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1.
2015年10月4日佛山龙卷过程的观测分析 总被引：4，自引：0，他引：4
受1522号台风彩虹外围螺旋云带影响,2015年10月4日15时28分—16时（北京时）广东佛山出现了EF3级强龙卷并造成严重灾害。为了综合分析龙卷发生的多尺度环境背景场和龙卷的结构及强度变化等特点,进行了灾情调研,航拍龙卷灾情路径,走访龙卷目击者,确认龙卷路径及灾情级别,再结合多渠道获取的龙卷视频照片等资料以及观测资料进行分析研究,结果表明:（1）产生此次龙卷的超级单体存在于台风彩虹外围螺旋云带内;龙卷向西北偏北方向移动,触地时长为32 min,受灾路径长度为31.7 km,最大受灾直径为577 m,平均速度约为60 km/h,具有“移动速度快,影响范围广,破坏力强”的特点,其移动速度快慢似与超级单体强度和地面的粗糙度有关。（2）佛山地区中高层受偏南气流控制,水汽充足,地面有弱冷空气;珠三角喇叭口地形有利于气流的辐合与局地涡旋的产生;抬升凝结高度低,风垂直切变大,有利于龙卷的生成。（3）地面自动气象站气象要素表现出受龙卷环流影响的特征。3 s极大风速的大值带和3 s最低气压的低值带以及1 h累计降水大值中心呈现出与龙卷走向一致的东南—西北向带状分布;龙卷到来时其周围自动气象站气温和气压明显降低,风速明显增大,风向明显改变;降水在龙卷靠近前5—10分钟就开始明显增大,其大值中心位于龙卷路径的西侧。龙卷离开后气压比龙卷来临前有所升高,但气温较前降低。（4）龙卷出现在钩状回波前进方向的右后侧;降水大值区与雷达组合反射率大值区基本一致。地面风场的辐合中心与龙卷触地的位置基本一致,并且钩状回波的入流区与地面偏东风区相对应。龙卷风暴单体发展高度在4 km左右,具有低重心对流的特点。其前部存在回波悬垂,一条很窄的向西北倾斜的回波大值带可能与龙卷漏斗云墙有关。对应径向速度剖面图上为一条向西北倾斜的正、负速度交界区,构成一个逆时针旋转的涡旋带,切向剖面图上存在较强的辐合。（5）龙卷发展过程中伴随着龙卷风暴顶和风暴底的逐渐下降以及单体质心的下降,中气旋与龙卷涡旋特征的顶和底也随之逐渐下降。龙卷风涡旋特征的顶高和底高都略低于中气旋,并在龙卷触地时降至最低。龙卷涡旋的切变值远大于中气旋的切变值,且在龙卷强度最强时最大。 相似文献
2.
基于多普勒天气雷达资料,结合中尺度数值模拟结果,对发生在黄淮流域的2次EF2级非超级单体龙卷风暴结构及低层流场结构特征进行了诊断分析。结果表明,2次龙卷过程都发生在副高边缘,低层存在较大的垂直风切变和强烈的水汽辐合;2次龙卷都有多次及地的特征,其母体风暴生命期都在2h以上;低层速度产品上有显著的小尺度涡旋特征,涡旋中心相邻像素之间的速度差＞20m?s-1,对EF2级龙卷预警具有6～20min的时间提前量;风暴后部中下层相对风暴的速度切变显著加强并迅速下传是诱发20100717龙卷涡旋的主因;风暴内部强烈上升气流导致低层涡旋发展,诱发20120818龙卷涡旋的产生。中尺度WRF模式模拟结果能够较好地再现风暴底部气流结构特征。 相似文献
3.
分析了2006年6月29日发生在安徽泗县的龙卷多普勒雷达的中气旋和龙卷涡旋特征（TVS）等产品。龙卷发生前,卫星云图上有3个对流云团呈东北—西南向排列,每个云团的东南侧有弓状回波发展,3条弓状回波首尾相连,也呈东北-西南向排列,龙卷发生在最西南的弓状回波的顶部。龙卷发生前弓状回波在上游产生了短时强降水,2 h降水量达到60 mm以上。在弓状回波的前沿,雷达探测到一系列的中气旋,龙卷发生前30 min,最西南的弓状回波追上其前面的回波带,发生了2个回波带合并,回波合并前,回波带上有2个中气旋,回波合并后,探测到一个特大直径的中气旋（径向直径25.8 km）。在龙卷发生地的上游,有一条带状的灾害性大风区,实地位置测定结果,该带状大风区与一系列中气旋最大风速圈的南边缘移过的路径一致。分析认为中气旋最大风速圈的南边缘,中气旋的风向与弓状回波后的直线风方向相同,两者叠加造成灾害性大风。出现龙卷1 h 40 min之前（05：00）,在泗县上游淮北地区,雷达开始探测到中气旋产品,在12 min之前探测到TVS（龙卷涡旋特征）产品,这些雷达产品对大风灾害的临近预报无疑是非常有用的。 相似文献
4.
5.
《干旱气象》2016,(4)
利用2013年甘肃华电阿克塞当金山49.5 m W风电场风机监控数据采集系统的观测数据,对BJ-RUC模式的低层风场预报产品进行质量检验。结果表明:(1)总体上有效风速区在各季节预测效果较满发风速区好,且这2个风速区秋季预报效果最好,冬季预报效果最差;(2)年尺度上,观测值的Weibull分布众值偏右,形态相对接近正态分布,而预测值的Weibull分布众值偏左,形态相对偏离正态分布。月尺度上,除1月外,其余各月实况和预测的Weibull分布与全年的基本一致,且各月预测风速形状参数k值接近2,为中性风,说明BJ-RUC模式模拟强阵性风速有局限性;(3)模拟的主导风向与实测的风向有较大偏差,仅对接近满发风速区的风向模拟得较准确,表明BJ-RUC模式对风向模拟有待提高。 相似文献
6.
通过降尺度模式CALMET不同参数化方案对江西山地风场测风塔风速风向模拟结果的对比分析,选取出适合山地风场模拟的最优参数化方案,并进行连续一年的模拟效果检验。结果表明:CALMET模式以不采用地形动力效应参数调整和Froude数调整,采用下坡气流效应调整和O’Brien垂直风速调整时,对江西省境内山地风场50 m以上高度层风场模拟效果最佳。最优参数化方案不仅能较好地模拟出山地风场测风塔逐时风速,并且对全年风速段分布模拟有较好的结果。CALMET模式能模拟出实际测风塔全年主导风向,但模拟与实测结果主导风向分布约有一个方位的偏差,主导风向频率有7%~8%的偏差。 相似文献
7.
8.
为了探讨云滴数浓度对于龙卷发生、发展的影响,利用ARPS（Advanced Regional Prediction System）模式,通过调整云滴数浓度（分别取高3000 cm-3、中1000 cm-3和低100 cm-3）的变化,对2003年7月8日安徽省无为县超级单体龙卷进行理想模拟试验。研究表明:三组试验都模拟出超级单体风暴的特征结构如钩状回波和V型入流缺口;云滴数浓度高的试验中上升气流更强、风暴较先发展且持续时间长,近地面涡度也较其他两组试验更大;从三组试验中找到4个龙卷涡旋,其中云滴数浓度高的试验中有两个,涡旋总持续时间接近30 min,最大近地面风速为46.93 m s-1,最大涡度值为0.42 s-1;高云滴数浓度情况下地面冷池弱,更有利于龙卷产生,并对龙卷的发生、发展有促进作用。 相似文献
9.
2013年3月20日广东东莞罕见龙卷冰雹特征及成因分析 总被引：1，自引：0，他引：1
利用常规观测、NCEP/NCAR再分析、多普勒天气雷达及自动气象站资料等,对2013年3月20日发生在东莞的一次罕见龙卷、冰雹等致灾性强对流天气过程进行分析。结果表明：1）龙卷过境时的单站气压、温度、风向风速与雷雨大风过境时明显不同,前者具有较典型的龙卷特征。2）华南地区高低空强的风随高度增大的垂直变化、上干下湿的位势不稳定层结以及低层高湿、增温为对流天气发展提供了有利的环境条件,冷空气南压和近地面边界层中小尺度辐合系统为其提供了触发机制。3）中等强度的对流有效位能（CAPE）、强的0-6 km深层垂直风切变以及较强的0-1 km低层垂直风切变为龙卷产生提供了可能性。4）龙卷、冰雹强对流风暴的发展加强与近地面边界层中小尺度辐合系统加强有密切关系。5）同时出现冰雹、大风、龙卷时,最强回波为72 dBz;龙卷出现在超级单体的钩状回波附近,更靠近后侧V形缺口;多时次观测到三体散射（TBSS）回波,与降雹对应;反射率垂直剖面图上可见明显的低层弱回波区、中高层回波悬垂,有界弱回波区（BWER）先于龙卷20多分钟出现。径向速度图上,龙卷出现时超级单体风暴同时具有龙卷涡旋特征（TVS）和中气旋特征。 相似文献
10.
随着计算能力的提升,台风数值模拟大量采用了大涡尺度模拟,其水平分辨率已达到数10 m的量级,而垂直分辨率提升不大,其问题是数值模式的垂直分辨率对台风大涡模拟的影响如何?因此,本文利用WRF(Weather Research and Forecasting)模式开展理想台风模拟,在不同的模式垂直层次(42,69和90层)情况下,研究并讨论数值模式垂直分辨率对台风大涡模拟的影响。结果表明,42层的垂直分辨率明显不足,而69层和90层的垂直分辨率则都能模拟出细致的台风边界层小尺度结构,龙卷尺度涡旋出现较多。与69层试验相比,90层试验模拟的台风强度要弱、龙卷尺度涡旋数量要少,但模拟的台风强度更稳定,模拟的小尺度涡旋也更精细。 相似文献
11.
Andrey A. Grachev Edgar L Andreas Christopher W. Fairall Peter S. Guest P. Ola G. Persson 《Boundary-Layer Meteorology》2007,124(3):315-333
Measurements of atmospheric turbulence made during the Surface Heat Budget of the Arctic Ocean Experiment (SHEBA) are used
to examine the profile stability functions of momentum, φ
m
, and sensible heat, φ
h
, in the stably stratified boundary layer over the Arctic pack ice. Turbulent fluxes and mean meteorological data that cover
different surface conditions and a wide range of stability conditions were continuously measured and reported hourly at five
levels on a 20-m main tower for 11 months. The comprehensive dataset collected during SHEBA allows studying φ
m
and φ
h
in detail and includes ample data for the very stable case. New parameterizations for φ
m
(ζ) and φ
h
(ζ) in stable conditions are proposed to describe the SHEBA data; these cover the entire range of the stability parameter
ζ = z/L from neutral to very stable conditions, where L is the Obukhov length and z is the measurement height. In the limit of very strong stability, φ
m
follows a ζ 1/3 dependence, whereas φ
h
initially increases with increasing ζ, reaches a maximum at ζ ≈ 10, and then tends to level off with increasing ζ. The effects
of self-correlation, which occur in plots of φ
m
and φ
h
versus ζ, are reduced by using an independent bin-averaging method instead of conventional averaging. 相似文献
12.
Data from the Antarctic winter at Halley Base have been used in order to evaluate qualitatively and quantitatively how the stratification in the low atmosphere (evaluated with the gradient Richardson number, Ri) influences the eddy transfers of heat and momentum. Vertical profiles of wind and temperature up to 32 m, and turbulent fluxes (
,
and
) measured from three ultrasonic thermo-anemometers installed at 5, 17 and 32 m are employed to calculate Ri, the friction velocity (u
*) and the eddy diffusivities for heat (K
h
) and momentum (K
m
). The results show a big dependence of stability onK
m
,K
h
andu
*, with a sharp decrease of these turbulent parameters with increasing stability. The ratio of eddy diffusivities (K
h
/K
m
) is also analyzed and presents a decreasing tendency as Ri increases, reaching values even less than 1, i.e., there were situations where the turbulent transfer of momentum was greater than that of heat. Possible mechanisms of turbulent mixing are discussed. 相似文献
13.
Summary Sublayer-Stanton numbers, Bi, of heat and matter for the interfacial sublayer over aerodynamically smooth surfaces determined for forced convective conditions
by elementary and numerical integration are reviewed and evaluated. The results are based on Roth’s modified Heisenberg model
for the spectral energy transfer in the equilibrium range under locally isotropic conditions and the approaches of Reichardt,
Elser, Deissler, van Driest, Rannie, Sheppard, and Spalding for the normalized eddy diffusivity Km/v. The results substantiate that with the exception of Sheppard’s Km/v-approach all formulations are appropriate to provide sublayer-Stanton numbers with a sufficient degree of accuracy. From
a theoretical point of view the Km/v-relationships of Roth, Reichardt, van Driest, and Spalding are to be preferred, when a turbulent Prandtl number Prt = 1 is presumed.
Since within the framework of mesoscale meteorological modelling numerical integration techniques would consume too much CPU-time
because of the large number of near-wall grid points, a parameterization formula for the sublayer-Stanton number is proposed
and evaluated. Compared to the Bi
−1-results obtained by numerical integration, this kind of parameterization leads to a relative error of less than 5 percent
for roughness Reynolds numbers, ηr, ranging from 30 to 600.
Received January 2001 Revised November 5, 2001 相似文献
14.
15.
Momentum and Heat Transfer over Urban-like Surfaces 总被引：2，自引：2，他引：0
Momentum and heat transfer was examined for the urban-like surfaces used within the Comprehensive Outdoor Scale MOdel (COSMO)
experiments. Simultaneous and comparative meteorological measurements were made over a pair of scale models with different
block geometries. These data were analyzed to investigate the influence of height variations, obstacle elongation, and packing
density, λ
p
, of blocks on the aerodynamic properties. In addition, the robustness of theoretical expressions of bulk transfer coefficients
for momentum and heat with respect to geometric parameters was examined. Our analyses showed: (1) the theoretical framework
for the bulk transfer coefficient for momentum, C
m
, and that for heat, C
h
, was applicable for homogeneous building arrays, (2) the sensitivity of C
h
to the surface geometry was smaller than that of C
m
, (3) the transfer coefficients were increased by variations of block heights, but not by elongation of blocks, (4) first-order
approximations of C
m
and C
h
for an array of blocks with two different heights can be made by applying simple theoretical assumptions to include the effects
of height variation, and (5) variations of block heights increased the momentum flux significantly, but caused little change
in the sensible heat flux. This can be explained by the feedback mechanism of aerodynamic– thermal interaction; aerodynamic
mixing decreased both the advective velocity and the vertical temperature gradient. 相似文献
16.
The Monin–Obukhov similarity theory (MOST) functions fε and fT, of the dissipation rate of turbulent kinetic energy (TKE). ε, and the structure parameter of temperature, CT2, were determined for the stable atmospheric surface layer using data gathered in the context of CASES-99. These data cover
a relatively wide stability range, i.e. ζ=z/L of up to 10, where z is the height and L the Obukhov length. The best fits were given by fε = 0.8 + 2.5ζ and fT= 4.7[ 1+1.6(ζ)2/3], which differ somewhat from previously published functions. ε was obtained from spectra of the longitudinal wind velocity
using a time series model (ARMA) method instead of the traditional Fourier transform. The neutral limit fε =0.8 implies that there is an imbalance between TKE production and dissipation in the simplified TKE budget equation. Similarly,
we found a production-dissipation imbalance for the temperature fluctuation budget equation. Correcting for the production-dissipation
imbalance, the ‘standard’ MOST functions for dimensionless wind speed and temperature gradients (φm and φm) were determined from fε and fT and compared with the φm and φh formulations of Businger and others. We found good agreement with the Beljaars and Holtslag [J. Appl. Meteorol. 30, 327–341 (1991)] relations. Lastly, the flux and gradient Richardson numbers are discussed also in terms of fε and fT. 相似文献
17.
Results from large-eddy simulations and field measurements have previously shown that the velocity field is influenced by
the boundary layer height, z
i
, during close to neutral, slightly unstable, atmospheric stratification. During such conditions the non-dimensional wind
profile, φ
m
, has been found to be a function of both z/L and z
i
/L. At constant z/L, φ
m
decreases with decreasing boundary layer height. Since φ
m
is directly related to the parameterizations of the air–sea surface fluxes, these results will have an influence when calculating
the surface fluxes in weather and climate models. The global impact of this was estimated using re-analysis data from 1979
to 2001 and bulk parameterizations. The results show that the sum of the global latent and sensible mean heat fluxes increase
by 0.77 W m−2 or about 1% and the mean surface stress increase by 1.4 mN m−2 or 1.8% when including the effects of the boundary layer height in the parameterizations. However, some regions show a larger
response. The greatest impact is found over the tropical oceans between 30°S and 30°N. In this region the boundary layer height
influences the non-dimensional wind profile during extended periods of time. In the mid Indian Ocean this results in an increase
of the mean annual heat fluxes by 2.0 W m−2 and an increase of the mean annual surface stress by 2.6 mN m−2. 相似文献
18.
The Bowen ratio (B) is impacted by 5 environmental elements: soil moisture availability, m, the ratio of resist-ances between atmosphere and soil pores, ra/rd, atmospheric relative humidity, h, atmospheric stability, ΔT, and environment temperature. These impacts have been investigated over diverse surfaces, including bare soil, free water surface, and vegetation covered land, using an analytical approach. It was concluded that: (a) B is not a continuous function. The singularity exists at the condition αhcb=h, occurring preferably in the following conditions: weak turbulence, stable stratified stability, dry soil, and humid air, where hcb, defined by Eq.(11) is a critical variable. The existence of a singularity makes the dependence of B on the five variables very complicated. The value of B approaches being inversely proportional to m under the conditions m≥mfc (the soil capacity) and / or ra/rd→0. The proportional coefficient changes with season and latitude with relatively high values in winter and over the poles; (b) B is nearly independent of ra/rd during the day. The impact of m on B is much larger as compared to that of ra/rd on B, (c) when h increases, the absolute value of B also increases; (d) over bare soil, when the absolute surface net radiation increases, the absolute value of B will increase. The impact of RN on B is larger at night than during the day, and (e) over plant canopy, the singularity and the dependcies of B on m, ra , and h are modified as compared to that over bare soil. Also (i) during the daytime unstable condition, m exerts an even stronger impact on B, at night, however, B changes are weak in response to the change in m; (ii) the value of B is much more sensitive in response to the changes of turbulent intensity; (iii) the B response to the variation of h over a vegetation covered area is weaker; and (iv) the singularity exists at the condition hcp=h instead of αhcb=h as over bare soil, where hcp is defined by Eq.(49). The formulas derived over bare soil also hold the same when applied to free water bodies as long as they are visualized as a special soil in which the volumetric fraction of soil pore is equal to one and are fully filled with water. Finally, the above discussions, are used to briefly study the impact on the thermally induced mesoscale circulations. 相似文献
19.
20.
Andrey Sogachev 《Boundary-Layer Meteorology》2009,130(3):423-435
The note presents a rational approach to modelling the source/sink due to vegetation or buoyancy effects that appear in the
turbulent kinetic energy, E, equation and a supplementary equation for a length-scale determining variable, φ, when two-equation closure is applied to canopy and atmospheric boundary-layer flows. The approach implements only standard
model coefficients C
φ1 and C
φ2 in the production and destruction terms of the φ equation, respectively. Numerical tests illustrate the practical applicability of the method, where, for example, simulations
with the E–ω model (where is the specific dissipation and is the dissipation rate of E) properly reproduce both the surface-layer wind profile estimated from the Monin-Obukhov similarity theory and the mixing-height
evolution observed above forested terrain in Southern Finland. 相似文献