蒸发势的一种计算方法

讨论蒸发势的一种经验计算方法, 考虑了平均气温、相对湿度、风速3种要素.其数值与彭曼蒸发势值, 与用E601蒸发器、小型蒸发器观测的蒸发量 (以下分别简称E601蒸发量, 小型蒸发量) 作相关分析, 相关系数都在极显著水平以上, 而且很稳定.因此, 初步认为这种计算法适合于本地.本计算方法通俗易懂, 便于掌握和使用, 与有关指标 (例如干热风指标) 可以较好地衔接.利用本计算方法所得结果在评估水分盈亏时取得了明显的成效, 在干旱和干热风分析中有重要的实际意义.     

气温变化对黄河流域蒸发能力的影响

气温是影响流域蒸发的一个重要因素,根据黄河流域蒸发能力与气温的关系,建立了简洁且实用的指数型蒸发能力估算公式,分析了气温变化对流域蒸发能力的影响。结果表明:黄河流域简洁指数型公式具有与高桥浩一郎公式同样好的蒸发能力估算效果,在气温升高1℃的情况下,流域蒸发能力约增加5.0%~7.0%;干燥系数约为3时,蒸发能力随气温的变率最大。     

The Effect of Orography on Evaporation

The effect of orography on the spatial variability of surface evaporation is studied numerically for two hill heights and two prescribed forms of surface resistance. A numerical model of the planetary boundary layer carrying scalars of temperature and specific humidity, and with a surface energy balance scheme, is employed. It is found that the difference in mean evaporation between model runs with hills and analogous runs for flat terrain may be explained primarily by an increase in surface area and adiabatic cooling at the hill surface.     

Evaporation over a Heterogeneous Land Surface: EVA_GRIPS and the LITFASS-2003 Experiment—An Overview

The Evaporation at Grid/Pixel Scale (EVA_GRIPS) project was realised in order to determine the area-averaged evaporation over a heterogeneous land surface at the scale of a grid box of a regional numerical weather prediction or climate model, and at the scale of a pixel of a satellite image. EVA_GRIPS combined surface-based and airborne measurements, satellite data analysis, and numerical modelling activities. A mesoscale field experiment, LITFASS-2003, was carried out in the heterogeneous landscape around the Meteorological Observatory Lindenberg (MOL) of the German Meteorological Service in May and June, 2003. The experiment was embedded in the comprehensive, operational measurement program of the MOL. Experimental determination of surface fluxes on a variety of spatial scales was achieved by employing micrometeorological flux stations, scintillometers, a combination of ground-based remote sensing instruments, and the Helipod, a turbulence probe carried by a helicopter. Surface energy fluxes were also derived from satellite data. Modelling work included the use of different Soil–Vegetation–Atmosphere Transfer schemes, a large-eddy simulation model and three mesoscale atmospheric models. The paper gives an overview on the background of EVA_GRIPS, and on the measurements and meteorological conditions during LITFASS-2003. A few general results are discussed.     

2012年太湖蒸发量变化特征及蒸发模型评估研究

湖泊蒸发是全球能量分布,水文循环的重要组成部分,同时是气候及生态系统环境变化的指示因子。运用太湖湖上观测平台大浦口站2012年涡度相关数据分析了太湖蒸发量的月变化及日变化特征,并评估了11种蒸发模型。结果表明：太湖2012年总蒸发量为1066.2 mm。潜热通量是太湖净辐射能量分配中的主导项, 2012年太湖地区潜热通量占净辐射通量的91.9%。2～7月为太湖水体储热阶段,当净辐射在7月达到最大值时,蒸发值也达到最大值;净辐射8月开始减少,至12月达到最小值,期间湖体储热释放,使得蒸发量在2月才达到最小值。采用涡度相关系统观测太湖蒸发量的数据评估了11种蒸发模型,分别从年蒸发总量和蒸发量月变化特征来探讨模型对于太湖蒸发量计算的适用性,其中以波文比能量平衡模型表现最好,与涡度相关观测值的相关系数为0.99,中心化均方根误差为4.50 mm month^-1。     

A Study on Frontal Motion over Orography

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蜜蜂舐水对蒸发量的影响及对策

蜜蜂采舐蒸发水量,一直不被人们注意,但通过对养蜂人走访调查,并与历年同期蒸发记录对比分析,排除大风等天气现象对蒸发量的影响后,发现蜜蜂舐水干扰后的蒸发结果异常,及时采取措施合理阻断蜜蜂舐水,尽量减少对蒸发的影响。     

分层气流条件下地形降水的二维理想数值试验

利用WRF v3.5中尺度数值模式,在条件不稳定层结下,针对分层气流(基本气流风速和大气湿浮力频率呈二层均匀分布)过山时,地形对降水的影响进行了多组二维理想数值试验,以研究不同高度、尺度山脉和不同方向基本气流对降水形态和分布的影响。模拟结果表明,地形重力波触发对流是地形降水的主要机制之一,地形波的特征(波长、振幅)和传播均受到地形和基本气流的影响,其中,强基本气流流经高而陡峭的山脉时,更容易在其背风坡捕捉到重力波,地形降水呈现多种模态,反之亦然;当改变基本气流与山脉交角时,主要通过影响地形强迫抬升速度、基流对波动稳定性发展来进一步影响地形降水的强度和分布。     

黔东南气温变化对蒸发皿蒸发量的影响分析

利用1980-2010年黔东南地区16个地面气象站逐月实测资料,采用灰色关联度方法分析了蒸发皿蒸发量对各气象要素的影响程度,通过经验正交函数分解方法(EOF)提取了第一特征向量场的时间系数并进行了Mann-Kendall突变检验和线性倾向估计分析,以及利用非线性回归方法建立数理模型确定气温变化对蒸发皿蒸发量的影响等。结果表明,黔东南地区的蒸发皿蒸发量与气温、湿度、降水量等因子有关系,并与气温的关系最为密切;同时,该地区气温出现了明显的升温趋势,即20世纪90年代中期是该地区年气温突变的关键时期,其气温倾向率为0.25℃.(10a)-1,通过了α=0.05显著性水平检验;在气温升高1℃的情况下,蒸发皿蒸发量增加了5.93%～8.04%,并自东向西逐渐递减,与海拔呈反相关关系。     

Evaluating a Model of Evaporation and Transpiration with Observations in a Partially Wet Douglas-Fir Forest

The Penman–Monteith equation is extended to describe evaporation of intercepted rain, transpiration and the interaction between these processes in a single explicit function. This single-layer model simulates the effects of heat exchange, stomatal blocking and changed humidity deficit close to the canopy as a function of canopywater storage. Evaporation depends on the distribution of water over the canopy and the energy exchange between wet and dry parts. Transpiration depends on the dry canopy surface resistance that is described with a Jarvis-type response. The explicit functions obtained for water vapour fluxes facilitate a straightforward identificationof the various processes. Canopy water storage amounts and xylem sapflow were measured simultaneously during drying episodes after rainfall in a dense, partially wet, Douglas-fir forest. Estimates of evaporation and transpiration rates are derived from these observations. The analysis shows that evaporation induced transpirationreduction is mainly caused by energy consumption. Changes in water vapour deficit have a minor effect due to a compensating stomatal reaction. The remaining difference between observed and modelled transpiration reduction can be attributed to partial blocking of stomata by the water layer.     

条件不稳定湿大气中三维理想地形上空对流的动力学特征

条件不稳定湿大气情况下,气流经过三维地形可以形成不同性质的对流系统以及不同特征的地形流结构,其对流系统、地形流的性质主要取决于地形上空的对流触发、对流-地形流-重力波三者之间的相互作用,同样这些过程对于地形降水的性质、分布起重要的作用.根据不同湿Fr数(Froude number),湿条件不稳定大气经过三维小尺度山地上空时其对流和地形流动存在4种不同的流域(flow regirnes):(1)下游传播对流模态;(2)上游传播和下游传播共存对流模态;(3)山峰附近准静止和下游传播共存对流模态;(4)下坡稳定和下游传播对流共存模态.地形上空对流系统主要可以通过两种不同机制形成:(1)地形直接的抬升或减速作用;(2)在地形流形成后,由于地形流本身特性(如上游分离、背风涡旋和下坡重力波破碎)触发.在较大的Fr数情况下,地形上空对流生成后反过来可以破坏上、下游的地形流结构,但对背风坡的重力波破碎影响较小.不同初始对流有效位能(CAPE)不仅可以影响对流系统的传播、发展,而且可以影响整体地形流性质.较低的初始CAPE有利于地形流的形成,此时对流对地形流结构特征的影响相对较小,其流场性质与低Fr数流域性质相似.     

小型蒸发器对E-601B蒸发器的折算系数

为了便于将过去40多年的小型蒸发器观测资料与E-601B蒸发器观测资料衔接使用，对全国618个基准和基本站直径20 cm小型蒸发器与E-601B蒸发器3年平行对比观测结果进行了统计，按省（市）给出了这两种仪器的月、年平均折算系数值及年折算系数的全国分布图，并给出了相应的标准差和相对标准差。     

Note on a Parametric Relation for Separating Flow over a Rough Hill

A parametrization method used to account for the effects of flow separation and wall roughness on the lower boundary condition for turbulent boundary layers is investigated against direct numerical simulation and laser Doppler anemometry data. The numerical simulation represents flow over a smooth, flat surface with a prescribed external adverse pressure gradient. The water-channel experiments cover flow over smooth and rough hills for two specified Reynolds numbers. Global optimization algorithms based on four different direct search methods are used to assess the parametrization function, C, in terms of local mean velocity profiles and the parametrization parameters u _* (friction velocity), ∂ _x p (local pressure gradient), z ₀ (effective roughness) and d (zero-plane displacement). The study investigates regions of attached and reversed flows, and forty-two velocity profiles are compared with the proposed expression for the function C, including two profiles that satisfy the solution of Stratford.     

1957-2009年南澳蒸发量变化特征及影响因子

利用1957-2009年南澳县小型蒸发皿蒸发量资料,分析了南澳蒸发量的气候变化趋势.结果表明:南澳10月蒸发量最大,2月蒸发量最少;秋季蒸发量最大,夏季次之,冬季最少.1957-2009年蒸发量呈明显下降趋势,20世纪60-90年代基本上是锐减,21世纪的第1个10 a反而上升,平均以7.2mm/a的趋势下降;11月减...     

Precipitation and evaporation budgets over the Baltic Proper: observations and modelling

Precipitation and evaporation budgets over the Baltic Sea were studied in a concerted project called PEP in BALTEX (Pilot study of Evaporation and Precipitation in the Baltic Sea), combining extensive field measurements and modelling efforts. Eddy-correlation-measurements of turbulent heat flux were made on a semi-continuous basis for a 12 month period at four well-exposed coastal sites in the Baltic Proper (the main basin of the Baltic Sea). Precipitation was measured at land-based sites with standard gauges and on four merchant ships travelling between Germany and Finland with the aid of specially designed ship rain gauges (SRGs). The evaporation and precipitation regime of the Baltic Sea was modelled for a 12 month period by applying a wide range of numerical models: the operational atmospheric High Resolution Limited Area Model (HIRLAM, Swedish and Finnish versions), the German atmospheric REgional-scale MOdel, REMO, the operational German Europe Model (only precipitation), the oceanographic model PROBE-Baltic, and two models that use interpolation of ground-based data, the Swedish MESAN model of SMHI and a German model of IFM-GEOMAR Kiel. Modelled precipitation was compared with SRG measurements on board the ships. A reasonable correlation was obtained, but the regional-scale models and MESAN gave some 20% higher precipitation over the sea than is measured. Bulk parameterisation schemes for evaporation were evaluated against measurements. A constant value of C_HN and C_EN with wind speed, underestimated large fluxes of both sensible and latent heat flux. The limited area models do not resolve the influence of the height of the marine boundary layer in coastal zones and the entrainment (on the surface fluxes), which may explain the observed low correlations between modelled and measured latent heat fluxes. Estimates of evaporation, E, and precipitation, P, for the entire Baltic Proper were made with several models for a 12 month period. While the annual variation was well represented by all predictions, there are still important differences in the annual means. Evaporation ranges from 509 to 625 mm year^-1 and precipitation between 624 and 805 mm year^-1 for this particular 12 month period. Taking the results of model verification from the present study into account, the best estimate of P-E is about 100 ± 50 mm for this particular 12 month period. But the annual mean of P-E varies considerably from year to year. This is reflected in simulations with the PROBE-Baltic model for an 18 year period, which gave 95 mm year^-1 for the 12 month period studied here and 32 mm year^-1 as an average for 18 years.     

1981—2010年西藏怒江流域潜在蒸发量的时空变化

利用1981—2010年怒江流域9个站月平均最高气温、最低气温、降水量、风速、相对湿度、日照时数等资料,应用Penman-Monteith模型,采用气候倾向率、R/S等方法分析了潜在蒸发量变化的趋势性和持续性,并探讨了影响潜在蒸发量的气象因子。结果表明：近30年怒江流域四季潜在蒸发量趋于减少,年潜在蒸发量以18.4 mm?(10a)-1的速率显著减少。夏、秋、冬季和年潜在蒸发量具有持续性,未来将持续减少,尤其是冬季。在年代际尺度上,四季潜在蒸发量1980年代为正距平,1990和2000年代均为负距平。风速减小是四季潜在蒸发量减少的主要因素,不过春季潜在蒸发量的减少与降水量的显著增加也有关,且夏季气温日较差的显著变小对潜在蒸发量减少的作用不可忽视。     

金塔绿洲土壤中蒸发/凝结过程的初步分析

利用2005年6月27日～7月4日金塔绿洲地表及0.40m土壤温度观测资料作为边界条件,结合一维土壤热传导方程计算了该时段0.05,0.10和0.20m深处的土壤温度。通过比较同时段观测值与计算值的观测,发现0.05m深处的土壤温度计算值与观测值的差异最大。结果表明,在方程中只需简单考虑浅层土壤蒸发/凝结过程,便可以使...     

长江流域潜在蒸发量和实际蒸发量的关系

针对“蒸发悖论”科学问题,从长江流域实际蒸发量变化的原因着手,探讨实际蒸发量与潜在蒸发量之间的关系。研究结果表明：一般情况下当干燥度指数R<0.8时,实际蒸发量与潜在蒸发量为明显的正相反关系,当0.81.0时,实际蒸发量与潜在蒸发量为明显的互补关系。     

Experimental calibration of a cost-effective X-band weather radar for climate ecological studies in southern Ecuador

In this paper setup, operational problems and a straightforward calibration approach for a cost-effective X-Band radar are presented. The LAWR (Local Area Weather Radar) system is based on conventional ship radar technology which is adapted to register rainfall within a range of about 60 km with a spatial resolution of 500 m per pixel. The instrument offers neither Doppler processing nor vertical scan capabilities but uses 20° wide (vertical) beam. The calibration suffers from an unfavorably distributed and very sparse rain gauge network, heavy clutter contamination of the signal and obstructions by surrounding terrain. A specific scaling approach is developed, that includes satellite data on cloud frequency and distribution, to overcome these limitations. Observed clutter is removed and missing values are replaced by bilinear interpolation of the undisturbed signals. A temporal and spatial bias of the radar signal is corrected using an omni-directional spatial distribution hypothesis. This is possible because of the location of the radar site in the transition zone between high rainfall on the eastern Andean slopes and low rainfall on the leeward side. A further limitation of the system is that the LAWR does not provide information on the measured reflectivity Z but dimensionless counts (8 bit resolution). Calibration is performed assuming a linear relation between radar output and rainfall as recommended by the systems manufacturer. The intercomparison of rain gauge and scatterometer data with calibrated radar rainfall reveals a good performance of the developed calibration approach.     

地形对门头沟一次大暴雨动力作用的数值研究

2002年6月24—25日,北京门头沟附近发生了一次大暴雨过程。为探讨地形在本次过程中的动力作用,采用美国俄克拉荷马大学风暴分析预测中心开发的ARPS模式,对大暴雨过程进行了数值试验。控制试验采用27、9 km双重单向嵌套网格,网格覆盖范围约为3000 km×3000 km、900 km×900 km。两层网格均采用全物理过程,使用的都是全球30″的地形资料。在控制试验的基础上,进行了3组敏感性试验:第1组试验采用干过程模拟,即不考虑凝结潜热的作用;第2组试验将地形整体向东/西平移1°;第3组试验是将门头沟西部的局地地形抠除一部分。试验结果表明,在不考虑凝结潜热作用时,东南风气流仍然可以爬升到2 km以上,超过了大气的抬升凝结高度,证实了地形的动力作用是本次大暴雨的触发机制;将地形向东/西平移1°后,由于大气的对流稳定度发生了改变,模拟的降水强度和落区也发生了变化,表明山坡和山顶的对流不稳定大气是导致本次大暴雨的必要条件;抠除局地地形后,模拟的降水量也发生了不同程度的改变,再次证明大暴雨是在多尺度地形以及一定的天气系统配置下产生的。