Application of the Priestley-Taylor evaporation model to assess the influence of soil moisture on the evaporation from a large weighing lysimeter and class a pan

The influence of soil moisture on evaporation from a 6-m grass-covered lysimeter and from Class A pans was assessed for one summer using the -parameter of the Priestley-Taylor evaporation model appropriate for the individual surfaces computed on a daily basis. Net radiation over the pan was estimated from above-grass measurements using a correlation established between the two, using measurements made in the previous two summers. Changes in heat storage of the water were considered in the derivation of for the pan. A unique relationship for the particular conditions of the site was determined between the for the lysimeter and soil moisture, approaching 1.29 at soil moisture near field capacity, but decreasing to as low as 0.5 for dry soil. The corresponding relationship for the pan showed more scatter, but this was improved by using 5-day running means of evaporation and stratifying the data in terms of wind speed to yield a family of curves. Values for at wet soil conditions varied from 1.07 for 100 km day^–1 wind run to 1.17 for 250 km day^–1 wind run. For each curve, values of increased by about 20%; as the soil dried. The relationships may be used to reduce observed Class A pan evaporation to equivalent values for wet-soil conditions and to estimate near-surface soil moisture and actual evapotranspiration for this particular site. Extension of the technique to other areas requires derivation of similar relationships appropriate for those other locations     

降水时间随机性对月总降水量的影响

降水量在时间分布上呈现较大的随机性,极端降水事件尤为如此。受此影响,月初(月末) 1～5 d之内的累积降水量很可能会超过当月总降水量的50%乃至更多。对1961—2017年中国2 400多站点资料统计分析结果发现,月初(月末) 1～5 d累积降水量对当月总降水量显著影响事件的出现频次,在季节和空间分布上都有鲜明特征。主要包括:1)月初累积降水量对秋冬季中各月的总降水量影响更大,月末累积降水量对1—4月的月总降水量影响较大。2)受月初累积降水量的影响,显著站点数在某些年份的某些月份出现极大值;受单次事件显著影响的站点数占全国总站点数的30%～50%,此即对应着一次全国大范围的极端降水事件。3)受月初(月末)累积降水量显著影响的站点空间分布随季节变化呈现出明显空间集聚特征。     

A note on estimating the effect of a limited fetch on micrometeorological evaporation measurements

A formula for the effective fetch of micrometeorological evaporation measurements is derived by application of diffusion theory, using Calder's approximation of a uniform wind field and neutral atmospheric stability. This simplification allows estimation of the likely sampling error, which would result from an upwind step-change in evaporation rate, without change in roughness.     

Statistical downscaling of daily mean temperature, pan evaporation and precipitation for climate change scenarios in Haihe River, China

A statistical downscaling method (SDSM) was evaluated by simultaneously downscaling air temperature, evaporation, and precipitation in Haihe River basin, China. The data used for evaluation were large-scale atmospheric data encompassing daily NCEP/NCAR reanalysis data and the daily mean climate model results for scenarios A2 and B2 of the HadCM3 model. Selected as climate variables for downscaling were measured daily mean air temperature, pan evaporation, and precipitation data (1961–2000) from 11 weather stations in the Haihe River basin. The results obtained from SDSM showed that: (1) the pattern of change in and numerical values of the climate variables can be reasonably simulated, with the coefficients of determination between observed and downscaled mean temperature, pan evaporation, and precipitation being 99%, 93%, and 73%, respectively; (2) systematic errors existed in simulating extreme events, but the results were acceptable for practical applications; and (3) the mean air temperature would increase by about 0.7°C during 2011~2040; the total annual precipitation would decrease by about 7% in A2 scenario but increase by about 4% in B2 scenario; and there were no apparent changes in pan evaporation. It was concluded that in the next 30 years, climate would be warmer and drier, extreme events could be more intense, and autumn might be the most distinct season among all the changes.     

1960—2009年北京地区城市化背景下蒸发皿蒸发量的时空变化

利用1960—2009年北京地区20个气象台站的观测资料,分析了北京城区和郊区蒸发皿蒸发量的季节和年际变化趋势和特点,并探讨了城市化对北京地区局地气候的影响。结果表明:近50 a北京地区蒸发量有明显减小趋势,城区和郊区变化趋势分别为-88.1 mm/10a和-76.0 mm/10a。受城市化影响,北京城区蒸发量的变化主要与降水、日照时数、最低气温、气温日较差和平均风速的变化有关;郊区蒸发量的变化主要受相对湿度、日照时数、平均风速和空气饱和差的变化影响。总体而言,相对湿度、日照时数、最低气温、气温日较差和平均风速的变化对北京地区蒸发量的变化有显著影响。     

Changes of pan evaporation and reference evapotranspiration in the Yangtze River basin

Summary For the upper and mid-lower Yangtze River basin trends of pan evaporation and reference evapotranspiration are analysed from 1961 to 2000 using daily data of 115 stations. Both pan evaporation and reference evapotranspiration decreased during the summer months contributing most to the total annual reduction. This trend is more significant in the mid-lower than in the upper Yangtze reaches. The decreasing trends can be associated with trends in net radiation and wind speed. Results are compared with the 20th century evaporation simulated by the general circulation model (GCM, ECHAM5/MPI-OM). Also the GCM’s actual evaporation decreases contrasting an overall increase in air temperature.     

Tilt errors and precipitation effects in trivane measurements of turbulent fluxes over open water

For 390 ten-minute samples of turbulent flux, made with a trivane above a lake, the vertical alignment is determined within 0.1 ° through azimuth-dependent averaging. One degree of instrumental misalignment is found to produce an average tilt error of 9 ± 4% for momentum flux, and 4 ± 2% for heat flux. The tilt error in the vertical momentum flux depends mainly ons _u/u_*, and cannot be much diminished with impunity by high-pass pre-filtering of the turbulence signals. The effects of rain on trivane measurements of vertical velocity are shown to be negligible at high wind speeds, and adaptable to correction in any case.The normalized vertical velocity variance,s _w/u_*, appears to be proportional to the square root ofz/L for unstable stratification. For a wind speed range of 2 to 15 m s^–1, the eddy correlation stresses measured at 4- and 8-m heights can be reasonably well estimated by using a constant drag coefficientC _d=1.3 X 10^-3, while cup anemometer profile measurements give an overestimate of eddy stress at high wind speeds. A good stress estimate is also obtained from the elevation variance; it is suggested that trivane measurement of this variance might be made from a mobile platform, e.g., a moderately stabilized spar buoy.     

Important factors governing the incompatible trends of annual pan evaporation: evidence from a small scale region

Many studies reported the coexisting trends of decreasing and increasing pan evaporation in some large scale regions. This study proved that the coexisting trends also occurred in small scale region as well as in large scale region. To discover the important factors governing the incompatible trends of annual pan evaporation, annual climatic data of ten meteorological stations at the Liaohe Delta over recent 45 years were analyzed by the partial correlation analysis, and the results showed the strongest statistically correlation between annual relative humidity and annual pan evaporation. Researches on two extreme cases suggested there was obvious contrary trend between annual relative humidity and annual pan evaporation for one case, in despite of slight contrary trend for another case. Generally, annual relative humidity most likely was an important factor relating to the trend of annual pan evaporation. At the same time, an expanded urbanization and irrigation were seen around these meteorological stations. Urbanization and irrigation exerted opposite effects on pan evaporation, they therefore were speculated to be the ultimately inducements causing unbalanced relative humidity, and led to incompatible pan evaporation.     

Comparison of methods used in the measurement of precipitation and evaporation

Summary The measurement of evaporation and precipitation continues to be most problematic, particularly in terms of the accuracy of the instruments used and their standardization world-wide. This paper analyzes daily data from three rain gauges and two evaporimeters over a five-year period and correlates observed differences with the prevailing meteorological conditions. It was determined that ground-level gauges and large evaporation tanks provide the most acceptable and representative measurements from instruments currently in use. However, new developments are necessary for improved accuracy and world-wide adoption.With 2 Figures     

The influence of systematic errors on the asian summer monsoon circulation

1. IntroductionThe Asian summer monsoon circulation is a thermally driven circulation, which arisesprimarily from the temperature differences between the warmer continental areas of theNorthern Hemisphere and the oceans of the Southern Hemisphere. The complex feedback between the flow field and the heating, especially through the interaction between thelarge--scale flow and moist convection, is yet to be well understood. Nevertheless, this facetensures the prominence of the summer monsoon ci…     

The influence of surface cover and climate on energy partitioning and evaporation in a subarctic wetland

Energy partitioning and evaporation were measured over three wetland surfaces in a subarctic coastal marsh during pre-growing and growing periods. These surfaces included an alder/willow woodland, a sedge marsh and a raised backshore sedge meadow. A combination model analysis was used to assess the relative importance of surface resistance and meteorological conditions on the magnitude of the Bowen ratio, , during the growing period.Overall, the three surfaces experienced important site-to-site and seasonal differences in and evaporation, Q _E. During the non-foliated period, Q _E was largest and was smallest for the open water marsh, while the dry backshore site experienced the smallest Q _E and largest . The non-foliated woodland assumed intermediate values of and Q _E. After the vegetation covers were established, the woodland assumed the smallest and largest Q _E flux. It was also found that at the marsh site increased with the presence of a vegetation cover.Wind direction was always an important factor in determining Q _E and at all sites. was substantially larger and Q _E was smaller for onshore winds (i.e., originating from James Bay) than for offshore winds. The combination model analysis showed that canopy resistance at all sites was largest during warm offshore winds, which were associated with large saturation deficits. However, the effect of increased canopy resistance on during offshore winds was offset by a large climatological resistance, resulting in small values and large Q _E. When winds originated from James Bay, canopy resistance was smaller than for offshore winds, but the climatological resistance also was much smaller, resulting in larger and small Q _E. The results have important implications for changes in land cover and climate on the regional water balance.     

The influence of the ocean on the chemistry of precipitation in Nova Scotia*

Abstract

Between the fall of 1977 and December 1980, over 800 samples of precipitation were collected at 9 rural locations across Nova Scotia.

Average pH was 4.61, and an average conductivity of 25 μS cm^?1 confirmed the low ionic strength of rain and snow. Of all ions, chloride was the most abundant at 76 μeq L^?1 (2.7 mg L^?1). Oceanic origins were perceived as the source for chloride as well as for Na, Mg, 51 % of K, 21% of Ca, and 21% of SO₄, and the sea collectively accounted for 66% of all ions inNova Scotian precipitation. In contrast, the dominating ions in New York, New Hampshire, Ontario and Norway were H⁺ and SO₄.

In Nova Scotia, chloride concentrations in rain (mg L^?1) are a function of distance D (km) from the coast and may be described by the equation Cl [mg L^?1] = 4.5D^?0.42. It indicates that Cl concentrations are reduced by about 50% within 0.5 km of the coast, and 80% within 5 km. The continental North American chloride data examined are also consistent with the relationship.

The shape of the chloride curve is similar to curves others have developed from rain and lake water chemistry observations in Holland and the United Kingdom, although those, and other European data, indicate that the marine influence is less pronounced in northeastern North America.

The marine influence of precipitation chemistry on Nova Scotia has a maximum seasonal amplitude during the winter.     

The influence of systematic errors in the Southeast Pacific on ENSO variability and prediction in a coupled GCM

The impact of the warm SST bias in the Southeast Pacific (SEP) on the quality of seasonal and interannual variability and ENSO prediction in a coupled GCM is investigated. The reduction of this bias is achieved by means of empirical heat flux correction that is constant in time. It leads to a wide range of changes in the tropical Pacific climate including enhanced southeast trades, well-defined dry zone in the SEP, better simulation of the South Pacific Convergence Zone and stronger cross-equatorial asymmetry of the mean state in the eastern Pacific. As a result of the mean climate correction, significant improvements in the simulation of the seasonal cycle of the oceanic and atmospheric states are also observed both at the equator and basin-wide. Due to more realistic simulation of the seasonal evolution of the cold tongue, tropical convection and surface winds in the corrected version of the model, phase-lock of ENSO to the annual cycle looses its strong semi-annual component and becomes quite similar to the observed, although the amplitude of ENSO is reduced. Zonal wind stress response to the SST anomalies in the central-eastern Pacific also becomes more realistic. ENSO retrospective forecast experiments conducted with the directly coupled and the flux-corrected versions of the model demonstrate that deficiencies in the seasonal evolution of the cold tongue/Inter-Tropical Convergence Zone complex (that were largely due to the SEP bias in this model) and the related errors in the ENSO phase-lock to the annual cycle can seriously degrade ENSO prediction. By reducing these errors, ENSO predictive skill in the coupled model was substantially enhanced.     

1961-2010年青海高原蒸发皿蒸发量变化及其对水资源的影响

利用1961-2010年青海省气象观测资料,分析了青海高原近50年蒸发皿蒸发量的时空分布特征和变化趋势,并采用偏相关及主成分分析法,探讨了青海高原蒸发皿蒸发量变化的气候成因及其对水资源的影响。结果表明：近50 a来青海高原蒸发皿蒸发量呈显著下降趋势,它是热力、水分、动力因子综合作用的结果,在三类因子中,动力及水分因子对蒸发皿蒸发量的影响较大,而热力因子相对较小;区域分析表明,影响东部农业区和柴达木盆地蒸发量的主导因子是平均风速和相对湿度,三江源区为相对湿度,而唐古拉山区为气温日较差。通过分析黄河上游可能蒸散量与地表水资源的关系发现,蒸散量对地表水资源的负效应十分显著,其中夏季蒸散量对于平均流量的影响最为显著,而秋季平均流量对蒸散量的响应最为敏感。     

江西及其临近区域同化系统中不同季节背景误差协方差特征及其对降水预报影响

在不同季节背景下,对比分析多元变量相关的背景误差协方差特征,了解其在天气过程中的作用,可以改进同化系统性能,提高降水数值预报水平。对比分析汛期和非汛期江西及其临近区域多元变量相关的背景误差协方差特征,分别选取2019年汛期和非汛期的2次降水过程,设计2组循环同化试验,探讨多元变量相关的背景误差协方差对江西降水预报效果的影响。结果表明,相较于非汛期,汛期分析变量对风场、温度场和水汽场的贡献值整体上要更大,且汛期各个控制变量的背景场误差更为显著。多元变量试验的降水预报评估效果整体上更好,其汛期预报效果改善更显著。汛期与非汛期的多元变量试验降水预报结果更接近实况,且相对非汛期降水而言,汛期多元变量试验模拟效果更好,模拟的降水分布及强度与实况更为接近。     

降水对气溶胶粒子清除的参数化

本文主要讨论了碰并系数、雨滴谱和气溶胶谱对湿清除率的影响.在0.1μm相似文献   

The influence of precipitation intensity growth on the urban drainage systems designing

For 50 years of long observation period (1960–2009), on a high level of statistical significance (95 %), a decreasing trend of annual precipitation amounts and an increasing trend of the number of rainy days during the year (64 %) were found. For the seasonal changes (V–X), similarly, there was found a statistically significant (94 %) decreasing precipitation amount trend and an increasing trend of the number of rainy days (50 %). As far as the intensity of maximum precipitation is concerned, a very statistically significant increasing trend (95 %) was found. Taking as the basis, the model for a trend, defined for the period of 1960–2009, the increase of weighted average interval values of maximum precipitation amounts (h?≥?0.75?t ^0.5) in the year 2059 was estimated to be about 26 %, in comparison with the starting year 1960. An increasing trend of maximum precipitation frequency in Wroc?aw was also proved. To a safe sewerage systems designing in Wroc?aw according to current standards (EN 752 2008; DWA-A118 2006), the precipitation frequency to the simulations of excessive accumulation occurrences to the land level should be changed.     

地面微波辐射计与测定区域性降水的初步试验

一、前言 被动式大气微波遥感探测是近十年来发展起来的一门崭新的遥感技术。自1968年以来,卫星运载的微波辐射计在遥感大气温度、云中含水量、降水强度及水汽密度等方面都取得了显著的成绩。与此同时,地面微波遥感探测也获得相应的发展,不仅类似空间遥感可以实现温度、水汽的反演,而且还将大大发挥微波探测雨云的特长,能有效地测得云中含水量、云中温度、以及降水强度等参数,这对云雾物理、人工影响天气的发展必将起到积极的作用。