A field‐based parameterization of wind flow recovery in the lee of dryland plants

Wind erosion is a key component of land degradation in vulnerable dryland regions. Despite a wealth of studies investigating the impact of vegetation and windbreaks on windflow in controlled wind‐tunnel and modelling environments, there is still a paucity of empirical field data for accurately parameterizing the effect of vegetation in wind and sediment transport models. The aim of this study is to present a general parameterization of wind flow recovery in the lee of typical dryland vegetation elements (grass clumps and shrubs), based on their height (h ) and optical porosity (θ ). Spatial variations in mean wind velocity around eight isolated vegetation elements in Namibia (three grass clumps and five shrubs) were recorded at 0.30 m height, using a combination of sonic and cup anemometry sampled at a temporal frequency of 10 seconds. Wind flow recovery in the lee of the elements was parameterized in an exponential form, . The best‐fit parameters derived from the field data were u ₀ = u _ref(0.0146θ ? 0.4076) and b = 0.0105θ + 0.1627 . By comparing this parameterization to existing models, it is shown that wind recovery curves derived from two‐dimensional wind fence experiments may not be suitable analogues for describing airflow around more complex, three‐dimensional forms. Field‐derived parameterizations such as the one presented here are a crucial step for connecting plant‐scale windflow behaviour to dryland bedform development at landscape scales. © 2016 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.     

The CREp program and the ICE-D production rate calibration database: A fully parameterizable and updated online tool to compute cosmic-ray exposure ages

Over the last decades, cosmogenic exposure dating has permitted major advances in many fields of Earth surface sciences and particularly in paleoglaciology. Yet, exposure age calculation remains a complicated and dense procedure. It requires numerous choices of parameterization and the use of an accurate production rate.This study describes the CREp program (http://crep.crpg.cnrs-nancy.fr) and the ICE-D production rate online database (http://calibration.ice-d.org). This system is designed so that the CREp calculator will automatically reflect the current state of this global calibration database production rate, ICE-D. ICE-D will be regularly updated in order to incorporate new calibration data and reflect the current state of the available literature.CREp is a Octave/Matlab^© online code that computes Cosmic Ray Exposure (CRE) ages for ³He and ¹⁰Be. A stand-alone version of the CREp code is also released with the present article. Note however that only the online version is connected to the online database ICE-D. The CREp program offers the possibility to calculate ages with two scaling models: i.e. the empirical Lal-Stone time-dependent model (Balco et al., 2008; Lal, 1991; Stone, 2000) with the muon parameters of Braucher et al. (2011), and the Lifton-Sato-Dunai (LSD) theoretical model (Lifton et al., 2014). The default atmosphere model is the ERA-40 database (Uppala et al., 2005), but one may also use the standard atmosphere for comparison (N.O.A.A, 1976). To perform the time-dependent correction, users may import their own geomagnetic database for paleomagnetic corrections or opt for one of the three proposed datasets (Lifton, 2016; Lifton et al., 2014; Muscheler et al., 2005).For the important choice of the production rate, CREp is linked to a database of production rate calibration data that is part of the ICE-D (Informal Cosmogenic-nuclide Exposure-age Database) project (http://calibration.ice-d.org). This database includes published empirical calibration rate studies that are publicly available at present, comprising those of the CRONUS-Earth and CRONUS-EU projects, as well as studies from other projects. In the present study, the efficacy of the different scaling models has also been evaluated looking at the statistical dispersion of the computed Sea Level High Latitude (SLHL) production rates. Lal/Stone and LSD models have comparable efficacies, and the impact of the tested atmospheric model and the geomagnetic database is also limited.Users however have several possibilities to select the production rate: 1) using a worldwide mean value, 2) a regionally averaged value (not available in regions with no data), 3) a local unique value, which can be chosen among the existing dataset or imported by the user, or 4) any combination of multiple calibration data.If a global mean is chosen, the 1σ uncertainty arising from the production rate is about 5% for ¹⁰Be and 10% for ³He. If a regional production rate is picked, these uncertainties are potentially lower.CREp is able to calculate a large number of ages in a reasonable time (typically < 30 s for 50 samples). The user may export a summary table of the computed ages and the density probability function associated with each age (in the form of a spreadsheet).     

2016年门源6.4级、杂多6.2级地震前热红外辐射变化特征

2016年青海省发生门源6.4级和杂多6.2级地震,针对2次6级以上地震发生前热红外数据变化特征进行分析,研究发现:门源6.4级和杂多6.2级地震前热红外辐射增强变化应为地震异常;2次地震映震结果对比表明,频段1、4和5为优势映震频段,异常幅度为年均值4.5倍左右可作为地震异常判断依据。     

Fourier transform infrared microspectroscopic characterization of Neoproterozoic organic microfossils from the Fifteenmile Group in Yukon,Canada

Conventional and synchrotron radiation‐based (SR) Fourier transform infrared microspectroscopies (micro‐FTIR) were applied to four types of ~ 810 Ma organic‐walled microfossils together with diffuse organic matter (OM) and one irregularly shaped structure from the Fifteenmile Group, in Yukon, Canada, for their chemical characterization. The microfossils comprised one filamentous type and three coccoidal types. Micro‐FTIR mapping analysis revealed the micrometer‐scale, spatial distribution of organic components (aliphatic C‐H bonds) and carbonate in the microfossils. Based on comparisons of CH₃/CH₂ peak height ratios (R_3/2) and morphologies of the microfossils (without the diffuse OM) to those of previously described Proterozoic microfossils, possible affinities of the microfossils are suggested, as follows. Palaeolyngbya? and Glenobotrydion belong to bacteria. Myxococcoides is not clearly characterized due to the significant mixing with diffuse OM containing abundant aliphatic C‐H groups. The irregularly shaped structure may represent a eukaryote. The diffuse OM may represent a mixture of decomposed microbial cells and extracellular polymeric substances (EPS). SR micro‐FTIR measurements of two coccoid types (Glenobotrydion and Unnamed Coccoid Form D) revealed that the R_3/2 values of the internal spots with wall structures are similar to those without wall structures in Glenobotrydion: those values from Unnamed Coccoid Form D were different. The results suggest that these two coccoids are different chemically as well as morphologically. Micro‐FTIR characterization of the organic‐walled microfossils together with morphological analysis provides new insight into their biological affinities.     

北斗卫星太阳光压解析模型建立及应用

光压模型是导航卫星高精度定轨、定位的基础。目前关于北斗卫星光压摄动模型的研究并不少见,但基于卫星物理参数的综合解析模型建立与应用公开可见的论述并不多见。不同于其他保守和非保守摄动力,光压辐射与卫星本身参数状态密切相关,具有明显的个体差异性。本文基于光压辐射的物理机理、北斗卫星物理参数、姿态控制模式等,建立光压摄动综合解析模型,以精密星历和激光测距数据为基准,验证了综合解析模型能够获得分米级的精密定轨精度。在此基础上,根据卫星角动量守恒和在轨遥测参数变化,分析了综合解析模型和在轨实际干扰力的差值,提出了在综合解析模型基础上增加常数经验修正项Da、Ya的方法,以北斗C08、C10星为例,分别可获得0.078、0.084 m的SLR检核精度,相比于利用CODE经验改进模型,精度分别提高0.021、0.045 m。     

多云条件有利于亚热带人工针叶林不同季节净生态系统碳吸收（英文）

太阳辐射的动态变化对生态系统固碳有重要影响,而不同天气条件下太阳辐射的改变对森林净生态系统碳交换(NEE)的影响还不明确。本研究利用亚热带人工针叶林生态系统2012年的通量数据和气象数据,分析了晴天、多云、阴天三种天气对NEE的影响。基于一年数据的研究结果表明:在不同季节中,不同天气下光响应曲线的变化没有季节性差异。和晴天条件相比,多云条件下的表观量子效率(?),150和750 W m^–2光强下的潜在光合速率(P₁₅₀和P₇₅₀)分别平均提高了82.3%、217.7%、22.5%;阴天条件下的α和P₁₅₀分别平均提高了118.5%和301%。中等辐射条件有利于NEE达到最大值,但低辐射条件对NEE有抑制作用。在大多数情况下,与晴天相比,多云下NEE的相对改变量(%NEE)为正,但阴天下为负。多云条件下最大%NEE的平均值在春夏秋冬分别为42.4%、34.1%、1.6%、-87.3%。本研究表明多云天气促进亚热带人工针叶林的潜在光合速率和NEE。     

不同参数化方案试验对南黄海典型台风中心最低气压和最大风速数值模拟影响

为提高对南黄海典型台风的中心最低气压及其最大风速的预报能力,本文以经过南黄海的典型台风——2011年09号台风"梅花"以及2015年09号台风"灿鸿"为例,基于WRF中尺度数值预报模式,以欧洲中期天气预报中心(ECWMF)的再分析资料作为模式的初始场以及侧边界条件,对南黄海台风数值模拟进行了分析。结果表明,不同微物理方案的选择对南黄海典型台风中心最低气压和最大风速模拟结果影响较小;YSU边界层方案以及KF积云对流方案组合模拟效果最佳,可使南黄海典型台风中心最低气压和最大风速的模拟结果误差最小。     

发展几何光学遥感建模理论，推动定量遥感科学前行——深切缅怀李小文院士

李小文长期致力于遥感基础研究,是植被几何光学遥感建模的先驱。他创建了Li-Strahler几何光学模型,论文入选"国际光学工程学会(SPIE)"里程碑系列文集。以李小文为首席科学家,带领国内外科学团队,在植被二向性反射建模、热红外遥感辐射方向性建模、遥感信息尺度效应、定量遥感综合实验与真实性检验方面做出了卓越成就。本文总结了李小文的主要学术思想,对定量遥感相关研究进展进行了总结和回顾,对遥感科学及相关领域具有重要的借鉴和参考意义。     

近红外偏振辐射卫星数据的海洋耀光动态检测

太阳光入射海表特定区域形成海洋耀光,呈强反射和偏振特性。在卫星海洋遥感中,海洋耀光对遥感成像质量有较大影响,尤其对海洋上空云、气溶胶及海色等研究干扰较大,因此剔除海洋耀光是卫星遥感数据处理过程中首先要解决的重要问题。以PARASOL卫星的POLDER3载荷数据为研究对象,获取载荷成像时刻太阳及观测几何、海表风速风向及气溶胶光学厚度等参数,采用海气辐射传输相关理论,结合耀光角和多角度NIR偏振辐射信息(865 nm),构建基于近红外偏振辐射特性规则的OGDD模型,获取耀光角临界值实现耀光动态检测。以印度洋某海区为研究对象,获取实测耀光区NIR通道的大气层顶反射率和偏振反射率,利用OGDD模型将耀光角判别临界值调整为34°。相比MODIS经验临界值(40°),标记耀光像元相对减少了30%。结果表明,该方法不仅能通过动态调整临界值准确识别海洋耀光,为云检测及云物理特性反演提供可靠的源数据,还能为高分五号卫星多角度偏振载荷在轨定标及气溶胶反演提供支持。     

Numerical study of three-dimensional wave-induced longshore current's effects on sediment spreading of the Huanghe River mouth

A three-dimensional wave radiation stress is introduced into the hydrodynamic sediment coupled model COHERENS-SED, which has been developed through introducing wave-enhanced bottom shear stress, wave dependent surface drag coefficient, wave-induced surface mixing, SWAN, damping function of sediment on turbulence, sediment model and depth-dependent wave radiation stress to COHERENS. The COHERENS-SED is adopted to study the effects induced by wave-induced three-dimensional longshore current on suspended sediment spreading of the Huanghe River (Yellow River) mouth. Several different cases divided by setting different wave parameters of inputting boundary waves are carried out. The modeling results agree with measurement data. In terms of simulation results, it is easy to know that three-dimensional wave radiation stress plays an obvious role when inputting boundary wave height is stronger than 3 m. Moreover, wave direction also affects the sediment spreading rules of the mouth strongly too.