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1.
高强度降水过程形成和发展的一种机制分析 总被引：1，自引：4，他引：1
应用Sawyer-Eliassen次级方程诊断分析了一次高强度降水过程中的湿球位涡场，结合诊断结果探讨了高强度暴雨形成和发展的原因。分析表明：条件性对称不稳定是这次强降水发生的不稳定机制之一由强盛的西南低空急流输送的水汽在雨区低层辐合，地转动量近似下的锋生强迫形成的锋面次级环流促使暖湿空气向上输送，使聚集在其内的不稳定能量得以释放，导致强降水发生。 相似文献
2.
从Ｂａｅｒｉｓｗｙｌ－Ｂｉｓｈｏｐ模型出发，导出了严格的ＭＸ络合物链的连续哈密顿量，得到一组电子波函数满足的方程。进一步严格地求出这组方程的解析解。在零级近似下，该解回ＢＢ的简单扭折弧子解。文中采用的可推广到其他类似的系统。 相似文献
3.
采用滞弹性近似研究了WAVE-CISK下对称性扰动的谱点分布,得到了WAVE-CISK下对称不稳定扰动谱点分布的半圆定理,用其可估计该对称不稳定增长率的上界.发现存在WAVE-CISK时加热反馈和层结参数对该不稳定的增长率均有重要影响.WAVE-CISK加热反馈越强、基流的垂直切变越大,扰动的垂直结构越简单则该不稳定增长率的上界就越大.存在WAVE-CISK时滞弹性近似下的对称不稳定发生的条件也较Boussinesq近似下的更苛刻. 相似文献
4.
对于活塞压力计,零级有效面积是其最重要的参量。利用作为压力基准级活塞压力计活塞-活塞筒几何尺寸的测量结果,用几何法计算活塞压力计的零级有效面积和不确定度,活塞压力计零级有效面积计算结果为1961.0276 mm^2,其扩展不确定度为4.3 ppm（k=2,1 ppm=10^-6）;用压力平衡法获得活塞零级有效面积的结果为1961.0279 mm^2,其扩展不确定度计算结果为1 5 ppm（k=2）;用几何法获取活塞零级有效面积的不确定度最小,活塞零级有效面积为1961.0276 mm^2。 相似文献
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利用简单海气耦合模式，分析了经向风应力和纬向风应力对热带太平洋不稳定海气耦合模态的相对贡献。结果表明：在局地热力平衡假设下，海气相互作用导致了海洋Kelvin波的不稳定，该不稳定模态发生在一定波长范围内，只有纬向风应力对其作出贡献；在海温仅由平流过程决定的假设下，海气相互作用导致了海洋Rossby波的不稳定，该不稳定模态在整个波长范围内都有发生，波长越大，不稳定越强，经向风应力与纬向风应力都可以对海洋Rossby波的不稳定作出贡献，但是前者贡献较小；不稳定Rossby波比不稳定Kelvin波的增长率要小；由于无论哪一种不稳定模态，都是纬向风应力在海气耦合中起着绝对的主导作用，所以在研究热带太平洋海气耦合动力学对ENS0不稳定发展的贡献时，采用忽略经向风应力作用的近似是合理可行的。 相似文献
7.
圆形涡旋中的惯性重力内波不稳定和对称不稳定 总被引：10，自引：2，他引：10
用Boussinesq近似下的轴对称径向二维柱坐标系中的线性扰动方程组，讨论了圆形大气涡旋系统中扰动的惯性重力不稳定和对称不稳定。在环境为正压情形时，惯性重力内波不稳定的条件为#A(μj/R0)2N2+n2F2<0；当环境为斜压时，具有平行型扰动特征的惯性重力波发展的条件为Ri＊<1-[(3/2)+m]2，此时表现为对称不稳定。可见，惯性重力内波不稳定和对称不稳定都可作为台风、气旋一类圆形涡旋中扰动形成和发展的机制。 相似文献
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本文利用位于南京市郊区的南京大学仙林校区SORPES观测站多层湍流观测数据分析了湍流谱特征,以白天不稳定条件下垂直速度能谱谱峰对应的长度尺度也就是离地高度为判据,探讨了运用该方法确定复杂下垫面零平面位移的可行性。统计分析表明,该方法确定的长度尺度呈现出较为一致的概率分布形状,概率最大的长度尺度对应于离地高度,在复杂下垫面情况下这个高度就是零平面位移高度到观测高度之间的距离,将观测点的离地高度减去这个距离就能得到零平面位移。本文同时运用不稳定条件下垂直速度方差在近地层中的相似关系来确定零平面位移,并与谱方法得到的结果进行对比。结果表明,谱方法和方差法得到的零平面位移非常接近。 相似文献
10.
广义非线性亚临界湿对称不稳定 总被引：1，自引：1，他引：0
从含摩擦耗散与凝结潜热的f平面Boussinesq近似下的非线性扰动方程组出发,得到了湿空气中的广义能量方程,推导出非线性亚临界湿对称不稳定的必要条件,并将不稳定判据与干空气情况相比较,首先解析地分析得到凝结加热反馈机制对亚临界对称不稳定的影响。其次针对中尺度大气层结不稳定和稳定的情况,分别计算出初始扰动振幅的临界值,结果表明,相对干空气而言,饱和湿空气情况下,当中尺度大气层结不稳定时,亚临界对称不稳定更容易发生,即使中尺度大气层结稳定,亚临界对称不稳定也容易发生。这一结果改进了干空气下的非线性亚临界对称不稳定理论。 相似文献
11.
线性和非线性正压不稳定 总被引：4，自引：0，他引：4
本文从无摩擦的、无辐散的非线性正压涡度方程出发,利用行波解,在相平面上对方程的平衡点分别导得线性和非线性正压不稳定判据,与传统的不稳定判据作了比较分析。还求得了线性和非线性不稳定波的解析解,计算结果表明,若初始时刻两者波幅相等,则以后非线性不稳定波幅的增长值总小于线性不稳定波幅的增长值。非线性效应有使线性不稳定指数型增长减缓的作用。不稳定使得振幅比初始时刻增大一倍所需要的时间,对于线性不稳定大约是6h,对于非线性不稳定大约是18h,后者与实际大气中的观测事实是一致的。 相似文献
12.
NONLINEAR BAROCLINIC HAURWITZ WAVES 总被引：1，自引：1，他引：1
A family of nonlinear wave solutions, with Haurwitz waves as their zero-order approximations, to the baroclinic primitive equations is derived and the corresponding calculating system is presented. Numerical experiments with a two-level global model developed by ourselves confirm the validity of the theoretical results to a great extent. 相似文献
13.
A family of nonlinear wave solutions, with Haurwitz waves as their zero-order approximations, to the baroclinic primitive
equations is derived and the corresponding calculating system is presented. Numerical experiments with a two-level global
model developed by ourselves confirm the validity of the theoretical results to a great extent. 相似文献
14.
热带海气耦合Kelvin波的弱相互作用 总被引：3，自引：1，他引：2
本文在简单的热带海气耦合方程组中 ,引进基本风场和平均海流的作用以后 ,对热带海气耦合 Kelvin波的不稳定性进行了讨论 ,得到其耦合不稳定的判据条件 ,并且分析了它的传播结构特征。 相似文献
15.
Zhang Xuehong 《大气科学进展》1985,2(2):167-177
A kind of technique of computer extension of perturbation series is presented and used in seeking for the second-order approximation to a large-scale travelling wave solution of the barotropic primitive equations. Numerical experiments show that the second-order approximation keeps major characters of the travelling wave solution and is indeed more exact than the zero-order and the first order approximations. 相似文献
16.
A model is presented for the height of the mixed layer and the depth of the entrainment zone under near-neutral and unstable atmospheric conditions. It is based on the zero-order mixed-layer height model of Batchvarova and Gryning (1991) and the parameterization of the entrainment zone depth proposed by Gryning and Batchvarova (1994). However, most zero-order slab type models of mixed-layer height may be applied. The use of the model requires only information on those meteorological parameters that are needed in operational applications of ordinary zero-order slab type models of mixed-layer height: friction velocity, kinematic heat flux near the ground and potential temperature gradient in the free atmosphere above the entrainment zone. When information is available on the horizontal divergence of the large-scale flow field, the model also takes into account the effect of subsidence, although this is usually neglected in operational models of mixed-layer height owing to lack of data. Model performance is tested using data from the CIRCE experiment. 相似文献
17.
A recently discovered mechanism for producing step-like structure in a fluid's density field is explored under controlled laboratory conditions. Measurements of the conditions under which these “layers” exist, their direction, wavelength, and growth rate, are made and compared to the predictions of instability theory. The good agreement indicates that the layers are a result of a diffusive instability of a geostrophic shear flow. The instability can occur at higher and higher Richardson numbers, as the Schmidt number (ratio of diffusivities of momentum and salt) increases. Comparison of the density and velocity fields in the presence and absence of fully developed layers indicates that the instability functions mainly to transport momentum. Extrapolation of the measured wavelength to midlatitude oceanic conditions suggests that the momentum-density diffusive instability may play a role in producing meter-size oceanic microstructure. 相似文献
18.
Coherent Structures and the Dissimilarity of Turbulent Transport of Momentum and Scalars in the Unstable Atmospheric Surface Layer 总被引：7，自引：7，他引：0
Atmospheric stability effects on the dissimilarity between the turbulent transport of momentum and scalars (water vapour and
temperature) are investigated in the neutral and unstable atmospheric surface layers over a lake and a vineyard. A decorrelation
of the momentum and scalar fluxes is observed with increasing instability. Moreover, different measures of transport efficiency
(correlation coefficients, efficiencies based on quadrant analysis and bulk transfer coefficients) indicate that, under close
to neutral conditions, momentum and scalars are transported similarly whereas, as the instability of the atmosphere increases,
scalars are transported increasingly more efficiently than momentum. This dissimilarity between the turbulent transport of
momentum and scalars under unstable conditions concurs with, and is likely caused by, a change in the topology of turbulent
coherent structures. Previous laboratory and field studies report that under neutral conditions hairpin vortices and hairpin
packets are present and dominate the vertical fluxes, while under free-convection conditions thermal plumes are expected.
Our results (cross-stream vorticity variation, quadrant analysis and time series analysis) are in very good agreement with
this picture and confirm a change in the structure of the coherent turbulent motions under increasing instability, although
the exact structure of these motions and how they are modified by stability requires further investigation based on three-dimensional
flow data. 相似文献
19.
Xiao Qingnong 《Acta Meteorologica Sinica》1994,8(4):440-449
Following classical theory,a two-layer frontal model is designed.It assumes that frontal surface is the zero-order discontinuity of density.In this paper,the model is used to study orographically distorted and occluded fronts.It is indicated that the distortion and occlusion of cold fronts are different under different conditions of orography.Frontal intensity also influences the distortion and occlusion.Some rules are revealed and compared with observations.In addition,we have analysed the vertical structure of cold front above mountains and found that frontal surface may be bulged under the influence of orography when it climes the mountain.The bulge of frontal surface is just like the bore as pointed out by Long(1972) when he analysed fluid over obstacles. 相似文献
20.
Observations and Large-Eddy Simulations of Entrainment in the Sheared Sahelian Boundary Layer 总被引：1，自引：1，他引：0
Guylaine Canut Fleur Couvreux Marie Lothon David Pino Frédérique Saïd 《Boundary-Layer Meteorology》2012,142(1):79-101
At the top of the planetary boundary layer, the entrainment of air, which incorporates dry and warm air from the free troposphere
into the boundary layer, is a key process for exchanges with the free troposphere since it controls the growth of the boundary
layer. Here, we focus on the semi-arid boundary layer where the entrainment process is analyzed using aircraft observations
collected during the African Monsoon Multidisciplinary Analysis experiment and large-eddy simulations. The role of the entrainment
is specifically enhanced in this region where very large gradients at the planetary boundary-layer top can be found due to
the presence of the moist, cold monsoon flow on which the dry, warm Harmattan flow is superimposed. A first large-eddy simulation
is designed based on aircraft observations of 5 June 2006 during the transition period between dry conditions and the active
monsoon phase. The simulation reproduces the boundary-layer development and dynamics observed on this day. From this specific
case, sensitivity tests are carried out to cover a range of conditions observed during seven other flights made in the same
transition period in order to describe the entrainment processes in detail. The combination of large-eddy simulations and
observations allows us to test the parametrization of entrainment in a mixed-layer model with zero-order and first-order approximations
for the entrainment zone. The latter representation of the entrainment zone gives a better fit with the conditions encountered
in the Sahelian boundary layer during the transition period because large entrainment thicknesses are observed. The sensitivity
study also provides an opportunity to highlight the contribution of shear stress and scalar jumps at the top of the boundary
layer in the entrainment process, and to test a relevant parametrization published in the recent literature for a mixed-layer
model. 相似文献