Frequency response corrections for eddy correlation systems

Simplified expressions describing the frequency response of eddy correlation systems due to sensor response, path-length averaging, sensor separation and signal processing are presented. A routine procedure for estimating and correcting for the frequency response loss in flux and variance measurements is discussed and illustrated by application to the Institute of Hydrology's Hydra eddy correlation system.The results show that flux loss from such a system is typically 5 to 10% for sensible and latent heat flux, but can be much larger for momentum flux and variance measurements in certain conditions.A microcomputer program is included which, with little modification, can be used for estimating flux loss from other eddy correlation systems with different or additional sensors.     

Boundary-layer effects on cold fronts at a coastline

The present note discusses one physical mechanism which may contribute to cold air channelling, manifest as a frontal bulge on a surface-analysis chart, in the coastal region of Victoria in southeast Australia. This involves the modification of boundary-layer air in both offshore (prefrontal) and onshore (postfrontal) flow, and the effect on cross-frontal thermal contrast. The problem is discussed in terms of a north-south-oriented cold front behaving as an atmospheric gravity current, propagating along an east-west-oriented coastline, in the presence of a prefrontal offshore stream.     

Numerical simulation of the development of vortices over the Qinghai-Xizang (Tibet) Plateau

Summary Some of the vortices which develop over the Tibetan plateau during summer give rise to severe weather over eastern China. These weather developments can be difficult to forecast, but have been simulated successfully in a recently developed numerical model. It will be shown that different vortices respond differently to topographic effects, to nonlinear processes and to sensible and latent heating in their formation, maintenance, and motion. Elevated terrain appears to enhance the influence of thermodynamic processes, block airflow, and increase frictional dissipation.Sensible heating sometimes collaborates with topography in blocking cold air intrusions and is not only a function of terrain elevation but also of the synoptic situation. Without the input of latent heating, vortices over the eastern part of the Tibetan plateau tend to degenerate.

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Numerische Simulation von Wirbelbildungen über dem Hochland von Tibet

Zusammenfassung Einige der sich im Sommer über dem Hochland von Tibet entwickelnden Wirbel verursachen Unwetter in Ostchina. Die Vorhersage dieser Entwicklung kann schwierig sein, sie werden aber von einem kürzlich vorgestellten numerischen Modell erfolgreich simuliert. Es wird gezeigt, daß verschiedene Wirbel verschieden auf die Orographie, auf nichtlineare Vorgänge sowie auf fühlbare und latente Wärme in ihrer Entstehung, Erhaltung und Bewegung reagieren. Ein Hochland scheint den Einfluß thermodynamischer Vorgänge zu verstärken, Strömungen zu blockieren und die Reibungsdissipation zu steigern.Die fühlbare Wärme verhindert manchmal gemeinsam mit der Topographie Kaltlufteinbrüche, hängt aber nicht nur von der Hochland-sondern auch von der synoptischen Situation ab. Ohne latente Wärme neigen Wirbel über dem Ostteil des Hochlandes von Tibet zur Degeneration.

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With 22 Figures     

Interannual variation of Gulf Stream heat transport in a high-resolution model forced by reanalysis data

The variability present in a 1/6th degree Atlantic ocean simulation forced by analysed wind stress and heat flux over a 20-year period is investigated by means of heat transport diagnostics. A section is defined which follows the Gulf Stream and its seaward extension, and transport of heat across this section is analysed to reveal the physical mechanisms responsible for intergyre heat exchanges on a variety of time scales. Heat transport across another section that crosses the Gulf Stream is also diagnosed to reveal the temporal behaviour of the gyre circulation. The Ekman response to wind stress variations accounts for the annual cycle and much of the interannual variability in both measures. For the intergyre heat transports, cancellation by transient-mean flow terms leads to a very weak annual cycle. Transient eddies account for approximately half the total intergyre transport of 0.7 Petawatts. They also account for a significant fraction of the interannual variability, but separate experiments with repeated-annual-cycle forcing indicate that the transient eddy component of the heat transport variability is internally generated. Links between the intergyre transport, the wind-driven gyre circulation, the surface heat budget and the atmospheric North Atlantic Oscillation are discussed.     

江南南部—华南北部前汛期严重旱涝诊断分析

利用江南南部—华南北部区域18个站45年（1951～1995年）4～6月降水资料计算了Z指数,确定出该区域严重涝年（1954、1962、1968、1973、1975年）和严重旱年（1958、1963、1967、1985、1991年）。分析了严重旱涝的频数分布和空间分布的特征,以及印度洋和太平洋整个赤道地区的SSTA、OLR距平场的分布。结果表明旱涝年SSTA、OLR距平场均有明显的差异。     

Institutional Adaptation of Water Resource Infrastructures to Climate Change in Eastern Ontario

Institutional barriers and bridges to local climate change impacts adaptation affecting small rural municipalities and Conservation Authorities (CAs are watershed agencies) in Eastern Ontario (Canada) are examined, and elements of a community-based adaptation strategy related to water infrastructures are proposed as a case-study in community adaptation to climate change. No general water scarcity is expected for the region even under unusually dry weather scenarios. Localized quantity and quality problems are likely to occur especially in groundwater recharge areas. Some existing institutions can be relied on by municipalities to build an effective adaptation strategy based on a watershed/region perspective, on their credibility, and on their expertise. Windows of opportunity or framing issues are offered at the provincial level, the most relevant one in a federal state, by municipal emergency plan requirements and pending watershed source water protection legislation. Voluntary and soon to be mandated climate change mitigation programs at the federal level are other ones.     

克氏原鳌虾气象因子影响研究现状与展望

克氏原螯虾主要养殖在长江中下游地区,目前最主要的养殖模式为虾稻共作模式。大量研究结果表明,克氏原螯虾的生长发育与气象要素密切相关。水温在25-30℃时,克氏原螯虾生长较快;16-25℃水温范围内,温度越高,越有利于雌虾卵巢发育;20-30℃水温范围内,水温越高,受精卵孵化时间越短。光明和黑暗时间之比为16 h∶8 h时,最有利于雌虾性腺发育。与克氏原螯虾养殖有关的气象灾害主要有暴雨洪涝、高温热害、低温冷害。鉴于目前的养殖和气象因子影响研究及服务现状,建议气象部门开展虾-稻种养基地气象观测站网建设,开展气温与水温相关性和水温预报研究,以及气象要素对克氏原螯虾影响的定量化研究。     

Characteristics of Permeability Changes in Bituminous Coal Under Conditions of Stress Variation Due to Repeated Mining Activities

The factors affecting permeability change under repeated mining of coal seams are important study aspects that need to be explored. This study combined various stress variation characteristics of protective seam mining and simplified the stress path of repeated mining in protective seam mines. Based on the results from the bespoke gas flow and displacement testing apparatus, seepage tests for simulated repetitive mining were carried out. The results simulated the actual behavior very well. With any drastic increase in the mining influence, the axial deviation stress in the stress path increased, and the greater the difference in coal permeability during the unloading and stress recovery stage, the more substantial the increase in permeability. The change in coal permeability was significantly influenced by the severity of simulated repeated mining cycles. When the mining stress exceeded a critical value, the permeability of the coal sample increased with the increase in the number of loading and unloading cycles, but the reverse was true when the mining stress was lower than the critical value. The effective sensitivity of seepage to the applied stress decreased with an increase in the number of stress cycles. With a decrease in the deviation stress, that is, with lower severity of mining influence, the effective sensitivity of coal seepage to stress gradually decreased.