The impacts of mountain pine beetle disturbance on the energy balance of snow during the melt period

Mountain snowpacks provide most of the annual discharge of western US rivers, but the future of water resources in the western USA is tenuous, as climatic changes have resulted in earlier spring melts that have exacerbated summer droughts. Compounding changes to the physical environment are biotic disturbances including that of the mountain pine beetle (MPB), which has decimated millions of acres of western North American forests. At the watershed scale, MPB disturbance increases the peak hydrograph, and at the stand scale, the ‘grey’ phase of MPB canopy disturbance decreases canopy snow interception, increases snow albedo, increases net shortwave radiation, and decreases net longwave radiation versus the ‘red’ phase. Fewer studies have been conducted on the red phase of MPB disturbance and in the mixed coniferous stands that may follow MPB‐damaged forests. We measured the energy balance of four snowpacks representing different stages of MPB damage, management, and recovery: a lodgepole pine stand, an MPB‐infested stand in the red phase, a mixed coniferous stand (representing one successional trajectory), and a clear‐cut (representing reactive management) in the Tenderfoot Creek Experimental Forest in Montana, USA. Net longwave radiation was lower in the MPB‐infested stand despite higher basal area and plant area index of the other forests, suggesting that the desiccated needles serve as a less effective thermal buffer against longwave radiative losses. Eddy covariance observations of sensible and latent heat flux indicate that they are of similar but opposite magnitude, on the order of 20 MJ m^?2 during the melt period. Further analyses reveal that net turbulent energy fluxes were near zero because of the temperature and atmospheric vapour pressure encountered during the melt period. Future research should place snow science in the context of forest succession and management and address important uncertainties regarding the timing and magnitude of needlefall events. Copyright © 2015 John Wiley & Sons, Ltd.     

Energy partitioning over a semi‐arid shrubland in northern China

During the last decade, the widely distributed shrublands in northern China have shown significant signs of recovery from desertification, the result of widespread conservation practices. However, to support the current efforts in conservation, more knowledge is needed on surface energy partitioning and its biophysical controls. Using eddy‐covariance measurements made over a semi‐arid shrubland in northwest China in 2012, we examined how surface energy‐balance components vary on diurnal and seasonal scales, and how biophysical factors control bulk surface parameters and energy exchange. Sensible heat flux (H) exceeded latent heat flux (λE) during most of the year, resulting in an annual Bowen ratio (β, i.e. H/λE) of 2.0. λE exceeded H only in mid‐summer when frequent rainfall co‐occurred with the seasonal peak in leaf area index (LAI). Evapotranspiration reached a daily maximum of 3.3 mm day^?1, and summed to 283 mm yr^?1. The evaporative fraction (EF, i.e. λE/R_n), Priestley–Taylor coefficient (α), surface conductance (g_s) and decoupling coefficient (Ω) were all positively correlated with soil water content (SWC) and LAI. The direct enhancement of λE by high vapour pressure deficit (VPD) was buffered by a concurrent suppression of g_s. The g_s played a direct role in controlling EF and α by mediating the effects of LAI, SWC and VPD. Our results highlight the importance of adaptive plant responses to water scarcity in regulating ecosystem energy partitioning, and suggest an important role for revegetation in the reversal of desertification in semi‐arid areas. Copyright © 2015 John Wiley & Sons, Ltd.     

北京大学陆面过程模式PKULM(Peking University Land Model)介绍及检验

陆面过程模式是气候模式和天气模式的核心组成部分之一.在土壤-植被-大气耦合模式(Soil-Plant-Atmosphere Model, SPAM)的基础上,发展了新一代北京大学陆面过程模式PKULM(Peking University Land Model).本文首先介绍了PKULM的辐射传输、湍流输送、光合作用、土壤水热输送等过程的参数化方案;采用隐式迭代计算框架,发展并应用了一个快速的线性方程组求解算法,提高了模式计算稳定性;提出并使用了二分搜索算法计算气孔阻抗,避免了CLM(Community Land Model)等使用的迭代方法在干旱区不稳定的情况,提高了模式的适用性;采用水势为基础的土壤水分扩散方程,使模式能够模拟土壤饱和区的水分输送过程,为进一步与水文过程模式耦合奠定了基础;还发展了一个地表积水与径流过程的机理模型,提高了模式对地表水分平衡过程的模拟能力;最后,使用"中国西北干旱区陆-气相互作用观测试验"平凉站的资料对模式进行了检验并与NOAH(National Center for Environmental Prediction, Oregon State University, Air Force, and Hydrology Lab model)陆面过程模式的模拟结果进行了比较,结果表明PKULM能够较好地模拟西北半干旱区农田下垫面地气交换过程.     

21世纪中国煤地质与勘探展望

中国煤炭资源量49000余亿t,实际探明储量6000余亿t,其中可供建并使用的精查储量390亿t。由于油气资源有限,加上近年煤炭在降低成本。减少污染方面取得进展,21世纪初可望成为廉价、洁净和可靠的能源,在能源构成中重居领先地位。煤炭在中国化石能源资源中约占95％,在能源构成中将长期占据主导地位。煤田地质工作直加速东部勘探,突出西部找水,提高勘探程度和煤矿地质研究精度,为煤炭开发、洁净煤技术提供可靠信息。     

2010年4月14日青海玉树7.1级地震序列中小地震辐射能量的估计

本文利用震后架设的4个流动台站和震源区周围3个固定台站记录到的青海玉树7.1级地震序列波形资料,资料时间截止到2010年5月19日.经过传播路径效应和场地响应校正后,估算了玉树地震序列中80个中小地震的辐射能量.比较了辐射能量估计中不同方法之间结果存在的差异性,首次考虑了由于仪器频带宽度的限制而造成的中小地震辐射能量的低估与补偿问题,得到以下主要结论:(1)分别采用Andrews方法、震源实际谱方法(区分能量补偿前和后二种情况)和根据理论模型并将积分上限外推到所计算地震拐角频率的10倍的方法(理论谱方法)计算出的中小地震辐射能量4种结果基本上位于同一个量级水平之上,表明结果具有一定的可靠性和稳定性.这其中,Andrews方法得到的辐射能量最低,理论谱方法得到的结果最高,而由实际谱方法得到的地震辐射能量介于两者之间.(2)由古登堡经验公式得到的地震辐射能量远高于上述4种方法计算出的结果,能够达到理论谱方法结果的4倍,而且随震级的增大,由它带来的辐射能量的高估趋势更加明显.(3)由于没有考虑地震能量的补偿,Andrews方法得到的地震辐射量明显偏低.用两种不同方法进行地震辐射能量补偿后得到的结果比较接近,但考虑到仪器频带上限值设定的复杂性,认为由理论谱方法计算中小地震的辐射能量更加合适.(4)经过能量补偿后地震辐射能量要高于未作能量补偿的结果,能量补偿带来的辐射能量增加的作用对于小地震更加明显.在本文研究范围之内,不同方法得到的折合能量均明显存在随地震矩的增大而增大的现象,反映出玉树余震序列中大震地震辐射效率高于小震.     

青藏高原东南缘活动断裂的地震应变能释放系统研究

本文以青藏高原东南缘为研究区域,利用G-R震级能量经验公式和Benioff地震应变能释放曲线,对该区域内1500年以来的历史地震应变能释放进行了系统性的研究。文中给出了各断裂带和断块区的地震应变能释放周期表,及相应的地震危险性。分析发现研究区域地震应变能的释放具有东强西弱,南强北弱的特征,整体上各断层断块区的历史地震应变能释放符合准周期模式,某些断层和断块区上的地震周期具有某种程度上的同步现象。青藏高原东南缘现今处于大释放期中,地震的危险性不能忽视。局部结果显示,安宁河-则木河断裂带、小江断裂带的危险性很高,对于这些危险区要重点跟踪研究。今后仍需结合不同研究方法来提高地震危险性评估的可靠性。     

新型装配式混凝土框架连接节点抗震性能试验

为推广装配式混凝土框架结构的应用,提出3种不同的新型装配式钢筋混凝土框架中节点连接形式,进行低周往复荷载试验。对比各试件的破坏形态、滞回性能、刚度退化、累积耗能和节点剪切变形等抗震指标。研究结果表明:采用方钢管连接的装配式混凝土节点呈现梁端弯曲破坏,采用工字钢连接或对拉螺栓连接的节点呈现节点核心区剪切破坏。采用方钢管的连接形式既能改善节点核心区的破坏形态,又能提高其承载能力、变形能力、耗能能力和梁端转动能力,同时显著改善节点的滞回特性,减小核心区的剪切变形。在弹塑性和塑性变形阶段,采用方钢管连接形式的装配式混凝土节点的抗震性能优于工字钢连接和对拉螺栓连接的节点。此外,采用工字钢连接形式比对拉螺栓连接形式的节点具有更高的承载能力、耗能能力和较小的核心区剪切变形。     

建筑围护结构节能与防火体系构建

从围护结构节能与防火一体化思路出发,提倡钢筋混凝土结构保温一体化建筑体系和砌体结构保温一体化建筑体系;尤其主张在我国建筑工业化全面升级的基础上大力开发与推广保温型混凝土预制装配化技术,统一建筑模数,实现标准化与多样化;针对预制装配化保温型混凝土在梁、构造柱等容易出现的冷、热桥问题的部位,创新式提出以相变储能材料与建筑结构相融合来提高建这些部位的热工性能,减少温度梯度;从系统上做到保温与建筑同寿命、免维护、工序少,工期短、耐火等,从而真正实现低碳,构建建筑围护结构节能防火一体化建筑体系。