共查询到19条相似文献，搜索用时 95 毫秒
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依据水平风矢量场的分解思路,应用调和-余弦的二维风场分解方法,对水平风场的加速度迁移项也进行调和-余弦的分解,引入加速度迁移项位势概念,用加速度迁移项对应的位势分量部分对东移高原低涡及登陆台风系统的演变过程进行分析.结果表明:加速度迁移项位势对东移高原低涡系统有较好的描述作用.利用加速度迁移项位势追踪东移的高原低涡系统比常用的500 hPa位势高度场对低涡进行追踪更为清晰.此外,加速度迁移项位势在登陆台风Bilis的分析中也有较好的应用,可用以指示台风系统,判断台风中心的位置以及表示台风强度的变化.由于加速度迁移项位势可反映出水平风场平流的辐合辐散特征,因此对低涡及台风等与平流场的辐合辐散关系密切的天气系统的动力结构有较好的识别能力,可以作为一个新的动力诊断变量来诊断示踪天气系统的演变. 相似文献
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基于中尺度站点观测、雷达图像、卫星红外云图和NCEP全球业务分析数据资料,详细分析了2015年13号台风Soudelor在华东地区尤其在浙江省沿海产生局地灾害性强降水的分布、强度、触发因子及相应的动力过程.这次台风降水过程可分为4个阶段:第一阶段由台风北侧外围环流偏东风分量与浙江沿海地形相互作用而产生;第二阶段的降水强度最强,累积降水最大,是台风内区主体环流与局地地形相互作用的结果;第三阶段是由于台风内区减弱,主要降水云带在台风东北侧发展而形成;第四阶段由于台风环流与中纬度系统相互作用,使得降水云带"北跳"至江苏省中东部,引起浙江省内的降水迅速减弱.定量计算表明,"地形效应"对局地台风降水增幅起确定性作用,其在台风总体降水中占比达50%左右.台风登陆后结构变化引起水汽输送发生变化,进而引起台风局地降水云带发展的非对称分布,是造成台风强降水空间非对称分布的主要因子.对此个例分析表明,影响中国沿海灾害性强降水不仅与台风强度、结构及外围云带紧密相关,其降水强度会因为台风与沿海地形的复杂相互作用而增加,而其影响时间会因为由大尺度环流引导的弧线路径而延长.此次台风强降水过程的物理及动力分析可以用于指导对未来台风降水灾害的理解、预报及预防,尤其有益于由登陆台风与沿海地形相互作用引起的闪雨、山洪、泥石流及洪涝灾害的预报预警. 相似文献
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举力效应是指方向性切变气流经过地形激发的重力波能够使平均气流发生水平旋转.本文首先根据日本气象厅台风数据集统计了2006—2015年登陆台湾的台风个例,分析台风路径的偏转情况.然后利用二维傅里叶变换对欧洲中间尺度天气预报中心的再分析数据进行滤波,得到台风的环境大气层结和水平风场.最后根据台风环境风场以及台湾地形计算地形重力波举力,分析举力对台风路径偏转的可能贡献.结果表明,近十年共有20个台风登陆台湾,其中2006—2008年有10个.除去5个路径较为复杂的台风,本文对15个台风的地形重力波举力进行分析,发现有14个台风的路径偏转方向与举力方向一致.对于路径偏转最为明显的6个台风(偏转角度大于30°),地形重力波举力对台风路径偏转的贡献可达10%,部分解释了台风经过台湾地形时发生的路径偏转. 相似文献
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通过对波场矢量计算散度与旋度可将P波和S波进行分离,这种方法是波场传播与计算散度和旋度进行波场分离两部分的结合.基于二维各向同性介质速度模型,首先使用弹性波动方程对速度模型进行波场传播模拟;然后在地表接收多分量记录的同时计算散度代表P波、计算旋度代表S波,由于计算散度和旋度包括对空间各分量求导,这就导致了π/2的相位移,使用Fourier变换在频率域对记录进行-π/2的相位校正,就分别获得P波和S波的波场记录.通过对二维模型试算,并分析结果可知,采用计算散度和旋度进行波场分离是一种有效的方法. 相似文献
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《中国科学:地球科学》2021,(10)
2020年6月长江流域的降水量破了1979年以来的纪录.研究表明三个大洋(太平洋、印度洋和大西洋)都有贡献,但是大西洋起到主导作用.三大洋的海温异常可以影响两个区域的相对涡度异常:一个是位于华北地区的200-hPa相对涡度(华北涡度)负异常,另一个是位于南海的850-hPa相对涡度(南海涡度)负异常.长江流域的降水异常主要受到华北涡度相关的大气过程控制. 5月西北大西洋的海温正异常可以引起6月中纬度北大西洋的位势高度正异常,进而通过横跨欧亚大陆的大气波列影响华北涡度,从而造成长江流域的降水正异常.而印度洋和热带北大西洋,作为前一年冬季太平洋El Ni?o事件的电容器,可以引起南海涡度负异常(反气旋性环流异常),通过进一步加强水汽输送增强长江流域的降水.本研究表明5月西北大西洋海温是6月长江流域降水很好的预测因子,并且强调三大洋海温对中国极端天气和气候事件的重要作用. 相似文献
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本文分析长时间强度维持"菲特"台风不同发展阶段的位涡分布特征发现：台风内核区中尺度高值PV带及其变化与台风强度变化具有伴随关系，即高值PV区与内核区强对流不仅具有对应关系；而且其生命史与台风强盛维持期一致；此外在眼墙区附近位涡梯度最大.分析还指出：垂直剖面上的高值PV呈现由单极位涡态（台风发展加强期）向中空位涡态（台风强盛维持期）的转变，到台风快速衰减期，又形成PV量值较小的单极位涡态.位涡收支方程诊断表明：内核区域水平平流、垂直输送和凝结加热的初始增强和大值收支带不仅对台风内中尺度高值位涡分布及长时间强度维持具有重要影响，而且具有伴随关系.此外，位涡收支各项对位涡态的转变起着不同的作用，其中凝结加热在台风强盛期中空位涡塔的建立中作用明显，水平平流项则在眼墙区的位涡塔中上层有着正贡献，垂直输送在高值PV分布的再分配中起中介作用. 相似文献
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本文利用中国科学院空间科学与应用研究中心的瑞利激光雷达首次观测到了平流层地形重力波活动的现象,并结合美国国家环境预报中心(NCEP)的全球预报系统(GFS)的风场数据分析了该地形重力波的基本参数.与惯性重力波相比较,地形重力波的密度扰动没有下传的相位,在同一高度上,其扰动相位保持不变.北京空间科学与应用研究中心瑞利激光雷达自2012年开始观测实验以来,已经观测到多起地形重力波活动事件.本文以2013年11月11日的观测数据为例,研究北京上空的地形重力波活动,并结合GFS风场数据分析了北京上平流层地形重力波的波长、传播方向、传播速度等参量.通过分析得到在2013年11月11日北京上空存在一列传播方向为北偏西52.4°,水平波长为5.5km,平均垂直波长约为6.0km的地形重力波. 相似文献
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热带气旋是发生在热带洋面上的强烈气旋性涡旋.由于地转涡度梯度的存在,热带气旋在移动过程中不断发生Rossby波能量频散,并在热带气旋运动方向的后部激发出反气旋和气旋交替排列的Rossby波能量频散波列.多热带气旋共存和热带气旋的异常运动是当前国际热带气旋研究领域的热点问题,热带气旋Rossby能量频散被证实与多个热带气旋连续生成和异常运动密切相关.本文从热带气旋能量频散及波列特征、主要影响因子、反馈作用等方面,回顾总结了国内外关于热带气旋Rossby波能量频散的相关研究进展,并提出当前亟待解决的一些科学问题.目的是为深入研究热带气旋Rossby波能量频散及其影响提供基础和参考,以期使更多的研究学者关注热带气旋能量频散问题,从而进一步揭示热带气旋生成、发展和异常运动的动力学机理. 相似文献
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Landslides control the spatial and temporal variation of channel width in southern Taiwan: Implications for landscape evolution and cascading hazards in steep,tectonically active landscapes 
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下载免费PDF全文 Brian J. Yanites Nate A. Mitchell Joshua C. Bregy Grace A. Carlson Kirstyn Cataldo Margaret Holahan Graham H. Johnston Amelia Nelson Jeffery Valenza Matthew Wanker 《地球表面变化过程与地形》2018,43(9):1782-1797
Intense precipitation or seismic events can generate clustered mass movement processes across a landscape. These rare events have significant impacts on the landscape, however, the rarity of such events leads to uncertainty in how they impact the entire geomorphic system over a range of timescales. Taiwan is steep, tectonically active, and prone to landslide and debris flows, especially when exposed to heavy rainfall events. Typhoon Morakot made landfall in Taiwan in August of 2009, causing widespread landslides in southern Taiwan. The south to north trend in valley relief in southern Taiwan leads to spatial variability in landslide susceptibility providing an opportunity to infer the long‐term impact of such landslide events on channel morphology. We use pre‐ and post‐typhoon imagery to quantify the propagating impact of this event on channel width as the debris is routed through the landscape. The results show the importance of cascading hazards from landslides on landscape evolution based on patterns of channel width (both pre‐ and post‐typhoon) and hillslope gradients in 20 basins along strike in southern Taiwan. Prior to Typhoon Morakot, the river channels in the central part of the study area were about 3–10 times wider than the channels in the south. Following the typhoon, aggradation and widening was also a maximum in these central to northern basins where hillslope gradients and channel steepness is high, accentuating the pre‐typhoon pattern. The results further show that the narrowest channels are located where channel steepness is the lowest, an observation inconsistent with a detachment‐limited model for river evolution. We infer this pattern is indicative of a strong role of sediment supply, and associated landslide events, on long‐term channel evolution. These findings have implications across a range of spatial and temporal scales including understanding the cascade of hazards in steep landscapes and geomorphic interpretation of channel morphology. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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Recent observations of the tropical and subtropical atmosphere are interpreted in terms of scaling arguments and wave propagation theory advanced byCharney (1963, 1969).Charney’s idealizations describe the tropical atmosphere in terms of large regions of quasi-nondivergent flow containing small subdomains of heavy convection and divergence, and place emphasis upon the quasi-rotational regions. FGGE (First GARP Global Experiment) observations suggest that strongly divergent local tropical circulations are forced by latent heating and produce important direct modifications of the total wind field. We describe the extent to which the resulting field consists of divergent and rotational components in different analyses of the FGGE data, and present independent supporting documentation of the results in terms of heating estimates and rainfall observations. Local tropical heating rates on the order of 10°C/day are apparently due to latent heat release associated with precipitation rates as large as 6 cm/day during extended periods. The large contribution of the divergent wind is generally underestimated in models that do not retain such energetic local forcings, and this deficiency may be related to general underestimation of tropical-extratropical connections of many linear models. Such connections are commonly cited in relation to El Niño events, the Southern Hemisphere stationary-wave pattern, and in FGGE studies, but are not well simulated in most linear theories. It is not yet clear whether this is an inherent limitation of linear models, or whether the linear models have not yet explored all the potentially relevant ambient states. We explore the latter possibility by construction of a basic state that allows reasonable latitudinal evolution of the wave field. This basic state has zero absolute vorticity gradient throughout the tropics, and deviations linearized about this state are dynamically analogous to a “local” Hadley cell. To the extent that it is appropriate to regard the results in terms of wave propagation, our analysis suggests a prominent role for gravity-inertia waves in the tropics and for the extratropical connections. The relevance of gravity modes to observations and the theoretical explanation of the flat vorticity field remain to be established. 相似文献
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Typhoon Nuri formed on 18 August 2008 in the western North Pacific east of the Philippines and traversed northwestward over the Kuroshio in the Luzon Strait where it intensified to a category 3 typhoon. The storm weakened as it passed over South China Sea (SCS) and made landfall in Hong Kong as a category 1 typhoon on 22 August. Despite the storm’s modest strength, the change in typhoon Nuri’s intensity was unique in that it strongly depended on the upper ocean. This study examines the ocean response to typhoon Nuri using the Princeton Ocean Model. An ocean state accounting for the sea-surface temperature (SST) and mesoscale eddy field prior to Nuri was constructed by assimilating satellite SST and altimetry data 12 days before the storm. The simulation then continued without further data assimilation, so that the ocean response to the strong wind can be used to understand processes. It is found that the SST cooling was biased to the right of the storm’s track due to inertial currents that rotated in the same sense as the wind vector, as has previously been found in the literature. However, despite the comparable wind speeds while the storm was in western Pacific and SCS, the SST cooling was much more intense in SCS. The reason was because in SCS, the surface layer was thinner, the vorticity field of the Kuroshio was cyclonic, and moreover a combination of larger Coriolis frequency as the storm moved northward and the typhoon’s slower translational speed produced a stronger resonance between wind and current, resulting in strong shears and entrainment of cool subsurface waters in the upper ocean. 相似文献
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本文应用WRF(v 3.4)模式输出资料,揭示了风垂直切变(Vertical Wind Shear:VWS)在垂直方向上的波状变化特征,这种波状变化在台风不同发展时期又有不同形态,其中在持续强盛期呈双模态分布.应用VWS引起的次级垂直环流影响台风对流分布和强度变化的基本原理,用模式资料分析发现:对流层中层具有的VWS是整层VWS的主要部分,台风强度变化滞后VWS的形态突变6h左右;双模态波状变化的VWS产生的次级环流和台风垂直环流的配置不同使台风强对流带结构变得不对称及眼墙区对流强度在垂直分布上变得不均匀,随着持续强盛期涡旋运动的增强,强对流带分布又趋于对称.又根据VWS形成的垂直方向上涡度力分布不均匀引起台风内中尺度滚轴状对流带不稳定发展原理,分析表明:对流层中、低层的涡度力有利于对流不稳定增强,垂直速度的最大值与风垂直廓线的拐点在同一高度上,这与理论模型的结论一致.因此,VWS的波状变化分布特征不仅影响台风强对流带中尺度结构的改变,也对台风持续强盛具有重要作用;同时也是台风内滚轴状对流带不稳定的可能启动机制. 相似文献
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Typhoon-induced waves and surges are important when predicting potential hazards near coastal regions. In this paper, we applied a coupled modeling system for ocean–wave interaction to examine prediction capabilities for typhoon-induced waves and surges around the Korean Peninsula. To identify how ocean–wave coupling impacts wave and surge simulations during typhoon conditions, a set of comparative experiments was performed during Typhoon Bolaven (2012): (1) a fully coupled ocean–wave model, (2) a one-way coupled ocean–wave model without surface current feedback and ocean-to-wave water levels, and (3) a stand-alone ocean model without considering wave-based sea surface roughness (SSR). When coupled with the ocean model, the surface current reduced significantly the wave height on the right-hand side of the advancing typhoon track and improved prediction accuracy along the southern coast of Korea. Compared with the observed surge levels, the simulated surge height yielded improved results for peak height magnitude and timing compared with the uncoupled model. For wave-to-surge feedback, we found that wave-induced SSR plays an important role by modulating wind stress in the surface layer. The modulated wind stress directly affected the surge height, which improved surge peak prediction during the typhoon. 相似文献
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The thermospheric and ionospheric effects of the precipitating electron flux and field-aligned-current variations in the cusp have been modelled by the use of a new version of the global numerical model of the Earths upper atmosphere developed for studies of polar phenomena. The responses of the electron concentration, ion, electron and neutral temperature, thermospheric wind velocity and electric-field potential to the variations of the precipitating 0.23-keV electron flux intensity and field-aligned current density in the cusp have been calculated by solving the corresponding continuity, momentum and heat balance equations. Features of the atmospheric gravity wave generation and propagation from the cusp region after the electron precipitation and field-aligned current-density increases have been found for the cases of the motionless and moving cusp region. The magnitudes of the disturbances are noticeably larger in the case of the moving region of the precipitation. The thermospheric disturbances are generated mainly by the thermospheric heating due to the soft electron precipitation and propagate to lower latitudes as large-scale atmospheric gravity waves with the mean horizontal velocity of about 690 ms–1. They reveal appreciable magnitudes at significant distances from the cusp region. The meridional-wind-velocity disturbance at 65° geomagnetic latitude is of the same order (100 ms–1) as the background wind due to the solar heating, but is oppositely directed. The ionospheric disturbances have appreciable magnitudes at the geomagnetic latitudes 70°–85°. The electron-concentration and -temperature disturbances are caused mainly by the ionization and heating processes due to the precipitation, whereas the ion-temperature disturbances are influence strongly by Joule heating of the ion gas due to the electric-field disturbances in the cusp. The latter strongly influence the zonal- and meridional-wind disturbances as well via the effects of ion drag in the cusp region. The results obtained are of interest because of the location of the 相似文献
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Sunanda Nagar Sanjay Bawiskar Gurunath Chinthalu Jeevanprakash Kulkarni 《Pure and Applied Geophysics》2009,166(3):485-507
Monsoon depressions, the main rain-producing systems over the Indian region along and near their tracks, are found to intensify
the monsoon circulation by organizing low-level convergence. The normal track of the monsoon depressions is along the position
of the monsoon trough at the surface, i.e., northwestward from the Head Bay of Bengal. Most of the monsoon depressions dissipate
within one or two days after landfall. An unusual monsoon depression formed in the Bay of Bengal during the 1st week of August 2006 causing heavy to very heavy rainfall over Madhya Pradesh, Maharashtra and Gujarat States of India. The
track of this depression was anomalously southward from the mean track of the August depressions. It maintained its intensity
during its longer travel. This paper addresses some of the dynamical characteristics of the depression in relation to its
southward/westward track and longer travel. It is observed that horizontal advection of absolute vorticity above 550 hPa (below
600 hPa) along west (east) of the depression and maximum divergence of absolute vorticity below 400 hPa dominated for the
westward movement of the depression. Increased moisture supply from the Arabian Sea (after the landfall of the depression)
helped to maintain the intensity of the system throughout its long travel. The energy conversion terms revealed the strengthening
of the zonal flow at higher levels prior to the formation of the depression. 相似文献
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为了分析台风这类强对流诱发平流层重力波的过程,本文利用中尺度数值模式WRF-ARW(V3.5)和卫星高光谱红外大气探测器AIRS数据对2011年第9号强热带气旋"梅花"的重力波特征进行了分析.首先,针对模式输出的垂直速度场资料的分析表明,台风在对流层各个方向上几乎都具有诱发重力波的能量,而在平流层内则呈现出只集中于台风中心以东的半圆弧状波动,且重力波到达平流层后其影响的水平范围可达1000km.此外,平流层波动与对流层雨带在形态、位置以及尺度上均具有一定的相似性.其次,对风场的分析结果表明,不同高度上波动形态的差异主要是由于重力波垂直上传的过程中受到了平流层向西传的背景风场以及风切变的调制作用,揭示了重力波逆着背景流垂直上传的特征.随后,基于FFT波谱分析的结果表明,"梅花"诱发的平流层重力波水平波长中心值达到了1000km,周期在15~25h,垂直波长主要在8~12km.最后,利用AIRS观测资料分析了平流层30~40km高度上的大气波动,得到了与数值模拟结果相一致的半圆弧状波动.对比结果也验证了WRF对台风诱发平流层重力波的波动形态、传播方向、不同时刻扰动强度的变化以及影响范围的模拟效果.此外,也揭示了多资料的结合对比有助于更加全面地了解台风诱发平流层重力波的波动特征. 相似文献
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ZHOU Xuan YANG XiaoFeng LI ZiWei YU Yang BI HaiBo MA Sheng LI XiaoFeng 《中国科学:地球科学(英文版)》2013,56(11):1977-1987
The traditional method of Synthetic Aperture Radar(SAR)wind field retrieval is based on an empirical relation between the near surface winds and the normalized radar backscatter cross section to estimate wind speeds,where this relation is called the geophysical model function(GMF).However,the accuracy rapidly decreases due to the impact of rainfall on the measurement of SAR and the saturation of backscattered intensity under the condition of tropical cyclone.Because of no available instrument synchronously monitoring rain rate on the satellite platform of SAR,we have to derive the precipitation of the SAR observation time from non-simultaneous passive microwave observations of rain in combination with geostationary IR images,and then use the model of rain correction to remove the impact of rain on SAR wind field measurements.For the saturation of radar backscatter cross section in high wind speed conditions,we develop an approach to estimate tropical cyclone parameters and wind fields based on the improved Holland model and the SAR image features of tropical cyclone.To retrieve the low-to-moderate wind speed,the wind direction of tropical cyclone is estimated from the SAR image using wavelet analysis.And then the maximum wind speed and the central pressure of tropical cyclone are calculated by a least square minimization of the difference between the improved Holland model and the low-to-moderate wind speed retrieved from SAR.In addition,wind fields are estimated from the improved Holland model using the above-mentioned parameters of tropical cyclone as input.To evaluate the accuracy of our approach,the SAR images of typhoon Aere,typhoon Khanun,and hurricane Ophelia are used to estimate tropical cyclone parameters and wind fields,which are compared with the best track data and reanalyzed wind fields of the Joint Typhoon Warning Center(JTWC)and the Hurricane Research Division(HRD).The results indicate that the tropical cyclone center,maximum wind speed,and central pressure are generally consistent with the best track data,and wind fields agree well with reanalyzed data from HRD. 相似文献