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61.
The effect of mountainous topography on moisture exchange between the “surface” and the free atmosphere 总被引:1,自引:0,他引:1
Typical numerical weather and climate prediction models apply parameterizations to describe the subgrid-scale exchange of
moisture, heat and momentum between the surface and the free atmosphere. To a large degree, the underlying assumptions are
based on empirical knowledge obtained from measurements in the atmospheric boundary layer over flat and homogeneous topography.
It is, however, still unclear what happens if the topography is complex and steep. Not only is the applicability of classical
turbulence schemes questionable in principle over such terrain, but mountains additionally induce vertical fluxes on the meso-γ
scale. Examples are thermally or mechanically driven valley winds, which are neither resolved nor parameterized by climate
models but nevertheless contribute to vertical exchange. Attempts to quantify these processes and to evaluate their impact
on climate simulations have so far been scarce. Here, results from a case study in the Riviera Valley in southern Switzerland
are presented. In previous work, measurements from the MAP-Riviera field campaign have been used to evaluate and configure
a high-resolution large-eddy simulation code (ARPS). This model is here applied with a horizontal grid spacing of 350 m to
detect and quantify the relevant exchange processes between the valley atmosphere (i.e. the ground “surface” in a coarse model)
and the free atmosphere aloft. As an example, vertical export of moisture is evaluated for three fair-weather summer days.
The simulations show that moisture exchange with the free atmosphere is indeed no longer governed by turbulent motions alone.
Other mechanisms become important, such as mass export due to topographic narrowing or the interaction of thermally driven
cross-valley circulations. Under certain atmospheric conditions, these topographical-related mechanisms exceed the “classical”
turbulent contributions a coarse model would see by several times. The study shows that conventional subgrid-scale parameterizations
can indeed be far off from reality if applied over complex topography, and that large-eddy simulations could provide a helpful
tool for their improvement. 相似文献
62.
Terry van Dijk 《Geoforum》2007,38(3):505-511
An integral part of post-socialist transformation under the Washington Consensus has been the privatisation of previously state owned and/or co-operative farms. In many instances, there have been attempts at ‘turning back the clock’ to pre-War conditions, including land ownership structures. Frequently, the result has been the division of large, economically efficient units into numerous, small and economically barely viable private plots. Following accession to the European Union, these re-constituted peasant-scale structures pose a major challenge to the Union’s agricultural policy. As this paper demonstrates, a simple transfer of western European practices, such as land consolidation, is not possible. The particular legacies of the communist system have given land ownership particular values, legitimacy and personal identity, and emotional bonds. Simple technocratic solutions, as applied in the West earlier, are thus not feasible. Consequently, the paper points out, new forms and instruments of tackling disadvantageous agricultural structures need to be found. 相似文献
63.
64.
基层气象局地面测报工作是最基础的气象业务工作,为天气预报、气候分析、气象服务等提供重要的依据。根据多年在基层从事测报值班、报表预审及管理工作的经验,以及多次参加省、市测报业务竞赛的学习体会,分析了如何才能搞好这项工作,从而提高测报业务质量。 相似文献
65.
66.
利用辽东湾东海岸三个低空探测点的实测资料计算了各低空探测点的热内边界层平均高度,并将观测值与用经验公式得到的估算值进行了比较,给出了可用于这一地区的计算公式。 相似文献
67.
68.
Wen-yuan Huang Russ W. Keim Yao-chi Lu N. D. Uri Terry Kelley 《Environmental Geology》1998,34(2-3):116-127
The economic and environmental consequences of soil nitrogen tests can have significant impacts on agricultural production.
Some of these are explored here. The pre-side-dress soil N-test is evaluated for a hypothetical farmer growing corn at the
ARS Sustainable Agriculture Demonstration Farm site in southern Maryland. For a farmer not currently using a soil N-test,
adoption of this technology can lead to the enhancement of net farm income and the reduction in nitrogen loss to the environment.
This will transpire only if the farmer is currently underestimating nitrogen carryover by more than 25% or applying nitrogen
fertilizer based solely on an expected plateau-yield goal.
Received: 13 February 1997 · Accepted: 13 May 1997 相似文献
69.
曾胜兰 《成都信息工程学院学报》2015,30(1):96-101
城市热岛效应是城市气候最显著的特征之一。基于地理信息系统和不同时次的遥感影像,探讨成都市地表温度、热岛强度、热岛等级的分布特征及其演变。结果表明:成都市热岛效应明显且夜间夏强冬弱,地表温度呈条状分布;日间城市多数区域属于弱热岛以上等级,中心城区偏向强热岛和极强热岛,夜间强热岛面积扩张,冬季热岛等级增加明显;2002~2012年,城市热岛等级增加,强热岛面积扩张,但存在昼夜和季节性差异。 相似文献
70.
针对雨滴谱的变化对降水估计的影响,提出根据激光雨滴谱仪上方雷达回波的结构特征将降水过程划分为对流云降水和层状云降水交替分布5个部分,通过基于2种降水类型的第1种分类Z-R关系、基于5个部分的第Ⅱ种分类Z-R关系和基于整个降水过程的总体Z-R关系分析雨滴谱的变化对降水估计的影响.结果表明:当对流云降水向层状云降水过渡时,指数谱从无到有、多峰谱比例减小,Nw减小、μ增大、Dm变化不大;Mw与R变化相似,当Z增大时μ和Dm分别是递减和递增的;Z-R关系(Z=aRb)中a值变化范围较大、系数b在1~2波动且与层状云阶段相比,对流云阶段的a和b值较小;利用第Ⅱ种分类Z-R关系反演的雨强与基于雨滴谱仪观测数据计算的雨强最接近;雨滴谱仪在层状云阶段的反演效果明显强于对流云阶段,这与对流云降水中雨滴谱信息变化大且快等因素有关. 相似文献