheat-stubble. Our results showed that seasonalE _t was similar in both systems and that cumulative soil water evaporation was 50% ofE _t in conventional cotton and 31% ofE _t in the wheat-stubble cotton. Calculated values ofE _t were in agreement with measured values. The main benefit of the wheat residues was to suppress soil water evaporation by intercepting irradiance early in the growing season when the crop leaf area index (LAI) was low. In semiarid regions LAI of dryland cotton seldom exceeds 2 and residues can improve water conservation. Measured soil temperatures showed that early in the season residues reduced temperature at 0.1 m depth by as much as 5°C and that differences between systems diminished with depth and over time. Residues increased lint yield per unit ofE _t while not modifying seasonalE _t and reducing cumulative soil water evaporation.With 8 Figures