共查询到20条相似文献，搜索用时 125 毫秒
1.
扰动特性对大气适应过程的影响和測风資料的使用問題 总被引：1，自引：1，他引：1
本文推导出斜压大气中适应过程的最終状态的一些公式,在极限情况下这些公式趋向于正压大气情况;并且这些公式非常明显地反映出最終状态对初始扰动的水平尺度及垂直結构的依赖关系。分析表明,在正压大气情况下,或者在斜压大气中,如果初始扰动随气压的分布此較均匀或者近于对数規律(相当于溫度場是上下均匀的),則当初始扰动的水平尺度L小于某个特征尺度L_0时是涡度場維持,气压場向涡度場适应;而当L>>L_0时,結果相反.在一般的斜压情况下情况很复杂.当初始扰动在大气低层有强烈垂直切变时,却是有利于气压場維持,风場向气压場适应。 将所得結論应用到分析某些大气动力过程.指出在一般情况下,使用实測风場作初始资料,按准地轉模式对流函数作数值預告,比用重力位势場作初始资料时要更合理些。 相似文献
2.
本文在考虑了热量对流輸送与层結间的相互作用基础上初步建立了对流热量輸送模式,并且作了数值計算.計算結果表明:热量輸送和大气层結之間的相互作用对热量輸送有着重要作用,在不稳定层結中热通量大大地超过稳定层結时的热通量。并且由于热量垂直輸送結果,大气层結开始时发生显著变化,最后趋向于中性层結. 相似文献
3.
个体积云发展演变特性的一些研究 总被引：1，自引：0，他引：1
本文先根据我国的观測事实,分析了个体积云发展演变的一些特性,并在理論上考虑了水滴对空气的拖带作用和水分相变(包括云外未飽和空气混合进云所引起的蒸发)的影响,假定个体积云为結构均匀的云块,由此計算了个体积云发展的层結条件和发展演变过程中的一些特性.計算結果指出,水滴拖带和水分相变作用对积云的发展条件很有影响;計算所得的个体积云发展演变特性与观測所得的結果也比較符合,可以对某些实际現象給以初步的理論解释. 相似文献
4.
5.
大气湍流的湍谱及有关大气污染问题 总被引：2，自引：0，他引：2
湍流运动是自然界和许多技术领域中出现的普遍现象。大气中所发生的许多现象都与湍流运动有关。但到目前为止,湍谱理论的发展还很不完善。特别是在大气或海洋中存在的大尺度湍流的湍谱理论就更不完善。 本文根据大量实测的湍谱数据(包括在风洞中、大气和宇宙空间中)反应出的湍谱分布规律,提出了一个描述湍流特性的无因次量R_i(R_i=D/v,D为湍流粘性系数, v为动力粘性系数),并用此无因次量对谱区作了划分。从高R_i数到低R_i数共分为三个谱区包括六个谱段。利用无因次量和相似性原理确定了适用于各谱区的能量传输函数的普遍形式,从而求解湍谱方程,得出了湍谱的普遍形式的解,其中包括了过去已有的两个主要结果。我们还求出了大气温度场和与大气污染有关的微粒浓度的湍谱。经与实测数据比较,发现两者符合得较好。 相似文献
6.
根据湍流应力模式的模拟结果，讨论了植被冠层中湍流能量的平衡特征，并通过数值试验就冠层结构对流场结构的影响进行了分析。 相似文献
7.
本文在分析戈壁地区湍流能谱特征的基础上,利用惯性副区有关规律,对湍流能量耗散率ε和温度脉动耗散率N作了初步研究,得到无因次湍流能量耗散率(?)_E为 无因次温度脉动耗散率(?)_N为 文中讨论了能量收支方程和温度方差收支方程,并用得到的(?)_E和(?)_N关系估算了近地面层的速度和温度特征尺度M和T,与涡旋相关方法得到结果比较,一致性较好。 相似文献
8.
本文运用相似理论,在物理分析的基础上试图从统一的观点来讨论不同温度层结下的湍流运动。由强迫对流到自由对流的过渡趋势假定是连续的,对极端稳定层结时湍流运动的特点提出了看法。选取了符合物理分析所要求的通用函数的形式,设法确定了其中的参数的值,并进而建立了根据梯度观测资料计算湍流系数及各种湍流输送通量的公式及图表,并用不同资料进行了检验。 相似文献
9.
暖云降水微观物理机制的統計理論 总被引：2，自引：0，他引：2
本文主要对暖云降水微观物理机制作了初步的实驗与理論分析,提出了云滴增长的随机过程理論以及暖云降水微观机制模式,結果表明,由于湍流所引起的起伏現象以及湍流碰并对降水的形成有极为重要的作用。 相似文献
10.
基于大涡模拟评估GRAPES模式对对流边界层的模拟性能 总被引：3，自引：1，他引：2
为检验GRAPES半拉格朗日动力框架在大涡尺度上的模拟性能,为未来发展千米及其以下高分辨尺度的数值模式奠定基础,并构造GRAPES大涡模式以检验和发展边界层湍流参数化提供科学工具。通过在GRAPES模式中加入Smagorinsky-Lilly小尺度湍涡参数化,并将模式分辨率提高至50 m,构建GRAPES大涡模式(GRAPES_LES),以便分析GRAPES模式在大涡尺度上的适用性。同时利用广泛应用的已有大涡模式UCLA_LES作为参考,通过对干对流边界层湍流的模拟分析及与UCLA_LES模拟结果的对比,得出如下主要结论:GRAPES半拉格朗日动力框架能够模拟出与已有的大涡模式相似的边界层湍流特征;同时,通过分析也证明GRAPES存在由于采用半拉格朗日平流计算而带来过度耗散的问题:当使用相同的滤波尺度(Smagorinsky 常数)时,GRAPES_LES模拟出的速度场更为平滑,小尺度湍流结构过于光滑,通过对湍流能量的能谱分析更清楚地表明了这一点。进一步,对不同的Smagorinsky常数(对应不同的滤波尺度)进行了敏感性试验,表明可以通过改变滤波尺度,有效地缓解半拉格朗日框架隐含的耗散问题,得到更接近UCLA_LES所模拟的湍流特征。 相似文献
11.
应用含湍流频散效应的近地面层的运动方程求解了不同层结下的风速廓线，着重分析了湍流频散效应对近地面层平稳运动的影响。分析指出：湍流的频散效应对经典的幂律廓线一对数修正，该修正在不稳定层结时比稳定层时明显；利用相似理论也得到了该常数。 相似文献
12.
13.
利用WRF模式结合不同的边界层参数化方案,对2007年7月3—5日发生在江淮流域的一次梅雨锋暴雨过程进行多组数值模拟试验。结果发现,边界层方案的选取对于降水的落区和强度模拟会产生较显著的影响;在降水率及地面要素的模拟上,各方案在降水中后期的模拟差异明显大于降水发生阶段;不同边界层方案的选取对于降水时段内的水平风场、垂直运动和假相当位温的垂直分布都产生影响,直接影响降水时空分布的模拟;不同方案都模拟出了在降水发生之后不同于晴空日变化的湍流动能垂直分布,经分析发现与局地较强的垂直风切变和近地面强湍流气团被抬升有关,而浮力项起着耗散作用;各方案的湍流交换特征与湍流动能特征基本吻合,相比于其他方案,MYJ方案在降水区域的湍流动能及湍流交换强度明显偏弱,对热通量的输送也偏弱;GBM方案在边界层内的湍流混合偏弱而在边界层以上湍流混合显著偏强,热通量输送在边界层以上的高度上误差明显,影响了对降水区域气象要素的模拟能力,仍需要进一步改进。 相似文献
14.
A wind-tunnel experiment was designed and carried out to study the effect of a surface roughness transition on subfilter-scale
(SFS) physics in a turbulent boundary layer. Specifically, subfilter-scale stresses are evaluated that require parameterizations
and are key to improving the accuracy of large-eddy simulations of the atmospheric boundary layer. The surface transition
considered in this study consists of a sharp change from a rough, wire-mesh covered surface to a smooth surface. The resulting
magnitude jump in aerodynamic roughnesses, M = ln(z
01/z
02), where z
01 and z
02 are the upwind and downwind aerodynamic surface roughnesses respectively, is similar to that of past experimental studies
in the atmospheric boundary layer. The two-dimensional velocity fields used in this study are measured using particle image
velocimetry and are acquired at several positions downwind of the roughness transition as well as over a homogeneous smooth
surface. Results show that the SFS stress, resolved strain rate and SFS transfer rate of resolved kinetic energy are dependent
on the position within the boundary layer relative to the surface roughness transition. A mismatch is found in the downwind
trend of the SFS stress and resolved strain rate with distance from the transition. This difference of behaviour may not be
captured by some eddy-viscosity type models that parameterize the SFS stress tensor as proportional to the resolved strain
rate tensor. These results can be used as a benchmark to test the ability of existing and new SFS models to capture the spatial
variability SFS physics associated with surface roughness heterogeneities. 相似文献
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16.
In an earlier paper by one of the authors (Smith, 1968), a momentum integral method was developed to parameterize the gross
constraint imposed by the surface boundary layer of a steady, axisymmetric, tropical cyclone on the meridional circulation
within the vortex itself. Specifically, the method provides an effective means of estimating the radial variation of mean
upflow/downflow induced by the boundary layer, compatible with a prescribed radial variation of azimuthal velocity just above
the boundary layer,V
gr. However, it relies on a judicious choice of vertical profiles of radial and azimuthal velocity components within the boundary
layer. An especially suitable set of profiles is discussed herein; these are Ekman-like profiles in which turbulent mixing
is characterized by a vertically constant eddy diffusivityK
M
, matched to a constant stress sublayer just above the sea surface. An attractive feature of the formulation is that a suitable
value forK
M
as a function of radius, which is extremely difficult to extract from observational data, can be calculated when the state
of the sea surface, described by a roughness lengthZ
0, is prescribed. Although observations ofZ
0 at high wind speeds are not yet available, the effect of radial variations in sea surface roughness can be assessed and it
is shown that these affect the upflow to a significant degree. 相似文献
17.
The radiative forcings and feedbacks that determine Earth’s climate sensitivity are typically defined at the top-of-atmosphere (TOA) or tropopause, yet climate sensitivity itself refers to a change in temperature at the surface. In this paper, we describe how TOA radiative perturbations translate into surface temperature changes. It is shown using first principles that radiation changes at the TOA can be equated with the change in energy stored by the oceans and land surface. This ocean and land heat uptake in turn involves an adjustment of the surface radiative and non-radiative energy fluxes, with the latter being comprised of the turbulent exchange of latent and sensible heat between the surface and atmosphere. We employ the radiative kernel technique to decompose TOA radiative feedbacks in the IPCC Fourth Assessment Report climate models into components associated with changes in radiative heating of the atmosphere and of the surface. (We consider the equilibrium response of atmosphere-mixed layer ocean models subjected to an instantaneous doubling of atmospheric CO2). It is shown that most feedbacks, i.e., the temperature, water vapor and cloud feedbacks, (as well as CO2 forcing) affect primarily the turbulent energy exchange at the surface rather than the radiative energy exchange. Specifically, the temperature feedback increases the surface turbulent (radiative) energy loss by 2.87 W m?2 K?1 (0.60 W m?2 K?1) in the multimodel mean; the water vapor feedback decreases the surface turbulent energy loss by 1.07 W m?2 K?1 and increases the surface radiative heating by 0.89 W m?2 K?1; and the cloud feedback decreases both the turbulent energy loss and the radiative heating at the surface by 0.43 and 0.24 W m?2 K?1, respectively. Since changes to the surface turbulent energy exchange are dominated in the global mean sense by changes in surface evaporation, these results serve to highlight the fundamental importance of the global water cycle to Earth’s climate sensitivity. 相似文献
18.
BOUNDARY LAYER STRUCTURE IN TYPHOON SAOMAI (2006): UNDERSTANDING THE EFFECTS OF EXCHANGE COEFFICIENT
Recent studies have shown that surface fluxes and exchange coefficients are particularly important to models attempting to simulate the evolution and maintenance of hurricanes or typhoons.By using an advanced research version of the Weather Research and Forecasting(ARW)modeling system,this work aims to study the impact of modified exchange coefficient on the intensity and structures of typhoon Saomai(2006)over the western North Pacific.Numerical experiments with the modified and unmodified exchange coefficients are used to investigate the intensity and structure of the storm,especially the structures of the boundary layer within the storm.Results show that,compared to the unmodified experiment,the simulated typhoon in the modified experiment has a bigger deepening rate after 30-h and is the same as the observation in the last 12-h.The roughness is leveled off when wind speed is greater than 30 m/s.The momentum exchange coefficient(CD)and enthalpy exchange coefficient(CK)are leveled off too,and CD is decreased more than CK when wind speed is greater than 30 m/s.More sensible heat flux and less latent heat flux are produced.In the lower level,the modified experiment has slightly stronger outflow,stronger vertical gradient of equivalent potential temperature and substantially higher maximum tangential winds than the unmodified experiment has.The modified experiment generates larger wind speed and water vapor tendencies and transports more air of high equivalent potential temperature to the eyewall in the boundary layer.It induces more and strong convection in the eyewall,thereby leading to a stronger storm. 相似文献
19.
本工作是在日本京都大学,防灾研究所的龙卷模拟实验室,用流体动力学模似实验方法研究三种不同粗糙表面对龙卷涡旋的影响。实验中,用热线风速表及微型风向标,测定了五个不同高度上的水平风速和风向分布,揭示出在不同粗糙表面上,龙卷涡旋的风速和风向分布特征。通过不断改变模拟装置的涡旋比S,发现当S值超过某一数值后(S>1.5),在不同粗糙表面上,龙卷涡旋的涡核尺寸将趋于一致。实验结果可进一步解释自然界中的观测事实,并对某些理论研究提供实验依据。 相似文献
20.
K.-P. Wittich 《Boundary-Layer Meteorology》1991,55(1-2):47-66
The stable boundary layer which evolved over the lowland of Northern Germany during a clear night with moderate geostrophic winds is studied. Because of the lack of turbulence measurements, a vertical flux-profile of heat and momentum is derived from a mean wind and temperature profile using an integral method. The stability parameter h/L
*
= 17 indicates that turbulence was sporadic during this particular night. This result is confirmed by the observed inertial oscillations, which occur not only in the residual layer but also in the boundary layer below.The case study shows that turbulent cooling overrules radiational cooling in the lower part of the surface inversion layer. Additionally, warm-air advection occurs. In the upper part, cold-air advection and radiational cooling dominate, while turbulent cooling is reduced. Subsidence warming can be neglected throughout the boundary layer during this particular night. 相似文献