Plant drought tolerance trait is the key parameter in improving the modeling of terrestrial transpiration in arid and semi-arid regions   总被引：1，自引：0，他引：1       下载免费PDF全文

Xintao Liu  Xingjie Lu  Shulei Zhang  Zhongwang Wei  Nan Wei  Shupeng Zhang  Hua Yuan  Wei Shangguan  Shaofeng Liu  Jianfeng Huang  Lu Li  Xiulan Ye  Jinxuan Zhou  Wenke Hu  Yongjiu Dai 《大气和海洋科学快报》2022,15(1):35-41

陆面过程蒸腾作用的模拟制约着天气,气候降水预测的精确度.近几十年来,为了更好地描述植被蒸腾的水力约束,陆面过程模式发展了基于植物性状的植物水力胁迫方案.然而,我们对于植物性状在蒸腾模拟中的地位仍然缺乏了解,植物性状对蒸腾的重要性仍需进一步量化.本研究利用Morris方法评估植物性状参数在通用陆面模式植物水力胁迫方案(CoLM-P₅₀HS)中的重要性,针对17种植物性状,筛选出最为重要的:耐旱性状(P₅₀),气孔性状,和光合作用性状.在12个FLUXNET站点中,参数的重要性由归一化敏感度来衡量.P₅₀的重要性随着降水的减少而增加,而气孔性状和光合作用性状的重要性则随着降水的减少而减少.在干旱或半干旱地区,P₅₀比气孔性状和光合作用性状更重要,这意味着当植物经常经历干旱时,水力安全策略比植物生长策略更关键.而耐旱性状的巨大变异性进一步暗示了多种植物水力安全策略的共存.忽视P₅₀的变异性可能会对陆面过程模式蒸腾作用的模拟造成严重误差.因此,为了更好地表示植物水力功能的变异性,需要增加对耐旱性状的观测并耦合到陆面模式中.  相似文献   

Interpreting Reynolds stress from perspective of eddy geometry     

《Dynamics of Atmospheres and Oceans》2021

Geometric features in oceanic mesoscale eddies such as tilt and anisotropy can influence the properties of the Reynolds stress that provides feedback between the eddies and the background flow. By regarding an eddy as a wave, previous studies have parameterized the Reynolds stress based on the equivalence in the tilt angle between the phase of the eddy stream functions and the variance ellipse for the Reynolds stress (RS-ellipse). However, the wave assumption cannot predict the anisotropy of the RS-ellipse, and also largely simplifies the eddy geometry, which would naturally be an ellipsoid rather than a wave. The present study explores the shape relation between elliptical eddies and the RS-ellipse, by mathematically reformulating the Reynolds stress based on the eddy shape. The new formula reveals that the shape relation is regulated by the horizontal extent of the occurrence probability distribution (PDF) of the eddy, and that the shape of the eddy and RS-ellipse are identical at the place of maximum PDF when the horizontal scale of the PDF is sufficiently larger than the size of the eddy. A similar tendency is found in eddies detected by satellite altimetry in the Kuroshio Extension jet region. A detailed analysis of the PDF in this region shows that the tilts of the eddies are likely to be consistent with the destabilization effect on the jet, suggesting a strong relation between the eddy geometry and the jet's stability in this region. These findings may open a path toward a new method to parameterize the Reynolds stress with the background state, exploiting the shape equivalence between the eddies and the RS-ellipse.  相似文献   

台风利奇马登陆期间的对流结构特征及对强降雨影响     

陈涛  董林  罗玲  杨舒楠 《气象》2021,47(12):1433-1443

2019年9号台风利奇马在浙江造成极端降水,其中8月9日白天浙江东部受台风外围螺旋雨带长时间影响,9日夜间在台风内核对流影响下降水有显著增强;降水中心与浙江临海地区的天台山、括苍山和雁荡山等地形特征密切相关。GPM（Global Precipitation Measure）卫星遥感反演表明近岸台风螺旋雨带以层积混合型降水为主,台风眼墙区域以热带暖云对流型降水为主;眼墙区雨滴有效直径更大、雨滴数密度更高,有利于形成高降水强度。台风登陆前移动速度较慢,浙江沿海地区维持低层锋生和辐合,有利于外围螺旋雨带降水维持和增强;登陆前后受环境垂直切变等因素影响,台风中心左前侧眼墙区域对流活跃,在登陆点附近强降水区偏向于台风中心左侧。分钟级降水观测表明台风登陆期间浙江近海山区降水强度2~3倍于平原地区,其中地形性降水增幅效应与台风对流非对称结构差异对降水影响程度基本相当,有利于在台风中心左前侧的括苍山—雁荡山山区形成强降水中心。  相似文献   

Climatology of Shear Line and Related Rainstorm over the Southern Yangtze River Valley Based on an Improved Intelligent Identification Method     

刘金卿  陈鹤  徐靖宇 《热带气象学报(英文版)》2022,28(4):413-424

Based on four reanalysis datasets including CMA-RA, ERA5, ERA-Interim, and FNL, this paper proposes an improved intelligent method for shear line identification by introducing a second-order zonal-wind shear. Climatic characteristics of shear lines and related rainstorms over the Southern Yangtze River Valley (SYRV) during the summers (June-August) from 2008 to 2018 are then analyzed by using two types of unsupervised machine learning algorithm, namely the t-distributed stochastic neighbor embedding method (t-SNE) and the k-means clustering method. The results are as follows: (1) The reproducibility of the 850 hPa wind fields over the SYRV using China’s reanalysis product CMA-RA is superior to that of European and American products including ERA5, ERA-Interim, and FNL. (2) Theory and observations indicate that the introduction of a second-order zonal-wind shear criterion can effectively eliminate the continuous cyclonic curvature of the wind field and identify shear lines with significant discontinuities. (3) The occurrence frequency of shear lines appearing in the daytime and nighttime is almost equal, but the intensity and the accompanying rainstorm have a clear diurnal variation: they are significantly stronger during daytime than those at nighttime. (4) Half (47%) of the shear lines can cause short-duration rainstorms (≥20 mm (3h)-1 ), and shear line rainstorms account for one-sixth (16%) of the total summer short-duration rainstorms. Rainstorms caused by shear lines are significantly stronger than that caused by other synoptic forcing. (5) Under the influence of stronger water vapor transport and barotropic instability, shear lines and related rainstorms in the north and middle of the SYRV are stronger than those in the south.  相似文献   

Implications of turbulent shear on clay floc break-up along the Atlantic estuary (Bouregreg), Morocco     

Krishnamoorthy Lakshmi Ammal Priya  Soufiane Haddout  Joan Cecilia Catubig Casila 《国际泥沙研究》2022,37(2):248-257

Water depth,salinity,current,and suspended sediment concentration(SSC)were measured along with the grain size distribution of bed sediment along an estuarine longitudinal section.The floc size increased with increase in the percentage of clay and silt,while decreased with increase in the percentage of sand content of bed sediment.The turbulent shear,G,had a direct effect on floc size with its value increasing with increase in G up to a G value of 15 s^-1,while an inverse relation existed between floc size and G at higher G(G>15 s^-1).Further,higher turbulence enabled sand to get resuspended and cause additional shear leading to the break-up of flocs.An attempt was made to modify G to account for the combined effect of water turbulence(G)and shear imparted by sand(Ga)and the impact of the modification of G on the predictability of floc size was evaluated.A new model was developed which explains floc size in terms of sediment concentration(C),salinity gradient(S),and G for different scenarios based on the value of G.Sensitivity analysis was done for observed floc size(FS)and predicted floc size using four approaches:(I)FSαC^x;(II)FSαC^xS-y;(III)FSαC^xS^-yGz for G<15 s^-1and FSαC^xS^-yG-z for G>15 s^-1;and(IV)FSαC^xS^-yG_m^-zfor G>15 s^-1and G_m=G+Ga,where x,y,and z are determined by calibration.It was observed that the predictability of the floc size improved when the turbulence was modified to account for shear imparted by sand so that the coefficient of determination was increased from 0.78 for model III to 0.89 for model IV.Further,the settling velocity was expressed as a function of suspended sediment concentration,turbulent shear,and salinity gradient.The predictability of settling velocity was improved(R2 increased from 0.77 to 0.86)when the additional turbulence created by sand was incorporated in the non-dimensional empirical equation.The study highlights the influence of sand in causing the break-up of flocs and suggests that for turbulence shear values high enough to resuspend sand,and G has to be modified to account for the additional shear imparted by sand in mixed sediment estuarine environments.  相似文献   

张家口—渤海地震带岩石圈磁场时空变化特征     

张海洋  李博  苏树朋  王朝景  刘德强  赵慧琴  毛丰龙 《地震》2022,42(1):133-144

利用2016—2018年3期华北地区流动地磁矢量原始测量资料, 经数据计算获得2期华北地区和张家口—渤海地震活动带及邻区岩石圈磁场时空变化模型。 研究结果显示: 张家口—渤海地震带岩石圈磁场变化空间分布不均匀, 具有明显的分区特征, 在张家口段(西段)与北京段(中西段)分界处和北京段(中西段)与唐山段(中东段)分界处岩石圈磁场各要素具有明显的异常变化, 如水平矢量存在转向和幅值变化, 磁偏角与磁倾角具有正负异常高梯度带的特征, 这与张家口—渤海地震带构造分段性特征密切相关。 张家口—渤海地震带位于燕山块体与华北平原块体之间, 两者运动的平动速率之差是张家口—渤海地震带左旋走滑的直接动力来源, 而各断裂带左旋走滑速率之差很可能是岩石圈磁场空间变化分段性分布的主要原因。  相似文献   

板钉连接CFST柱-RC梁节点梁端塑性铰区受力性能数值模拟     

马华  阚吉平  赵玉坤  李振宝 《震灾防御技术》2022,17(2):381-391

建立竖板-栓钉连接钢管混凝土（CFST）柱-钢筋混凝土（RC）梁节点试件（SSJD）拟静力加载试验有限元模型,并在节点损伤情况、梁端荷载-位移曲线等数值模拟结果与试验结果吻合较好的基础上,进一步开展了RC梁混凝土强度、配筋率ρ_s和连接竖板长度L_b及界面连接情况等对CFST柱-RC梁节点梁端塑性铰区域力学性能的影响。研究结果表明,RC梁混凝土强度对试件SSJD塑性铰区域受力性能的影响较小;适筋范围内RC梁配筋率增加可适当提高试件SSJD承载力和延性;随着连接竖板长度的增加,梁端塑性铰区域外移,梁破坏荷载增大;本研究给出的RC梁与CFST柱之间的界面抗剪承载力模拟值与计算值吻合较好,可用于界面抗剪设计。  相似文献   

Experimental study on the dynamic modulus of compacted loess under bidirectional dynamic load     

Liguo Yang  Shengjun Shao  Qilong Sun  Ping Wang 《地震研究进展（英文）》2022,2(3):100115

The dynamic characteristics of compacted loess are of great significance to the seismic construction of the Loess Plateau area in Northwest China, where earthquakes frequently occur. To study the change in the dynamic modulus of the foundation soil under the combined action of vertical and horizontal earthquakes, a hollow cylindrical torsion shear instrument capable of vibrating in four directions was used to perform two-way coupling of compression and torsion of Xi'an compacted loess under different dry density and deviator stress ratios. The results show that increasing the dry density can improve the initial dynamic compression modulus and initial dynamic shear modulus of compacted loess. With an increase in the deviator stress ratio, the initial dynamic compression modulus increases, to a certain extent, but the initial dynamic shear modulus decreases slightly. The dynamic modulus gradually decreases with the development of dynamic strain and tends to be stable, and the dynamic modulus that reaches the same strain increases with an increasing dry density. At the initial stage of dynamic loading, the attenuation of the dynamic shear modulus with the strain development is faster than that of the dynamic compression modulus. Compared with previous research results, it is determined that the dynamic modulus of loess under bidirectional dynamic loading is lower and the attenuation rate is faster than that under single-direction dynamic loading. The deviator stress ratio has a more obvious effect on the dynamic compression modulus. The increase in the deviator stress ratio can increase the dynamic compression modulus, to a certain extent. However, the deviator stress ratio has almost no effect on the dynamic shear modulus, and can therefore be ignored.  相似文献   

竖波钢板组合剪力墙震损修复研究          下载免费PDF全文

王威  赵昊田  权超超  宋鸿来  李昱  周毅香 《世界地震工程》2022,38(2):067-79

钢板组合剪力墙在强震作用下受损严重,震损修复问题较为突出。现设计一片以方钢管作为边缘约束构件的竖波钢板组合剪力墙,在最大弹塑性层间位移角时的震损情况进行分析:竖波钢板组合剪力墙边缘约束方钢管刚度较大,与墙体不匹配,最终发生方钢管从地梁拔动的脆性破坏模式。对竖波钢板组合剪力墙进行震损修复,得到墙趾可更换竖波钢板组合剪力墙,然后进行拟静力试验。试验结果表明:（1）在震损后的竖波钢板组合剪力墙的墙趾处安装阻尼器,其抗震性能基本得到恢复。（2）修复后的竖波钢板组合剪力墙承载力较修复前降低了23%,但延性和耗能能力显著提升。（3）改变了竖波钢板组合剪力墙的破坏模式,由脆性破坏转化为延性破坏。借助有限元软件详细讨论了内嵌竖向波形钢板厚度和波角、轴压比、阻尼器腹板数量对修复后竖波钢板组合剪力墙抗剪承载力的影响,结果表明:改变内嵌竖向波形钢板厚度对试件抗剪承载力影响较大,而改变内嵌竖向波形钢板波角、轴压比和阻尼器腹板数量对试件抗剪承载力影响较小。结合有限元算例,提出修复后竖波钢板组合剪力墙抗剪承载力的计算公式,可为工程实际提供参考。  相似文献   

型钢连接装配式低矮剪力墙抗震性能试验研究          下载免费PDF全文

吴志平  王丹  胡大柱  王增  严琦  赵娟 《世界地震工程》2022,38(4):054-64

采用带锚筋的锚板、腹板、端板以及加劲板作为连接件,能够通过干式连接方法将上下预制剪力墙构件连为整体。为研究该新型全装配式剪力墙的受力性能和抗震性能,设计了2个剪跨比为0.783的试件和1个相同剪跨比及配筋率的现浇整体墙体,并进行了低周往复拟静力试验,分析了该全装配式剪力墙的承载能力、刚度、延性性能和耗能能力等。研究结果表明:现浇整体墙体和全装配式剪力墙的破坏形式均为受剪破坏,全装配式剪力墙的极限位移角大于现浇整体墙体极限位移角,分别为1/77和1/133,轴压比为0.3时平均延性系数3.47,低于现浇整体墙体平均延性系数4.62;但该全装配式剪力墙具有较高的承载能力和耗能能力。型钢与剪力墙的锚筋需采用穿孔塞焊的形式连接,避免锚筋与锚板焊接的位置发生剪断的现象。  相似文献