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可照时数的含义是太阳中心自出地平线至入地平线,其直射光线在无地障及云雾烟尘遮掩情况下,照耀地面之时间。把一年或一月的实际日照时数与可照时数相比称日照比数或日照百分率。这对于研究云量分布和日照时间与农作物的生长关系,以及太阳能的利用都有一定的意义。 由天文学可知,某地的可照时数与该地的纬度及赤纬有关,其公式为: 相似文献
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海南州恰卜恰地区1993—1997年日照特征分析 总被引:2,自引:0,他引:2
利用海南州气象台1993~1997年地面观测资料,对恰卜恰地区的日照显时数、日照百分率、太阳能资源及云量、降水对日照时数的影响等进行了分析。结果表明:(1)日照时数具有明显的季节变化特征,春季高、冬季低;(2)日照百分率的分布情况则是冬季高、夏季低;(3)该地区的太阳能资料较为稳定,具有较强的开发和利用价值;(4)日照时数与云量、降水过程之间存在明显的负相关关系。 相似文献
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气象学报33卷第4期上兰鸿第等发表的“长江中下游水稻日照温度农业气候指标的初步研究”一文(以下简称原文),有其成功的一面。这里,不准备作全面评价,仅提出几个问题简单地讨论一下。 1.在日照长度与发育速度之关系的研究中,作者利用了可照时数。这样做,不够妥当。可照时数,很显然,仅属“可能”,并非“实际”。当然,并不是只有“晴天日照”才对植物 相似文献
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台站使用的暗筒式日照计,是利用通过仪器上的小孔射入筒内的太阳光在日照纸上留下的感光迹线计算日照时数的。上午和下午的日照迹线应是对称的两条曲线。可照时数是太阳中心从出现在一地的东方地平线到进入西方地平线,其直线光线在无地物、云、雾等任何遮蔽的条件下,照射到地面所经历的时间。因此,日照时数应<可照时数。然而,在审核或检查台站的记录时,却发现有日照时数>可照时数(或半天日照时数>半天可照时数)的现象。这往往是观测员在感光迹线的开始(或终止)处向前(或向后)多划铅笔线所造成。由于早上和傍晚太阳光线较弱,… 相似文献
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根据地球自转和绕太阳公转轨迹规律,分析了黄赤交角、太阳赤纬、经度和太阳高度角对日照迹线形成的影响,解释了春分、秋分、夏至、冬至几个具有代表性日期日照迹线形成的规律,阐述了暗筒式日照计日照迹线位置随季节变化的原理。地球运动轨迹固定,以地球作为参照物,地球相对静止,太阳围绕地球转,太阳光在无任何遮挡的情况下,每日的日照迹线可严格求出。用严谨的理论依据,导出日照迹线公式,并设计出软件,每日日照迹线可任意全真显示。 相似文献
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Walkability and livability in cities can be enhanced by creating comfortable environments in the streets. The profile of an urban street canyon has a substantial impact on outdoor thermal conditions at pedestrian level. This paper deals with the effect of asymmetrical street canyon profiles, common in the historical centre of Camagüey, Cuba, on outdoor thermal comfort. Temporal-spatial analyses are conducted using the Heliodon2 and the RayMan model, which enable the generation of accurate predictions about solar radiation and thermal conditions of urban spaces, respectively. On these models, urban settings are represented by asymmetrical street canyons with five different height-to-width ratios and four street axis orientations (N-S, NE-SW, E-W, SE-NW). Results are evaluated for daytime hours across the street canyon, by means of the physiologically equivalent temperature (PET index) which allows the evaluation of the bioclimatic conditions of outdoor environments. Our findings revealed that high profiles (façades) located on the east-facing side of N-S streets, on the southeast-facing side of NE-SW streets, on the south-facing side of E-W street, and on the southwest-facing side of SE-NW streets, are recommended to reduce the total number of hours under thermal stress. E-W street canyons are the most thermally stressed ones, with extreme PET values around 36 °C. Deviating from this orientation ameliorates the heat stress with reductions of up to 4 h in summer. For all analysed E-W orientations, only about one fifth of the street can be comfortable, especially for high aspect ratios (H/W > 3). Optimal subzones in the street are next to the north side of the E-W street, northwest side of the NE-SW street, and southwest side of the SE-NW street. Besides, when the highest profile is located on the east side of N-S streets, then the subzone next to the east-facing façade is recommendable for pedestrians. The proposed urban guidelines enable urban planners to create and renovate urban spaces which are more efficient in diminishing pedestrian thermal stress. 相似文献
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Juan Pedro Montávez Juan Ignacio Jiménez Antonio Sarsa 《Boundary-Layer Meteorology》2000,96(3):433-452
A model for the urban canyon is formulated for meteorologicalconditions of weak winds at night time. Thermal radiation, conductivity and convection are simulated by means of the Monte Carlo method. These are the main physical processesof energy transfer that give rise to the characteristic temperaturedistribution in these systems. The model has been satisfactory tested under ideal conditions for which analytical solutions exist.The predictions of the model under morerealistic conditions accurately reproduce the observationalresults. A strong temperature gradient across streets, with the canyon corners up to 4 °C warmer than the canyon centre, is found for the deepest canyons. This theoretical predictionhas been successfully verified with measurementstaken in a number of streets of the city of Granada in Spain. 相似文献
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Poor daytime and night-time micrometeorological conditions are issues that influence the quality of environmental conditions and can undermine a comfortable human lifestyle. The sky view factor (SVF) is one of the essential physical parameters used to assess the micrometeorological conditions and thermal comfort levels within city streets. The position of the visible sky relative to the path of the sun, in the cardinal and ordinal directions, has not been widely discerned as a parameter that could have an impact on the micrometeorological conditions of urban streets. To investigate this parameter, different urban streets that have a similar SVF value but diverse positions of visible sky were proposed in different street directions intersecting with the path of the sun, namely N–S, NE–SW and NW–SE. The effects of daytime and night-time micrometeorological variables and human thermal comfort variables on the street were investigated by applying ENVI-met V3.1 Beta software. The results show that the position of the visible sky has a greater influence on the street’s meteorological and human thermal comfort conditions than the SVF value. It has the ability to maximise or minimise the mean radiation temperature (Tmrt, °C) and the physiological equivalent temperature (PET, °C) at street level. However, the visible sky positioned to the zenith in a NE–SW or N–S street direction and to the SW of a NW–SE street direction achieves the best daytime micrometeorological and thermal comfort conditions. Alternatively, the visible sky positioned to the NE for a NW–SE street direction, to the NW and the zenith for a NE–SW street direction and to the zenith for a N–S street direction reduces the night-time air temperature (Ta, °C). Therefore, SVF and the position of the visible sky relative to the sun’s trajectory, in the cardinal and ordinal directions, must be considered during urban street planning to better understand the resultant micrometeorological and human thermal comfort conditions. 相似文献
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Summary. Building walls form an important component of the total surface area in cities, but are not generally considered in most
attempts to measure urban surface temperatures. A procedure which allows sampling of the spatial and temporal variation of
wall surface temperatures in urban areas is presented. Radiometric surface temperatures are monitored using an array of infrared
thermometers mounted on a moving vehicle. It is necessary to remove observations which view sky, or mixed sky and building
scenes. Distribution truncation and distribution modelling are investigated as methods to remove the unwanted observations.
Use of the traverse method in several urban areas reveals strong temporal variations in wall temperatures due to solar loading.
Significant spatial variations in temperatures suggest caution be used in the extrapolation of data from single canyon studies
to larger scales. Times of strong surface temperature contrast between different walls are linked to canyon and solar geometry.
In the light industrial and residential observation areas, north-south streets show mid-morning and late afternoon peaks of
approximately equal magnitude in the difference between wall surface temperatures. East-west streets show a single peak in
the hour following solar noon. The downtown study area, with streets oriented northeast-southwest and northwest-southeast,
shows a double wave pattern with one peak dominant. These patterns are of interest because they can lead to large biases in
remotely-observed surface temperature with view direction.
Received May 30, 1997 Revised July 20, 1997 相似文献
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A wind-tunnel experiment concerning atmospheric vortex streets 总被引:1,自引:0,他引:1
K. M. Barnett 《Boundary-Layer Meteorology》1972,2(4):427-443
Cloud patterns, in the upper part of the atmospheric boundary layer, with eddies similar to Karman vortex streets, have been observed in the lee of several isolated islands. An experiment was conducted to see if major features of these atmospheric vortex streets and associated atmospheric conditions could be simulated in a wind tunnel. A visible vortex street was observed in a wind tunnel while six atmospheric simulation criteria were at least qualitatively satisfied. The physical modeling, the atmospheric data used, the simplifying assumptions and approximations required, as well as the wind tunnel methods and results are described. 相似文献
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人口与GDP空间化技术支持下的暴雨洪涝灾害承灾体脆弱性分析 总被引:4,自引:3,他引:1
基于统计年鉴资料和土地利用数据,分别建立人口、GDP空间化模型,模拟南京市浦口区人口和GDP的空间分布。并结合暴雨洪涝历史灾情数据,探索区县级行政区域暴雨洪涝灾害承灾体脆弱性风险评估技术方法,最终获得100 m×100 m格网的浦口区暴雨洪涝灾害承灾体脆弱性空间分布图。研究结果表明:(1)人口、GDP的空间化模拟结果,既与各镇街统计数据保持一致,又反映了各镇街内部的人口、GDP分布的空间变化,可以为承灾体脆弱性评估提供精细化、可靠的数据源。(2)浦口区暴雨洪涝灾害承灾体脆弱性高风险区,分布在东北部经济较为发达的城镇街道而老山山脉和沿江内陆滩涂地区脆弱性风险较低。 相似文献
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An analytical model has been developed for the flow along a street canyon (of height H and width W), generated by an external wind blowing at any angle relative to the axis of the street. Initially, we consider the special
case of a wind blowing parallel to the street. The interior of the street is decomposed into three regions, and the flow within
each region is assumed to depend only on the external wind and the distance to the closest solid boundary. This decomposition
leads to two different flow regimes: one for narrow streets (H/W > 1/2) and one for wide streets (H/W < 1/2). The theoretical model agrees well with results obtained from numerical simulations using a Reynolds-Averaged Navier–Stokes
model. We then generalize the model to the case of arbitrary wind direction. Numerical solutions show that the streamlines
of the mean flow in the street have a spiral form, and for most angles of incidence, the mass flux along the street scales
on the component of the external wind resolved parallel to the street. We use this result to generalize the model derived
for wind blowing parallel to the street, and the results from this model agree well with the numerical simulations. The model
that has been developed can be evaluated rapidly using only very modest computing power, so it is suitable for use as an operational
tool. 相似文献