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2015年12月在南京市郊进行雾的外场综合试验,观测得到20—21日雨后两次强浓雾的爆发性增强过程。利用常规气象资料、边界层廓线、雾滴谱等,分析此次典型雾过程的天气背景和边界层结构特征,探讨雾爆发性增强的原因。结果表明:雨后地表及近地层高湿环境为雾的形成提供了充足的水汽,南京冬季冷高压控制下稳定的天气层结,以及夜间的辐射冷却作用,极有利于辐射雾的产生。而雾的爆发性增强,主要和降温与增湿有关。晴天夜间地表向上长波辐射增强引起的强降温,日出后地面的强蒸发作用使得近地表水汽增多,都可直接引起雾的爆发性变浓。强的贴地逆温层的形成是雾爆发性增强的关键,易于近地面水汽的积累。而超低空急流的产生,有利于加速逆温层的贴地增强。 相似文献
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新疆北部强降雪天气研究若干进展 总被引:2,自引:0,他引:2
总结了近50 a来新疆北部强降雪的主要研究成果,从大尺度环流背景、天气尺度和中尺度系统、水汽特征及地形对强降雪增幅作用等进行了分类概述。提出了待解决的问题:造成新疆北部强降雪的各种尺度系统和短期环流异常、变化规律及其相互作用;不同区域强降雪及暖区和冷锋暴雪的区别及地形对各区域暴雪作用;不同区域强降雪的水汽源汇结构、远距离接力输送和集中机制及高、中、低纬度水汽输送和循环异常状况;中尺度系统的特征及其发生、发展的物理机制。这些问题的研究对推进新疆暴雪短期和短时预报的发展,提高预报准确率,增强防灾减灾能力具有重要意义。 相似文献
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采用欧洲中心1982年12月、1983年4月、1984年10月和1985年4月的月平均纬向风场实际观测资料,作为非线性临界层模式的基本气流进行数值积分,得到:用1982年12月和1983年4月的基流模拟出的副高强、范围大、数目少,维持2 ̄3个单体,且向西移,东西振荡周期1-2个月。用1984年10月和1985年4月的基流模拟出的副高弱、范围小,成带状分布,数目多达4个单体,副高合并、分裂得较快,亦 相似文献
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地形对于气流运动影响的数值研究 总被引:7,自引:3,他引:7
建立了二维、非静力平衡的数值模式,研究地形对上游气流的阻挡以及大振幅背风波谷与下坡风的形成。结果表明:地形的阻挡效应受地形高度、大气层结及地形非对称性等因子的影响。数值试验与理论分析都证明地形越高、层结越稳定时阻挡作用越强;同样条件下,迎风坡坡度大的地形容易对气流形成阻挡。此外,分析了地形高度、大气层结、地形非对称性以及基本入流大小对背风波谷及下坡风强度影响的规律,并通过一次实际观测对数值模拟结果进行了检验。 相似文献
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为更好地应用HDA算法产品并为进一步优化冰雹识别算法提供参考,应用2004—2010年武汉雷达和2007—2008年济南、青岛、烟台、宜昌、郑州和重庆共7部雷达监测到的28个直径大于等于19 mm的致灾性强冰雹天气个例,对CINRAD/SA雷达的强冰雹识别及最大冰雹直径(MEHS)预测产品进行了检验分析,同时对我国北方(济南、青岛、烟台、郑州)雷达和南方(武汉、宜昌、重庆)雷达的冰雹识别及大小预测效果进行了对比。结果表明:1)在不订正0℃层和-20℃层高度时,该算法对强冰雹天气的识别效果较好,但对MEHS的预测效果较差。2)每个雷达站对强冰雹识别和MEHS预测的效果差别不大,南方雷达和北方雷达对强冰雹的识别效果相近,但南方雷达对MEHS的预测效果较好。3)强冰雹识别和MEHS预测在5月份效果最好,8月份最差;该算法对大冰雹的识别效果较好,但仅对直径为40~49 mm的冰雹直径预测效果较好。4)冰雹识别产品对强冰雹的识别效果随所识别冰雹概率(POSH)增大而增强,当POSH=100时,临界成功指数CSI为100%,发生冰雹天气的可能性非常大。 相似文献
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利用2007-2013年新疆的十场强对流天气过程以及与之相应的FY-2D静止气象卫星数据,分析了强对流云红外一通道、红外二通道、水汽通道及通道差的光谱特征,提取强对流云团样本点,采用统计方法确定判识指标的阈值范围,构建多通道多阈值判识方法。利用三场天气过程的地面实测降水资料分别验证了单时次和整场天气过程强对流云判识的准确性,结果表明:单时次强对流云的识别区域与发生降雨台站一致的准确率为83%;在整个天气过程中,强对流频次分布与降水实况吻合度较高,说明随着对流云团的移动和发展,判识区域与地面降水区域保持一致,验证了判识方法有效,阈值选取合理,可以为监测暴雨天气系统的发生、发展提供支持。 相似文献
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利用常规气象资料、NCEP1°×1°再分析资料和北京多普勒雷达资料,对河北廊坊地区2020年2月14日强降雪过程中相态转变特征进行详细分析,并引入HYSPLIT模式,对强降雪地区气块进行96 h后向追踪模拟。研究发现:零速度线闭合状态反应了低空急流与中高空急流(气流)发展、对峙、消亡等状态,对地面降水相态变化的临近预报有较好指示意义;距离北京多普勒雷达40-80 km范围内的廊坊各地面气象观测站,在零度层亮带高度迅速下降后半个小时到1小时内先后完成雨雪相态转变;利用HYSPLIT模式得到强降雪地区四个高度层的水汽源地、路径及贡献,发现:700 hPa和850 hPa对降水区的水汽贡献较大,且均为暖湿气流。 相似文献
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利用WRF模式和GFS资料对乌鲁木齐机场一次东南大风天气进行了预报和地形敏感性试验。模式预报的结果表明:WRF模式对东南大风的起风时间、持续时间、风速大小等方面有较强的预报能力。地形敏感性试验表明:1乌鲁木齐市区与机场300m左右的高度差对机场风速的影响很大;2机场上空下沉运动的强弱与东南大风的强弱有很好的对应关系;3机场东南大风的风速变化并不总是与峡谷两端气压梯度力的变化同步。此次东南大风天气的产生是低空动量下传、狭管效应和下坡风共同作用的结果。动量下传主要出现在海拔2000m以下的高度,下坡风主要出现在海拔935m以下的高度。 相似文献
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Aerodynamic roughness of the sea surface at high winds 总被引:2,自引:0,他引:2
The role of the surface roughness in the formation of the aerodynamic friction of the water surface at high wind speeds is
investigated. The study is based on a wind-over-waves coupling theory. In this theory waves provide the surface friction velocity
through the form drag, while the energy input from the wind to waves depends on the friction velocity and the wind speed.
The wind-over-waves coupling model is extended to high wind speeds taking into account the effect of sheltering of the short
wind waves by the air-flow separation from breaking crests of longer waves. It is suggested that the momentum and energy flux
from the wind to short waves locally vanishes if they are trapped into the separation bubble of breaking longer waves. At
short fetches, typical for laboratory conditions, and strong winds the steep dominant wind waves break frequently and provide
the major part of the total form drag through the air-flow separation from breaking crests, and the effect of short waves
on the sea drag is suppressed. In this case the dependence of the drag coefficient on the wind speed is much weaker than would
be expected from the standard parameterization of the roughness parameter through the Charnock relation. At long fetches,
typical for the field, waves in the spectral peak break rarely and their contribution to the air-flow separation is weak.
In this case the surface form drag is determined predominantly by the air-flow separation from breaking of the equilibrium
range waves. As found at high wind speeds up to 60 m s−1 the modelled aerodynamic roughness is consistent with the Charnock relation, i.e. there is no saturation of the sea drag.
Unlike the aerodynamic roughness, the geometrical surface roughness (height of short waves) could be saturated or even suppressed
when the wind speed exceeds 30 m s−1. 相似文献
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This paper describes the leeside wind storm of 25–26 March 1998, the most intense wind storm of the last decade in Northwestern Greece. This wind storm produced wind gusts of 30 m s− 1 that resulted in tree uprooting, roof damaging, electric power network disruption and flooding in the lake-side areas of Ioannina city in Northwestern Greece. With the aim to identify the role of Mountain Mitsikeli near the city of Ioannina on the windstorm and to investigate the physical mechanisms responsible for such orographically induced weather events, numerical simulations with MM5 model have been performed. The model results showed that a resolution of 2-km resolution is necessary in order to reproduce the localized character of the wind storm. The analysis revealed that a synergistic combination of the cross-barrier northeasterly flow, the stable layer above the mountain top and the presence of a critical level, led to the intensification of the lee side winds during the studied wind event. Sensitivity experiments with modified topography, further supported the important role of mountain Mitsikeli that stands as an isolated obstacle, on the modification of the wind field during the observed windstorm. 相似文献
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基于频谱补偿和数值模拟技术的江苏近海大气边界层百米高度处极端风速研究 总被引:1,自引:0,他引:1
在平均风速基本满足近海风力发电需求的前提下,近海大气边界层百米高度处极端风速的合理估算成为中国海上风电开发领域的研究热点。与低纬度海域台风极端风速的广泛研究不同,由于缺乏有效的技术手段,对于台风影响相对较少的中纬度海域,极端风速的科学认识明显不足。研究以江苏近海为例,通过频谱分析技术,定量刻画了数值模拟风速能谱在高频波段的能量衰减和截断特征;进而利用风速能谱曲线在频率域的积分及其在高频波段的补偿,实现无观测区域年最大风速的估算。与台风风场数值模拟技术相结合,综合考虑了中国中纬度海域受寒潮大风和热带气旋大风影响的复杂、特有气候特征,建立了一套可推广应用的近海大气边界层百米高度处极端风速估算的新方法。据此推算了江苏近海100 m高度处50年一遇的极端风速。结果表明:受寒潮大风影响,江苏北部海域的50年一遇风速超过40 m/s;少量北上的热带气旋则造成响水和如东附近海域40 m/s,甚至44 m/s以上的50年一遇风速;中部盐城附近海域的50年一遇风速则普遍低于35 m/s。研究成果不仅为该海域近海海洋工程的开发设计及安全运行提供重要的科学支撑,同时也有助于加深对中国极端气候事件的科学认识和大气边界层科学理论的发展。 相似文献
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Severe downslope windstorms occurred on 5 April 2005 in the Taebaek Mountain Range, located in the eastern coast of Korea, are examined using the Weather Research and Forecasting (WRF) model. Strong winds are observed at Gangneung and Yangyang during two separate periods with a rapidly decreasing period in between. These downslope windstorms are reproduced in the simulation reasonably well, although the rapidly decreasing surface wind speed after the second windstorm could not be captured at Yangyang. It is found that the generation mechanisms of the downslope windstorms in these two periods are somewhat different. The severe wind in the first period is likely due to the reflection of the mountain waves from a critical level that locates near z = 8–9 km. Upward-propagating waves and reflected downward-propagating waves interact constructively in a duct between the critical level and the surface, resulting in strong surface wind. In the second period, the hydraulic-jump theory can be applied in that the wave breaking above the downstream induces a well-mixed region, and severe downslope wind is developed beneath this turbulent region as the streamlines descend along the downstream. Simultaneous lee wave structure is also reproduced during the second windstorm period. The sensitivity of the downslope wind speed to the change in the land-cover map showed that the absorption of trapped lee waves in the boundary layer reduces the downslope wind speed significantly after the second windstorm at Gangneung, improving the model performance, although with no significant impact at Yangyang. 相似文献
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利用常规天气资料、风廓线雷达探测资料、自动站资料、NCEP再分析资料及数值模拟资料,对乌鲁木齐2010年12月2-3日对飞行安全有较大影响的风切变颠簸天气进行了多角度分析。结果表明,局地性东南风层的形成和下传造成的水平方向上非东南风与东南风的切变、锋区南压过程中在北疆沿天山一带低空诱发的小范围风场扰动对东南风层短暂破坏而引起的水平和垂直方向上风向风速的迅即变化,是造成机场附近风切变颠簸的原因。中尺度数值预报模式(WRF)对此次风切变天气有较好的模拟能力,有助于在探测资料有限的情况下了解风切变的细微结构及其演变。 相似文献
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E. García-Ortega L. Fita R. Romero L. Lpez C. Ramis J.L. Snchez 《Atmospheric Research》2007,83(2-4):225-241
During the afternoon of August 16th 2003 a severe hail event occurred in the town of Alcañiz in the Ebro Valley (Spain). This storm brought with it intense rain and hail precipitation that caused severe floods, damaged cars and street furniture. A diagnosis, using data from ECMWF, showed the presence of a mesolow at surface level centered over the Northeast of Spain, carrying winds from the Mediterranean Sea towards the Central Ebro Valley. At medium and high levels, a trough, whose axis extended over the Northwest of the Iberian Peninsula, moved eastwards preceded at 500 hPa by a thermal trough that caused increasing instability before the arrival of the geopotential trough.A numerical study of this event has been carried out using the MM5 model with a double aim. On the one hand, it attempts to check whether or not the simulation reproduces the storm in Alcañiz. On the other hand, it carries out a sensitivity experiment in order to evaluate the contribution of two specific factors: topography and solar radiation. Compared with radar data, the control simulation reproduces the region affected by the storm reasonably well. The suppression of topography and/or solar radiation substantially modifies the surface mesolow and the spatial distribution of the precipitation. Neither of these factors, considered independently, reproduces the precipitation caused by the storm in Alcañiz. However, the results illustrate the importance of the synergic effect of these two factors on the spatial localization of the storm and on the intensity of the precipitation registered. 相似文献
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复杂山地近地层强风特性分析 总被引:10,自引:2,他引:8
利用在贵州省西南部复杂山地上获取的近地层梯度风观测资料和三维超声测风仪观测资料,从中筛选出具有该地气候特征的强风样本,利用数量统计和谱分析等方法,计算分析了由于复杂地形影响而导致的局地低层强风的平均和脉动特征.平均风场主要表现在受当地主要特征地形(西北-东南走向的深切峡谷)影响,其全年的主导风向和最大风速出现的方向几乎完全转为沿峡谷走向,即使在符合中性大气层结条件下,风的垂直廓线也完全不满足幂指数分布,风攻角远远大于规范推荐的值,并且不同风向的强风攻角因地形影响其差异可达20°;强风条件下脉动风场的主要特征是:不同风向强风的湍流强度有所不同,在纵、横和垂直方向的湍流强度比值与现行设计规范给出的三维湍流强度比值有明显差异,其中垂直方向的湍流强度显著偏大是突出特征;湍流积分尺度偏大,其中纵向值偏大20%-60%,横向值在某些风向上可偏大3倍以上,垂直方向则普遍较平坦地形偏大一个量级左右;在桥梁结构较为敏感的频域范围内,各风向的湍流谱密度值有显著差异,其中不同风向在纵向上最大差值可达8倍,横向和垂直向可相差6倍,但无论哪个方向的湍流谱密度值均比台风中心要小1-2个量级. 相似文献
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利用2017年6—8月的FNL再分析资料分析了新疆地区夏季平流层低层风场的时空演变特征,开展了平流层低层风场的高分辨率数值模拟和检验。结果表明:新疆地区夏季平流层纬向风随时间的变化存在经向差异,同时准零风层开始和结束的时间也存在经向差异,准零风层开始时间南部地区早于北部地区,而准零风层结束时间则相反。整个夏季新疆地区上空的准零风层处于70~40 hPa之间,其高度随时间呈先降低而后升高的变化趋势。准零风层数值模拟结果表明,模拟的准零风层参数与探空资料分析结果相比二者存在一致的变化趋势,准零风层起始高度的平均绝对误差为467 m,该高度对应的风速均方根误差为1.75 m/s。 相似文献