Effects of Averaging Period on Energy Fluxes and the Energy-Balance Ratio as Measured with an Eddy-Covariance System

The eddy-covariance method is an important technique for investigating the exchange of energy and substances between the atmosphere and an ecosystem. However, an inappropriate averaging period leads to inaccurate fluxes and a low energy-balance ratio (EBR). The effects of various averaging periods on fluxes and the EBR are analyzed using flux data from the entire growth stage of maize measured with an eddy-covariance system in northern China. We find that the relative error of the flux between an averaging period of 10–60 min and the commonly used averaging period of 30 min is within 3%. When the averaging period is between 10 and 60 min, the magnitudes of fluxes increase with the length of the averaging period at various growth stages. For averaging periods exceeding 60 min, the magnitudes of fluxes vary significantly, particularly for periods longer than 120 min. In general, \({ EBR} > 0.8\) in the maize field, tending to increase within periods of 10–60 min, but decreasing rapidly at various growth stages for averaging periods longer than 120 min. Ogive functions indicate an optimal averaging period of the seedling–shooting and shooting–heading stages is approximately 10–30 min, and that of the heading–filling and filling–maturity stages is 30–60 min.     

Linkages between the North Pacific Oscillation and central tropical Pacific SSTs at low frequencies

The North Pacific Oscillation (NPO) recently (re-)emerged in the literature as a key atmospheric mode in Northern Hemisphere climate variability, especially in the Pacific sector. Defined as a dipole of sea level pressure (SLP) between, roughly, Alaska and Hawaii, the NPO is connected with downstream weather conditions over North America, serves as the atmospheric forcing pattern of the North Pacific Gyre Oscillation (NPGO), and is a potential mechanism linking extratropical atmospheric variability to El Ni?o events in the tropical Pacific. This paper explores further the forcing dynamics of the NPO and, in particular, that of its individual poles. Using observational data and experiments with a simple atmospheric general circulation model (AGCM), we illustrate that the southern pole of the NPO (i.e., the one near Hawaii) contains significant power at low frequencies (7–10?years), while the northern pole (i.e., the one near Alaska) has no dominant frequencies. When examining the low-frequency content of the NPO and its poles separately, we discover that low-frequency variations (periods >7?years) of the NPO (particularly its subtropical node) are intimately tied to variability in central equatorial Pacific sea surface temperatures (SSTs) associated with the El Ni?o-Modoki/Central Pacific Warming (CPW) phenomenon. This result suggests that fluctuations in subtropical North Pacific SLP are important to monitor for Pacific low-frequency climate change. Using the simple AGCM, we also illustrate that variability in central tropical Pacific SSTs drives a significant fraction of variability of the southern node of the NPO. Taken together, the results highlight important links between secondary modes (i.e., CPW-NPO-NPGO) in Pacific decadal variability, akin to already established relationships between the primary modes of Pacific climate variability (i.e., canonical El Ni?o, the Aleutian Low, and the Pacific Decadal Oscillation).     

江南丘陵和云贵高原地形对一次西南涡暴雨影响的数值试验

运用MM5数值模式对1998年7月22~23日一次由西南涡引发形成湖南大暴雨的个例进行了数值试验。模式中设计了全地形、去掉江南丘陵地形、去掉江南丘陵和云贵高原地形三种方案。对比试验表明:在去掉江南丘陵和云贵高原后,由于地形的狭管作用消失,南北热力差异减弱,低空急流随之减弱;由于低空急流对西南涡和切变线的正涡度平流输送减弱,以及500 hPa高空槽引导切变线向南移与西南涡结合,造成西南涡增强,切变线减弱、消失。同时,本文还对三种模拟试验中地形作阶梯化处理,进一步验证江南丘陵、云贵高原对偏南风存在狭管作用,对低空急流的形成有促进作用。     

基于虚拟路由冗余协议和双向转发检测的基层气象通信网络设计和实现

目前陕西省气象宽带通信网省、市、县3级连接中,区县局出口是以单台路由器连接双运营商线路接入市局,这一架构造成明显的路由器单点故障风险,同时也不能有效解决台站各业务之间带宽竞争的问题。据此改造市-县级网络拓扑,在区县局出口部署双路由器,分别对接电信、广电运营商线路。启用VRRP(虚拟路由冗余协议),并配置VRRP的负载分担模式,对台站业务根据带宽消耗和时效性高低进行分流传输,在链路冗余的基础上实现了双机热备和负载均衡。同时配置BFD(双向转发检测协议)和VRRP联动,通过BFD监控VRRP路由器的上行链路状态,实现主备路由器的快速切换。经过在西安市多个区县局的广域网建设实践和一年多的业务运行,收到了预期的效果,方案可为同级气象部门提供参考。     

青海湖水位变化对青藏高原气候变化的响应

利用1959-2008年青海湖流域刚察和天峻站的降水、气温、风速及布哈河流量、青海湖水位高度、青藏高原地面加热场强度距平指数和青藏高原季风指数等逐月资料,分析了气候变化对青海湖水位年际波动的影响。结果表明,冬季青藏高原地面加热场的加强有利于青藏高原冬季风的加强,春末夏初(5～6月)青藏高原地面加热场强度的增强有利于青藏高原夏季风的提前(5～6月)加强;冬、春季青海湖流域风速与布哈河流量是引起青海湖水位年际差变化的主要因子;夏、秋季,青海湖水位年际差受流域降水量、风速和流量的共同作用,随着流域降水增加、入湖流量的加大、风速减小,水位年际差呈上升趋势(水位下降速度减慢)。建立了青藏高原热力作用和气候变化的关系及其对青海湖水位下降趋缓(年际差增大)的概念模型。     

气象资料同化的研究进展

回顾了国内外有关气象资料同化的研究进展，介绍了当前资料同化主要方法的理论基础、优缺点及应用研究。重点介绍了伴随方法和遗传算法在四维变分同化中的具体应用。其中，遗传算法的引入为资料同化的研究提出了新的思路。     

基于RS和GIS技术的矿山环境恢复与治理规划——以云南省元阳某金矿矿集区为例

矿产资源开发利用导致环境问题日益严重,为了给《矿产资源总体规划(2008—2015)》(简称二轮规划)方案的动态调整提供可视化的信息参考,为"矿山复绿"行动提供基础信息。该文以云南省元阳某金矿矿集区为试验区,利用GIS和遥感技术,提取该区矿业开发信息,结合自然地理和基础地质等资料,采用网格法对该区矿山地质环境进行评价,根据评价结果探索性地开展了矿山环境恢复与治理规划方案研究。结果表明,该方案比二轮规划方案更为合理可行。     

Mass Transfer Velocity and Momentum Vertical Exchange in Simulated Deep Street Canyons

A box model to simulate mass transfer inside deep street canyons and with atmospheric flow above is introduced and discussed. Two ideal deep street canyons with aspect ratios of 3 and 5 (the aspect ratio being the ratio between building height and street width H/W) are considered. This range of aspect ratios, found in many densely populated historical centres in Mediterranean cities as well as in other cities around the world, potentially creates high air pollutant concentration levels. Our model is based on a combination of analytical solutions and computation fluid dynamics (CFD) simulations using carbon monoxide (CO) as a tracer pollutant. The analytical part of the model is based on mass transfer velocity concepts while CFD simulations are used both for a preliminary validation of the physical hypothesis underlying the model (steady-state simulations) and to evaluate the concentration pattern with time (transient or wash-out simulations). Wash-out simulation curves were fitted by model curves, and mass transfer velocities were evaluated through a best-fitting procedure. Upon introducing into the model the contribution of traffic-produced turbulence, the modelled CO concentration levels became comparable with those obtained in real-world monitoring campaigns. The mass transfer rate between the canyon and the above atmosphere was then expressed in terms of an overall mass transfer velocity, which directly allows the evaluation of the mass transfer rate between the bottom volume of the canyon (pedestrian level) with the above atmosphere. Overall mass transfer velocities are reported as a function of the operating conditions studied (H/W = 3–5 and wind speeds = 2–8 ms⁻¹). Finally, a simple expression is reported for determining pollutant concentrations at the pedestrian level based on the overall mass transfer velocity defined.     

全球变暖减缓期陆地地表气温变化特征和CMIP5多模式的未来情景预估

2000年后全球气温的增温率显著下降,全球进入变暖减缓期.本文基于CRU(Climatic Research Unit) 观测资料,分析讨论了2000年后全球及欧亚中高纬度地区全球变暖的减缓特征,评估了CMIP5(Coupled Model Intercomparison Project Phase 5)试验多模式对全球变暖减缓的模拟及未来气温变化预估.结果表明,2000年后全球陆地平均地面气温的增温率大幅下降至0.14℃ (10 a)-1,仅为1976~1999年加速期增温率的一半.全球陆地13个区域中有9个地区的增温率小于2000年前,4个地区甚至出现了降温.其中以欧亚中高纬地区最为特殊.加速期(1976~1999年)增温率达到0.50℃ (10 a)-1,为全球陆地最大,2000年后陡降至-0.17℃ (10 a)-1,为全球最强降温区,为全球变暖的减缓贡献了49.13%.并且具有显著的季节依赖,减缓期冬季增温率下降了-2.68℃ (10 a)-1,而秋季升高了0.86℃ (10 a)-1,呈现反位相变化特征.CMIP5多模式计划中仅BCC-CSM1.1在RCP2.6情景下和MRI-ESM1模式在RCP8.5下的模拟较好地预估了全球及欧亚中高纬地区在2000年后增温率的下降以及欧亚中高纬秋、冬温度的反位相变化特征.BCC-CSM1.1在RCP2.6情景下预估欧亚中高纬地区2012年后温度距平保持在1.2℃左右,2020年后跃至2℃附近振荡.而MRI-ESM1在RCP8.5情景下预估的欧亚中高纬度温度在2030年前一直维持几乎为零的增温率,之后迅速升高.     

理想模拟的温带气旋中冷暖输送带特征分析

本文利用WRF理想斜压波模式模拟了理想湿大气中温带气旋的快速发展过程,采用拉格朗日轨迹筛选方法识别了气旋内部冷、暖输送带结构,分析了沿着输送带轨迹的物理量演变特征,探究了输送带气流对气旋降水结构的影响。本文在再现前人研究结论的基础上,发现了更精细的输送带结构特征,尤其是对冷输送带特征有了进一步认识。研究表明,根据相对气旋中心运动特征可将暖输送带划分为“前倾上升”和“后倾上升”两支。两支气流均起始于对流层低层冷锋前暖区内,旋转上升到对流层中高层出流区后分别向气旋中心的下游和上游运动,并在中高层产生负位涡扰动,促进高空系统发展。同时,暖输送带向上层输送水汽,影响锋面附近降水中心的形成和维持。在对冷输送带的研究中,本文证实了前人研究描述的上升类和低层运动类特征,而且发现其可以更精细地呈现出四支气流结构。“前倾上升”和“后倾上升”两支气流的初始位置靠近暖锋,上升运动到对流层中层后分别向气旋中心的下游和上游运动,利于促进暖锋附近降水形成;而“环气旋前倾”和“环气旋后倾”两支气流始终在对流层低层运动,初始远离暖锋朝向气旋中心运动,水汽含量增加,随后环绕气旋中心缓慢上升运动到气旋西侧后分别向气旋下游...