4种蒸发波导模型的对比与分析     

刘立行  李煜斌  高志球  毕雪岩  朱光明 《气象科学》2019,39(1):78-92

蒸发波导模型常用来计算海上蒸发波导高度。为了认识当前不同蒸发波导模型之间的差异和方法,本文选取了目前使用广泛的4种蒸发波导模型(即P-J模型、Babin模型、NPS模型和伪折射率模型)进行对比和分析。本文首先探讨了在理想情况下它们对气象要素的敏感性,随后并利用我国南海近海大气层观测试验数据对比了这4种模型的蒸发波导高度计算结果。分析表明:相对湿度、风速和气—海温差的变化对4种模型的计算都有着较大的影响,特别是在不稳定层结状况下,4种模型计算得到的蒸发波导高度都随着相对湿度的增大而降低、随着风速的增大而增高。Babin模型和NPS模型计算的波导高度较为一致,伪折射率模型与前两种模型的计算结果存在差异,而P-J模型与其他3种模型存在较明显的偏差。基于南海气象数据的计算结果表明,不同蒸发波导模型在该海域蒸发波导的模拟结果略有不同,但4种模型计算得到的波导高度日变化变化趋势较为一致,波导高度极低值常出现在早晨,而极高值常出现在傍晚。  相似文献   

昆明呈贡石灰岩上覆红黏土干缩裂隙的温度效应     

何岱洵 《地质与勘探》2023,59(5):1083-1092

温度是影响土体干缩开裂的重要外部环境因素之一。为研究温度对红黏土干缩裂隙的影响,以昆明呈贡石灰岩上覆红黏土为对象,经风干、碾碎和筛分后,选取2 mm以下的细颗粒,用正方形钢化玻璃容器制备9个厚度为10 mm的饱和泥浆样,分成3组,每组3个平行样,利用控温烘箱分别进行30℃、50℃和70℃的干燥试验,试验过程中定时称重试样和对土样表面进行拍照,然后用PCAS软件对照片进行图像处理。结果表明：红黏土的蒸发过程可分为3个阶段,干缩裂隙的形成和发展可分为5个阶段;温度升高,干燥完成时间减短,常速率阶段的蒸发速率和蒸发量增大,最终含水率降低;初始临界含水率随温度升高而增大;随着土体含水率持续减小,表面裂隙率先缓慢增加,然后快速增大,最后趋于稳定;温度升高,裂隙交点数、裂隙条数、裂隙总长度和土块数减少,裂隙平均长度、裂隙平均宽度、表面裂隙率、土块平均面积、土块最大面积、干缩厚度和干密度增大。温度显著影响红黏土的水分蒸发过程,干缩裂隙的形成和发展,以及表面裂隙结构和形态。  相似文献   

Evaluation of the Residual Mass Fractionation in High-Precision Cr Isotopic Analysis with TIMS     

Tetsuya Yokoyama  Yusuke Ohkuma  Keiji Nishikawa  Koki Sumiya  Ikshu Gautam 《Geostandards and Geoanalytical Research》2023,47(2):415-435

The Cr isotope ratios of terrestrial and extra-terrestrial materials are emerging as one of the most important tracers in geosciences. Previous studies on Cr isotopic measurements using TIMS have found that there is residual Cr isotopic fractionation between the mass-fractionation-corrected ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios, which may cause an offset of obtained ratios from the reference values. The residual fractionation was thought to be caused by the evaporation of Cr-oxide species during thermal ionisation, but the mechanism by which this residual fractionation could be reduced remained unclear. Here we revisit the issue of residual fractionation and propose that this problem can be alleviated by utilising W filaments instead of conventionally used Re filaments for Cr ionisation. Using W filaments, the formation of CrO⁺ was suppressed during heating as the filament temperature was ~ 100 °C lower than when Re filaments were used. In repeated measurement of a carbonaceous chondrite, the intermediate precisions of ⁵³Cr/⁵²Cr and ⁵⁴Cr/⁵²Cr ratios in the W filament runs were two to three times better than those of the Re filament runs. Therefore, the new finding of this study will be of key importance for future studies of Cr isotopes for terrestrial and extra-terrestrial materials.  相似文献   

Evaporation from seasonally frozen bare and vegetated ground at various groundwater table depths in the Ordos Basin,Northwest China     

Zaiyong Zhang  Wenke Wang  Chengcheng Gong  Zhoufeng Wang  Lei Duan  Tian‐chyi Jim Yeh  Peiyuan Yu 《水文研究》2019,33(9):1338-1348

In cold climates, the process of freezing–thawing significantly affects the ground surface heat balance and water balance. To better understand the mechanism of evaporation from seasonally frozen soils, we performed field experiments at different water table depths on vegetated and bare ground in a semiarid region in China. Soil moisture and temperature, air temperature, precipitation, and water table depths were measured over a 5‐month period (November 1, 2016, to March 14, 2017). The evaporation, which was calculated by a mass balance method, was high in the periods of thawing and low in the periods of freezing. Increased water table depth in the freezing period led to high soil moisture in the upper soil layer, whereas lower initial groundwater levels during freezing–thawing decreased the cumulative evaporation. The extent of evaporation from the bare ground was the same in summer as in winter. These results indicate that a noteworthy amount of evaporation from the bare ground is present during freezing–thawing. Finally, the roots of Salix psammophila could increase the soil temperature. This study presents an insight into the joint effects of soil moisture, temperature, ground vegetation, and water table depths on the evaporation from seasonally frozen soils. Furthermore, it also has important implications for water management in seasonally frozen areas.  相似文献   

A Raman investigation on the boron form occurring in salt lake brine during evaporation          下载免费PDF全文

彭姣玉  陈婧  王兴鹏  董亚萍  李武 《盐湖研究》2019,27(1)

Boron resources are abundant in Da Qaidam salt lake of Qaidamu Basin. It has been given great attention for the polyborate species present in brine. In this study, the Raman spectroscopy was applied to investigate the existing-form of boron in brine during evaporation. The prepared solutions of MgO·2B2O3-H2O, MgO·2B2O3-MgCl2 -H2O, and MgO·2B2O3-MgSO4-H2O was also evaporated and recorded to study the influence of boron concentration, pH, and electrolytes on the borate speciation in brine. The mononborates of B(OH)3 and B(OH)4- were found to be the only forms present in the original salt lake brine. Brine evaporation promotes the formation of polyborate anions B3O3(OH)4-, B5O6(OH)4-, and B6O7(OH)62- and also disappearance of the B(OH)4- ion in brine with boron concentration of more than 11 g/L in B2O3. The pentaborate ion of B5O6(OH)4- was sensitive to the solution pH and found to be appeared under the pH value of 8.0. While the hexaborate ion of B6O7(OH)62- was observed more dependent on the electrolyte of magnesium chloride due to its special properties, such as promoting boron accumulation, lowering solution pH, and also the strong af?nity for water molecules, which is beneficial to the polymerization of borate ions in brine. The interaction mechanisms among polyborate anions during evaporation had also been proposed.  相似文献   

Impact of evaporation on field capacity during water drainage redistribution in a soil     

Ali Aldrees  Amine Hafsi 《水文研究》2021,35(2):e14028

To this day, field capacity (FC) is rarely defined in the context of soil properties, and the use of non-physical simplistic models is the common way to normalize water content at FC. In this study, the problem of water drainage redistribution in a soil column with and without the presence of evaporation (EV) was extensively studied. Analytical solutions for the Richards equation were established for the case of water drainage redistribution through a deeply wetted soil water column with and without EV at FC conditions. Water retention and depth evolution curves were plotted first, using different EV values of (2 $\frac{\mathbf{mm}}{\mathbf{day}}$, 5 $\frac{\mathbf{mm}}{\mathbf{day}}$ and 8 $\frac{\mathbf{mm}}{\mathbf{day}}$) and second, for different drainage redistribution durations of (1 day, 4 days and 6 days) where EV was set to zero for the case with no EV or to a fixed value of 5 $\frac{\mathbf{mm}}{\mathbf{day}}$ for the case with EV. The results suggest that EV plays a significant role in soil water drainage suggesting that, in the presence of EV, the FC drying front reaches much higher depths in the soil water profile than if EV is turned off. It was also concluded that FC reaches deeper depths faster the stronger EV is acting at the surface of a soil water column. Additionally, the results suggest that the texture of the soil receiving drainage controls the amount of water available for EV and as a result, EV was found to play a stronger role the smaller the hydraulic conductivity of the soil is.  相似文献   

A new approach to estimate canopy evaporation and canopy interception capacity from evapotranspiration and sap flow measurements during and following wetting          下载免费PDF全文

J. Uddin  J. P. Foley  R. J. Smith  N. H. Hancock 《水文研究》2016,30(11):1757-1767

Canopy interception and its evaporation into the atmosphere during irrigation or a rainfall event are important in irrigation scheduling, but are challenging to estimate using conventional methods. This study introduces a new approach to estimate the canopy interception from measurements of actual total evapotranspiration (ET) using eddy covariance and estimation of the transpiration from measurements of sap flow. The measurements were conducted over a small‐scale sprinkler‐irrigated cotton field before, during and after sprinkler irrigation. Evaporation and sap flow dynamics during irrigation show that the total ET during irrigation increased significantly because of the evaporation of free intercepted water while transpiration was suppressed almost completely. The difference between actual ET and transpiration (sap flow) during and immediately following irrigation (post irrigation) represents the total canopy evaporation while the canopy interception capacity was calculated as the difference between actual ET and transpiration (sap flow) during drying (post irrigation) following cessation of the irrigation. The canopy evaporation of cotton canopy was calculated as 0.8 mm, and the interception capacity was estimated to be 0.31 mm of water. The measurement uncertainty in both the non‐dimensional ET and non‐dimensional sap flow was shown to be very low. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Effects of differing coverage of moss‐dominated soil crusts on hydrological processes and implications for disturbance in the Mu Us Sandland,China          下载免费PDF全文

Yongsheng Yang  Chongfeng Bu  Xingmin Mu  Kankan Zhang 《水文研究》2015,29(14):3112-3123

To study the effects of biological soil crusts (BSCs) on hydrological processes and their implications for disturbance in the Mu Us Sandland, the water infiltration, evaporation and soil moisture of high coverage (100% BSCs), middle coverage (40% BSCs) and low coverage (0% BSCs, bare sand) of moss‐dominated crusts were conducted in this study, respectively. The conclusions are as follows: (1) the main effects of moss‐dominated crusts in the Mu Us Sandland on the infiltration of rainwater were to reduce the infiltration depths and to retain the limited rainwater in shallow soil; (2) moss‐dominated crusts have no significant effects on daily evaporation when the volumetric water content at 4 cm depth in 100% BSCs (VWC4) was over 24.7%, on enhanced daily evaporation when the VWC4 ranged from 6.5% to 24.7% and on reduced daily evaporation when the VWC4 was less than 6.5%; and (3) decreasing the coverage of moss‐dominated crusts (from 100% to 40%) did not significantly change its effects on infiltration, evaporation and soil moisture. Our results demonstrated that for the growth and regeneration of shrubs, which were dominated by Artemisia ordosica in the Mu Us Sandland, high coverage of moss‐dominated crusts has negative effects on hydrological processes, and these negative effects could not be significantly reduced by decreasing the coverage of moss‐dominated crusts from 100% to 40%. Therefore, for the sustained and healthy development of shrub communities in the Mu Us Sandland, it is necessary to take appropriate measures for the well‐developed BSCs in the sites with high vegetation coverage in the rainy season. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Evaporation of perennial semi‐arid woodland in southeastern Australia is adapted for irregular but common dry periods          下载免费PDF全文

W. S. Meyer  E. Kondrlovà  G. R. Koerber 《水文研究》2015,29(17):3714-3726

Measurements of water vapour flux from semi‐arid perennial woodland (mallee) were made for 3 years using eddy covariance instrumentation. There have been no previous long‐term, detailed measures of water use in this ecosystem. Latent energy flux (LE) on a half hourly basis was the measure of the combined soil and plant evaporation, ‘evapotranspiration’ (E_LE) of the site. Aggregation over 3 years of the site measured rain (1136 mm) and the estimated evaporation (794 mm) suggests that 342 mm or 30% of rain had moved into or past the root zone of the vegetation. Above average rainfall during 2011 and the first quarter of 2012 (633 mm, 15 months) would likely have been the period during which significant groundwater recharge occurred. At times immediately after rainfall, E_LE rates were the same or exceeded estimates of potential E calculated from a suitably parameterized Penman–Monteith (E_PMo) equation. Apparent free water E from plant interception and soil evaporation was about 2.3 mm and lasted for 1.3 days following rainfall in summer, while in autumn, E was 5.1 mm that lasted over 5.4 days. The leaf area index (LAI) needed to adjust a wind function calibrated Penman equation (E_PMe) to match the E_LE values could be back calculated to generate seasonal change in LAI from 0.12 to 0.46 and compared well with normalized difference vegetation index; r = 0.38 and p = 0.0213* and LAI calculated from digital cover photography. The apparently conservative response of perennial vegetation evaporation to available water in these semi‐arid environments reinforces the conclusion that these ecosystems use this mechanism to survive the reasonably common dry periods. Plant response to soil water availability is primarily through gradual changes in leaf area. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Comparison of interception,forest floor evaporation and transpiration in Pinus radiata and Eucalyptus globulus plantations          下载免费PDF全文

R. G. Benyon  T. M. Doody 《水文研究》2015,29(6):1173-1187

Studies of evapotranspiration (ET) processes in forests often only measure one component of total ET, most commonly interception. This study examined all three components of annual ET (interception, evaporation from the forest floor and transpiration) and the correlations between them at 18 plantation forest sites in two species. All plantations had closed canopies, and sparse or no understorey. Single‐sided leaf area index averaged 3.5 (standard deviation ±0.5) in Eucalyptus globulus Labill. and 6.1 (±0.8) in Pinus radiata D.Don. Measurements included annual totals of rainfall in the open and under the canopy, stem flow (four sites only), evaporation from the forest floor and transpiration by the overstorey. Interception (I) averaged 19% (±4.9) of annual rainfall in E. globulus compared with 31% (±11.1) in P. radiata. However, higher annual interception in P. radiata did not result in higher total ET because annual evaporation from the forest floor (E) averaged 29% (±4.9) of rainfall in E. globulus but only 15% (±3.5) in P. radiata. Hence, the relative contribution of annual I plus E to ET did not differ significantly between the two species, averaging 48% (±7.3) of annual rainfall in E. globulus compared with 46% (±11.8) in P. radiata. As reported previously, transpiration did not differ significantly between the two species either, but was strongly related to depth‐to‐groundwater. In closed canopy plantations, mean annual ET did not differ between the two species. We conclude that when grown in plantations under similar soil and climatic conditions, conifer and broad‐leaved tree species can have similar annual ET, once the canopy of the plantation has closed. Lower average annual interception in broad‐leaved trees was offset by higher soil evaporation. These results highlight the importance of measuring all components of ET in studies of vegetation water use. Copyright © 2014 John Wiley & Sons, Ltd.  相似文献