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1.
2006年超强台风“桑美”强度突变的动能特征分析 总被引：5，自引：0，他引：5
应用NCEP/NCAR再分析资料,对2006年超强台风“桑美”（Saomai）强度突变过程的动能特征进行分析,结果表明：“桑美”突然增强时刻其低层总动能和旋转风动能突然增加,辐散风动能也有所增加,总动能的增加主要是由旋转风动能增加所引起的;其高层总动能和旋转风动能突然减小,而辐散风动能突然增加,高层动能下传是导致“桑美”突然增强的重要原因;“桑美”突然增强时刻高层辐散风动能向旋转风动能的转换达到最大,低层辐散风与旋转风相互作用动能项达到最大;“桑美”突然减弱时刻的高低层能量变化趋势与突然增强时刻相反,并存在着低层动能的上传;“桑美”强度突变时对总动能（K）、旋转风动能（KR）、辐散风动能（KD）变化的响应时间为6～18 h。 相似文献
2.
在第(一)部分的基础上,进一步讨论辐散风动能和旋转风动能的收支以及这两种动能之间的转换过程。结果表明,尽管辐散风动能在总动能中所占比重很小,但它的变化与强对流天气过程的发生发展有着更为密切的关系。计算结果表明,在辐散风动能与旋转风动能的转换函数{KD,KR)中,B项(代表垂直运动与旋转风动能的垂直变化的耦合)是最大的转换项;在强对流区,反映涡管伸缩机制的A项也是一个很重要的转换项。就区域时间平均而言,有旋转风动能向辐散风动能(KR→KD)转换。 相似文献
3.
8014号热带气旋发生发展过程的能量学诊断研究 总被引：5，自引：1，他引：5
利用动能和总位能收支方程，对８０１４号强热带风暴过程进行了能量学诊断研究。结果表明，地转作用是该热带气旋中辐散风动能向旋转风动能转换的主要物理机制；非绝热加热是热带气旋发展的主要能源，其对总位能的制造大部分用于次网格耗散和侧边界输出，只有一小部分被转化为辐散风动能；两个转换函数Ｃ（Ｐ，Ｋｘ）和Ｃ（Ｋｘ，Ｋφ）在时空分布上具有很好的一致性；该热带气旋与周围环境场有明显的能量交换，在高层有总位能和旋转风动能输出，在低层有辐散风动能输入；在总动能收支中，辐散风作功是主要的功能产生项，旋转风作功主要是消耗动能。 相似文献
4.
梅雨锋次天气尺度涡旋旋转风和辐散风动能收支 总被引：2，自引：3，他引：2
本文选取１９９１年７月５日２０：００－６日２０：００梅雨锋上移动性次天气尺度涡旋引起的长江中下游特大暴雨为实例。采用准拉格朗日球坐标系的旋转风和辐散风动能方程，计算得到次天气尺度涡旋发展和成熟两个阶段对流层各层旋转风动能和辐散风动能的收支特征为：在对流层高层（１００－４００ｈＰａ）两个阶段的旋转风动能源汇相同，辐散风动能源汇有异，即水平动能通量项和“摩擦”项符号相反；在中层（４００－７００ｈＰａ） 相似文献
5.
本文计算和讨论4个不同类型暴雨过程各层次时空平均涡散场能量转换函数.指出其基本特征为:(1)对流层下层为最大正转换层,其转换强度和方向受C1+C2项制约,当暴雨发展时,能量转换急剧增长;而对流层上层的负转换强度则受控于C3项.但就对流层整层而言,能量转换函数C(K_χ,K_Ψ)均为正值,即势流动能向涡流动能转换,促使暴雨系统的维持和发展.(2)能量转换函数的水平分布,在对流层下层其正转换区与过程降水区较为一致,而在对流层上层的负转换区则位于过程降水区的北侧. 相似文献
6.
该文采用1998年加密观测资料经同化处理后得到的客观分析格点资料, 对南海地区和孟加拉湾地区的动能收支进行了诊断分析和对比, 得出: B区夏季风爆发, 其850 hPa区域平均总动能表现为爆发性增长, C区则表现为一个逐步增长的过程.越赤道气流通过南边界的动能输送对B区夏季风建立贡献很大, 西边界动能输入对C区夏季风建立也起了十分显著的作用.季风盛行期, B区夏季风动能的发展维持主要是动能水平通量散度的贡献, 其中西边界动能的流入贡献最大, 孟加拉湾夏季风的变化主要为印度季风影响所致; C区夏季风动能主要是依靠其区域内动能制造来维持.对于850 hPa层, B区主要通过斜压过程制造动能, 正压过程破坏更多的动能, C区主要是正压过程制造动能.两区对流层高层都为动能主要流出区, 而对流层低层, B区为动能流入区, C区为动能流出区. 相似文献
7.
本文通过对一次长江中游中尺度低涡的分析发现,在这类斜压性低涡发展时,低涡西侧冷区对流顶明显下降,在低涡区发生折叠现象.与大位涡值相联系的平流层空气从该处下沉至对流层,对流顶下陷比对流活动区对流顶高度变化要早且明显.中尺度涡旋发展所需要之动能主要取自辐散风动能,在对流层高层和低层这种正向转换最为清晰,而整个气柱中位能向辐散风动能转换,以支持它在涡旋发展过程中之消耗.但高层与低层的情况不同.在100hPa高空辐散风动能既支持了涡旋动能,又向总位能转换.分析表明,高层对流层流场在中尺度系统发展过程中是十分活跃的,必须引起足够的重视. 相似文献
8.
利用辐散风和旋转风的动能收支方程,对北方一次北上台风倒槽暴雨过程暴雨区内的涡散场能量收支和转换进行了计算.结果表明:暴雨区内动能的增加是暴雨增幅的一个主要原因.暴雨发展时,就旋转风动能(KR)而言,旋转风动能通量(HFR)辐合是主要能源,而旋转风的动能产生项(GR)是主要能汇;就辐散风动能(KD)而言,辐散风的动能产生项(GD)是主要能源,辐散风动能通量(HFD)辐散是主要能汇;总动能水平通量(HF)提供的辐合主要表现于对流层中、低层,这就使得低层辐合加强,上升运动加强,有利于暴雨的增幅.在暴雨过程中次网格尺度效应由能源转变为能汇,在暴雨发展之时能汇减小;能量的转换项C(KD,KR)总为正值,在转换项中,地转效应项的贡献很大.说明暴雨过程能量均由KD向KR转换,也就是说有效位能经KD向KR转换,充分说明了在整个暴雨过程中,尽管辐散风动能变化(∂KD/∂t)很小,但是它在其中充当“桥梁”作用,C(KD,KR)在暴雨发展时达到最大,此时能量转换最为旺盛;对流层低层辐散风动能向旋转风动能的转换是暴雨产生和发展的重要条件.此次暴雨过程,在暴雨区内表现为斜压不稳定和正压稳定共存的特征,其发展过程是系统斜压不稳定增长,正压稳定性减弱的过程,暴雨增幅的另一个重要原因就是暴雨区内低层斜压的发展. 相似文献
9.
利用高分辨率（10km）数值模拟的结果,以登陆华南并引发特大暴雨的0601号台风为例,对台风中田尺度动能收支平衡进行了诊断分析。结果表明,中-β尺度系统动能收支水平项（水平通量散度项和水平产生项）很小,垂直项（垂直通量散度项和垂直产生项）是动能收支方程的主要部分;动能垂直通量散度在对流层低层是动能的汇,在对流层中高层为动能的源;动能垂直产生项在对流层各层都是动能的汇;浮力产生项在300hPa以下是动能的源,在对流层高层是动能的汇;平均动能的局地变化项,在对流层各层均小于零,暴雨期间对流层动能支大于收,且动能变化在对流层中低层最明显。就整个对流层的垂直总量而言,浮力产生项是主要的动能源,而垂直产生项是主要的动能汇。较强冷空气首先从对流层中层入侵台风环流系统,抑制动能制造和传输,是中田尺度对流系统不能维持、发展的主要原因,也是台风系统及其暴雨不能长久维持的关键。 相似文献
10.
11.
计算大气中的长波辐射时,吸收气体的光学厚度要作气压订正,一般取气压订正后的光学厚度u′=(p/p_0)~K,对于O_3的9.6μ带,理论分析和实验都表明K是u和p的函数,气压订正可取 u′=(p/p_0)~(K(u,p))=uf(u,p). 我们以Walshaw的实验为基础,求出f(u,p)的囹形,并求出辐射通量及辐射通量散度的计算表。 当u很小时,弱线近似成立。漫射辐射的吸收率A_f=1-exp(-2su/d),K→0。在u→0时,dA_f/du=s2/d为一常量。 相似文献
12.
The local features of transient kinetic energy and available potential energy were investigated using ECMWF(European Centre for Medium-Range Weather Forecasts) Interim Reanalysis data for the stratospheric sudden warming(SSW) event of January 2009.The Western Europe high plays important roles in the propagation of the energy from North America to Eurasian.When the Western Europe high appeared and shifted eastward,energy conversions increased and energy propagated from North America to Eurasian as a form of interaction energy flow.The baroclinic conversion between transient-eddy kinetic energy(Ke) and transient-eddy available potential energy(Ae) and the horizontal advection of geopotential height were approximately one order of magnitude less than Ke and Ae generation terms.So,these terms were less important to this SSW event. 相似文献
13.
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
14.
2003年淮河流域大水期间体积降水量的研究 总被引：5，自引：2，他引：5
针对 2 0 0 3年梅雨期淮河流域大水提出了体积降水量的概念及其计算方法 ,在计算出淮河流域和其各子流域逐日和总体积降水量的基础上 ,将体积降水量与水文站的水位和流量进行了对比分析。结果表明 :水位对累计体积降水量有较好的即时响应 ,流量对体积降水量有较好的延迟响应。另外 ,讨论了流域体积降水量的预报问题 ,用国内外数值天气预报产品和中央气象台指导预报产品 ,进行了流域体积降水量预报试验 ,并对预报结果进行了检验分析。结果表明 :在目前天气预报水平条件下 ,利用数值天气预报和中央气象台业务预报产品制作体积降水量是可行的 ,能够延长洪水预报的预见期 ;而且 ,数值天气预报产品在预报体积降水量方面有明显的优势 ,因此可以直接利用数值天气预报产品进行体积降水量的客观预报 ,为防汛工作提供重要的依据。 相似文献
15.
利用多年逐月海温距平和区风应力距平观测资料,运用线性回归和ＥＯＦ分析方法,分析了ＥＮＳＯ相联系的热带太平洋典型风应力异常场结构。结果显示,与ＥＮＳＯ线性相关的风应力异常场在时间尺度上表现为低频变化,在水平结构上主要表现为四个典型分布。 相似文献
16.
Aerodynamic Parameters of Regular Arrays of Rectangular Blocks with Various Geometries 总被引：8，自引：8，他引：0
The aerodynamic effects of various configurations of an urban array were investigated in a wind-tunnel experiment. Three aerodynamic
parameters characterising arrays—the drag coefficient (C
d
), roughness length (z
o) and displacement height (d)—are used for analysis. C
d
is based on the direct measurement of the total surface shear using a floating element, and the other two parameters are
estimated by logarithmic fitting of the measured wind profile and predetermined total drag force. The configurations of 63
arrays used for measurement were designed to estimate the effects of layout, wind direction and the height variability of
the blocks on these parameters for various roughness packing densities. The results are summarised as follows: (1) The estimated
C
d
and z
o of the staggered arrays peak against the plan area index (λ
p
) and frontal area index (λ
f
), in contrast with values for the square arrays, which are less sensitive to λ
p
and λ
f
. In addition, the square arrays with a wind direction of 45° have a considerably larger C
d
, and the wind direction increases z
o/H by up to a factor of 2. (2) The effect of the non-uniformity of roughness height on z
o is more remarkable when λ
f
exceeds 20%, and the discrepancy in z
o is particularly remarkable and exceeds 200%. (3) The effect of the layout of tall blocks on C
d
is stronger than that of short blocks. These results indicate that the effects of both wind direction and the non-uniformity
of the heights of buildings on urban aerodynamic parameters vary greatly with λ
p
and λ
f
; hence, these effects should be taken into account by considering the roughness packing density. 相似文献
17.
This paper examines the practical importance of stability, baroclinicity, and acceleration in the bulk ABL similarity formulations, in light of the random errors inherent in field measurements. This is done by propagating the measurement uncertainties through a theoretical model for the bulk ABL similarity functionsA
0 andB
0, under a range of assumed (but always unstable) conditions. It is shown that random measurement errors and acceleration effects may overwhelm most effects of baroclinicity and stability, once conditions are at least slightly unstable. Because of this, it is hard to discern a clear functional dependence ofA
0 andB
0 on degree of instability. Thus, for a given value ofh
i/z0, whereh
i is the inversion height andz
0 is the surface roughness, the geostrophic drag coefficient, which depends onA
0 andB
0, and weakly onh
i/z0, may also be taken to be nearly independent of degree of instability. 相似文献
18.
Based on data obtained during the Hualhe River Basin Experiment （HUBEX） in 1999, this study intends to detect the quantitative discrepancies in the momentum （τ0）, sensible heat （H0） and latent heat （E0） fluxes among six sets of similarity functions with the aerodynamic method. It also aims to clarify the applicability of the functions under stable conditions. The relative discrepancy was studied with the normalized transfer coefficients for τ0, H0 and E0, namely CD, CH and CQ, respectively. Except for one set of functions that adopted a rather small von Kármán＇s constant （0.365）, the relative discrepancy in τ0 among the other functions was less than 10%, while that in H0（E0） sometimes reached 25% when the bulk Richardson number （R/B） was less than 0.07. The absolute discrepancy in the fluxes was studied with statistical computations. Among the six sets of functions, the discrepancy in τ0, H0 and E0 sometimes reached 0.03 kg m^-1 s^-2, 4 W m^-2 and 10 W m^-2, respectively, and the discrepancy in the energy balance ratio sometimes exceeded 0.1. Furthermore, when RiB exceeded the critical value （Ric） for a specific set of functions, no fluxes could be derived with the functions. It is therefore suggested that RiB be compared with Ric before computing the fluxes if RiB is less than Ric. Finally, two sets of nonlinear similarity functions are recommended, due to their unlimited applicability in terms of RiB. 相似文献
19.
On the basis of the budget equations for KR and KD, this paper presents the horizontal pattern of budget terms for two kinds of low level jets (LLJ) with and without heavy rain. The results show that the mechanisms for generating and maintaining LLJ are different, and especially, the direction of energy conversion is opposite. A positive conversion from KD to KR appears to be a necessary but not sufficient condition in the lower troposphere near the heavy rain area. The intensity and direction of energy conversion depends not only on the relative position of vorticity and divergence field, but also on the vertical profile of the jets directly. 相似文献
20.
Momentum Absorption in Rough-Wall Boundary Layers with Sparse Roughness Elements in Random and Clustered Distributions 总被引：1，自引：1，他引：1
A wind-tunnel experiment has been used to investigate momentum absorption by rough surfaces with sparse random and clustered distributions of roughness elements. An unusual (though longstanding) method was used to measure the boundary-layer depth δ and friction velocity u
* and thence to infer the functional relationship z
0/h = f(λ) between the normalised roughness length z
0/ h and the roughness density λ (where z
0 is the roughness length and h the mean height of the roughness elements). The method for finding u
* is based on fitting the velocity defect in the outer layer to a functional form for the dimensionless velocity-defect profile in a canonical zero-pressure-gradient boundary layer. For the conditions investigated here, involving boundary layers over sparse roughness with strong local heterogeneity, this velocity-defect-law method is found to be more robust than several alternative methods for finding u
* (uw covariance, momentum integral and slope of the logarithmic velocity profile).The experimental results show that, (1) there is general agreement in the relationship z
0/h = f(λ) between the present experiment with random arrays and other wind-tunnel experiments with regular arrays; (2) the main effect of clustering is to increase the scatter in the z
0/h = f(λ) relationship, through increased local horizontal heterogeneity; (3) this scatter obscures any trend in the z
0/h = f(λ) relationship in response to clustering; and (4) the agreement between the body of wind-tunnel data (taken as a whole) and field data is good, though with scatter for which it is likely that a major contribution stems from local horizontal heterogeneity in the field. 相似文献