共查询到20条相似文献，搜索用时 31 毫秒
1.
A non-linear extension of the mixed spectral finite difference model for neutrally stratified surface-layer flow over complex terrain is developed. The non-linear terms are treated as additional source terms in the present model. The solution is calculated iteratively in spectral space, while the source terms are evaluated in physical space (at each iteration step) with the help of a Fast Fourier Transform algorithm.Results for simple 2D sinusoidal topography are shown to compare well with full non-linear finite difference results. The method, compared to conventional finite difference methods, has the advantage of rapid convergence and substantial savings in computer time. 相似文献
2.
A three-dimensional (3-D) inertial particle – Lagrangian stochastic model for heavy particles in turbulent flows has been
constructed. In this model, particle velocities are computed by adopting a non-linear drag law, while fluid velocity in the
vicinity of a particle is calculated using a 3-D Langevin equation. Our model results have shown that the inclusion of the
horizontal fluid velocity fluctuation computations and a non-linear drag law have an impact on the statistics of both fluid
and particles when compared with our earlier one-dimensional (1-D) model with a linear drag law. Model results are compared
and contrasted with Businger’s 1965 theory in terms of effective settling velocity. 相似文献
3.
A method is described for evaluating the ‘partial derivatives’ of globally averaged top-of-atmosphere (TOA) radiation changes
with respect to basic climate model physical parameters. This method is used to analyse feedbacks in the Australian Bureau
of Meteorology Research Centre general circulation model. The parameters considered are surface temperature, water vapour,
lapse rate and cloud cover. The climate forcing which produces the changes is a globally uniform sea surface temperature (SST)
perturbation. The first and second order differentials of model parameters with respect to the forcing (i.e. SST changes)
are estimated from quadratic least square fitting. Except for total cloud cover, variables are found to be strong functions
of global SST. Strongly non-linear variations of lapse rate and high cloud amount and height appear to relate to the non-linear
response in penetrative convection. Globally averaged TOA radiation differentials with respect to model parameters are also
evaluated. With the exception of total cloud contributions, a high correlation is generally found to exist, on the global
mean level, between TOA radiation and the respective parameter perturbations. The largest non-linear terms contributing to
radiative changes are those due to lapse rate and high cloud. The contributions of linear and non-linear terms to the overall
radiative response from a 4 K SST perturbation are assessed. Significant non-linear responses are found to be associated with
lapse rate, water vapour and cloud changes. Although the exact magnitude of these responses is likely to be a function of
the particular model as well as the imposed SST perturbation pattern, the present experiments flag these as processes which
cannot properly be understood from linear theory in the evaluation of climate change sensitivity.
Received: 16 January 1997/Accepted: 9 May 1997 相似文献
4.
A photochemical model of the atmosphere constitutes a non–linear, non–autonomous dynamical system, enforced by the Earth’s rotation. Some studies have shown that the region of the mesopause tends towards non–linear responses such as period-doubling cascades and chaos. In these studies, simple approximations for the diurnal variations of the photolysis rates are assumed. The goal of this article is to investigate what happens if the more realistic, calculated photolysis rates are introduced. It is found that, if the usual approximations—sinusoidal and step fiunctions—are assumed, the responses of the system are similar: it converges to a 2–day periodic solution. If the more realistic, calculated diurnal cycle is introduced, a new 4–day subharmonic appear. 相似文献
5.
T. N. Krishnamurti M. C. Sinha Vasubandhu Misra O. P. Sharma 《Dynamics of Atmospheres and Oceans》1998,27(1-4)
Over the upper troposphere of the polar latitudes the zonal flows exhibit a large variance on the time scale of the Madden-Julian oscillation, i.e. roughly 30–50 days. The other prominent regions for these intraseasonal oscillations are the Asian and Australian monsoon belts. These two regions are separated by the so-called critical latitude, to the south of which easterlies generally prevail and westerlies are prevalent to the north. A perplexing issue is that of possible tropical-middle latitude interactions across the critical latitude. The notion of the critical latitude emerged from the linear theories for the wave energy flux which assume a constancy in time for the zonal flows. This same problem, viewed in its full non-linear context, can be cast in a frequency domain. Such a formulation does not assume a constancy of the zonal flows in time but does permit the intraseasonal variations of the zonal flows to be present. The computation of the wave energy flux, from the more complete non-linear system in the frequency domain, requires the handling of linear, quadratic and triple product terms via use of Hayashi's co-spectral method. These results of the present study, based on 6 years of daily global data sets, show that wave energy flux clearly passes from the latitudes of the monsoon to the polar latitudes. A strong convergence of wave energy flux in the polar latitudes suggests the tropical-middle latitude convergence interactions across the so-called critical latitude—when the problem is viewed in the frequency domain. 相似文献
6.
B. Johns 《Dynamics of Atmospheres and Oceans》1976,1(1):91-98
A numerical model is used to study the effect of non-linearities on the dynamics of the boundary layer at the floor of a tidal channel. A feature of the model is the use of a non-linear transfer term to represent the effect of the turbulent stress in the system. Numerical evaluations are made in order to determine whether this term leads to distortions in the current profiles that are comparable with those normally associated with the inertia terms. Comparisons are also made between the predicted current profiles and those obtained from a simple Stokes' “shear-wave” solution. 相似文献
7.
中尺度扰动不稳定的数值研究 总被引：3，自引：0，他引：3
利用一个二维Boussinesq流体的绝热无粘非静力数值模式,将中尺度不稳定问题作为一个初值问题进行数值研究.线性情况下数值试验的结果基本与采用特征值方法研究得到的结论一致.非线性情况的数值试验表明,其不稳定发生的范围可与线性情况不一致;非线性不稳定的增长率一般较线性不稳定的增长率要小;非线性作用会造成波型的陡凸,从而造成流函数正负环流的不对称和环流流线的密集;非线性情形下的流型有些与强对流系统的流型相像. 相似文献
8.
《Dynamics of Atmospheres and Oceans》1999,30(1):1-24
A linear quasi-geostrophic model and a non-linear balanced model are used to study the properties of the oceanic baroclinic waves. From a linear point of view, the oceanic meso-scale (200–400 km) disturbances found near the Brazil and Falkland currents confluence zone seem to be generated by baroclinic instability. Non-geostrophic and non-linear effects due to a single original wave are superimposed on the linear fields associated with the most unstable wave. Characteristics very similar to observations are obtained in the evolution to finite amplitude. The evolution of oceanic thermal rings is very well reproduced by the non-linear model. However, the stage of saturation is not reached in the model results since the feedback to the thermal basic state is not included. 相似文献
9.
A quantitative scheme is put forward in our work of forecasting the storm rainfall of typhoons for specific sites.Using the initial parameters,weather situations and physical quantities as well as numerical weather prediction products,the scheme constructs multivariate,objective and similarity criteria for environmental factors for the time between the current and forthcoming moment within the domain of forecast.Through defining a non-linear similarity index,this work presents a comprehensive assessment of the similarity between historical samples of typhoons and those being forecast in terms of continuous dynamic states under the multivariate criteria in order to identify similar samples.The historical rainfall records of the similar samples are used to run weighted summarization of the similarity index to determine site-specific and quantitative forecasts of future typhoon rainfall.Samples resembling the typhoon being forecast are selected by defining a non-linear similarity index composed of multiple criteria.Trial tests have demonstrated that this scheme has positive prediction skill. 相似文献
10.
伴随技术是四维变分同化（4DVar）系统中计算代价函数梯度的最佳办法,切线性和伴随模式的效果和效率直接影响着4DVar系统的发展。基于GRAPES（Global and Regional Assimilation PrEdiction System）全球切线性和伴随模式1.0版本,利用GRAPES全球模式2.0版本在并行框架和性能等方面的改善,重新优化和设计了GRAPES全球切线性伴随模式2.0版本,提高了GRAPES全球切线性和伴随模式的效果和效率,优化了切线性模式程序结构,使其计算时间最优可控制在非线性模式的1.2倍以内;采用在切线性模式中保存基态的方法,重构了伴随模式的程序结构,使其计算时间最优控制在非线性模式的1.5倍以内;在GRAPES全球切线性物理过程的设计中,将线性物理过程的轨迹基态计算和切线性扰动计算解耦,提高了GRAPES全球切线性和伴随模式的计算效果和效率。 相似文献
11.
I. O. Yaroshchuk A. P. Leont’ev A. V. Kosheleva A. A. Pivovarov A. N. Samchenko D. V. Stepanov A. N. Shvyryov 《Russian Meteorology and Hydrology》2016,41(9):629-634
Spatiotemporal variability of the internal gravity waves in the Sea of Japan shelf zone (in the Peter the Great Bay) is analyzed basing on the results of the experimental data processing. It is shown that, as for autumn water structure, the tidal internal waves moving towards the coast are transformed due to the non-linear effects and may reach significant amplitudes (of about 10 meters). Such waves are usually referred to as strongly non-linear. The main characteristics of such intense waves were estimated. An example of the disintegration of solitary temperature depression into the package of short-period intense internal waves is given. 相似文献
12.
利用国家气候中心第2代季节气候预测模式BCC_CSM1.1(m) 的1991—2010年每年2月起报的历史回算资料集,考察模式对于5个夏季风指数的预测能力,并通过发展基于经验正交函数分解与相似分析的EOF-相似误差订正方法,对5个夏季风指数的模式预测进行再修正。交叉检验和独立样本检验结果表明:该模式对1991—2010年东亚夏季风指数与西北太平洋夏季风指数预测技巧较高;EOF-相似误差订正方法适用于模式预测技巧较低的指数,这些指数经订正后预测效果均有不同程度改进,而预测技巧较高的夏季风指数经订正后改进效果不明显;在交叉检验中,线性部分订正多优于非线性部分订正效果,而对于独立试报的年份,非线性部分订正多优于线性部分订正效果,显示出良好的应用前景。 相似文献
13.
A perturbation theory approach of non-linear mechanics is applied to the solution of a non-linear rotation anemometer dynamic equation in a gusty wind. The first two terms of the perturbation series give a simplified equation for the wind-speed overestimation by a rotation anemometer (u-error) in terms of a wind velocity spectrum (or a correlation function). The equation agrees satisfactorily with all the known analytical or numerical solutions of rotation anemometer equations. It agrees, in particular, with recent theoretical estimations of the u-error magnitude by Kondo et al. (1971) and Hyson (1972), but disagrees significantly with the experimental findings of Izumi and Barad (1970) and Högström (1974). The same approach is also used for the estimation of the influence of the vertical wind fluctuations on the rotation anemometer readings (w-error). It is shown that w-error is usually of the same sign as u-error and that the sum of these both types of errors may be in some cases of the same order as an experimental wind-speed overestimation observed by Izumi and Barad and by Högström. However, it seems probable that some additional types of errors contribute also to the real overspeeding of rotation anemometers in a gusty wind. 相似文献
14.
文章介绍了国家气象中心中期数值预报谱模式（T42L9）的非线性正规模初值化方案（NNMI）。讨论了该方案对资料同化和预报的影响。试验表明，应用前5个垂直模，经2次迭代能够得到一个对分析资料修正较小的平衡初始场。它成功地消除了预报中虚假的高频重力波振荡，对改进资料同化和模式预报起了重要作用。 相似文献
15.
A. K. Gu��ye Serge Janicot A. Niang S. Sawadogo Benjamin Sultan A. Diongue-Niang S. Thiria 《Climate Dynamics》2011,36(1-2):1-18
The aim of this work is to define over the period 1979?C2002 the main synoptic weather regimes relevant for understanding the daily variability of rainfall during the summer monsoon season over Senegal. ??Pure?? synoptic weather regimes are defined by removing the influence of seasonal and interannual time scales, in order to highlight the day by day variability of the atmospheric circulation. The Self-Organizing Maps (SOM) approach, a clustering methodology based on non-linear artificial neural network, is combined with a Hierarchical Ascendant Classification to compute these regimes. Nine weather regimes are identified using the mean sea level pressure and 850?hPa wind field as variables, and gathered into three classes. Two of these weather regimes represent the classical 3?C5-day African easterly waves with a mean wavelength of about 3,000?km. Three others are characterized by a modulation of the semi-permanent trough located along the western coast of West Africa and might be interpreted in terms of the 6?C9-day easterly waves. The last four weather regimes are characterized by a more or less strong north?Csouth dipole of circulation. They can be interpreted as a northward/southward displacement of the Saharan Heat Low for two of them, and a filling/deepening of this depression for the other two. The circulation patterns of all these nine weather regimes are very consistent with the associated anomaly patterns of precipitable water, mid-troposphere vertical velocity, outgoing longwave radiation, and finally rainfall. Rainfall distribution is also highlighted over the southwestern area of Senegal. 相似文献
16.
Summary A microwave radiometer with channels near the 18 GHz water vapor line and in nearby windows, the Special Sensor Microwave/Temperature-2 (SSM/T-2) was launched on a Defense Meteorological Satellite Program (DMSP) satellite in November of 1991. The instrument is intended to provide data for the retrieval of atmospheric water vapor profiles. Because the relationship between the radiances observed by the instrument and the water vapor profile are both non-linear and non-local and because of the influence of clouds, the interpretation of the radiances is inherently complex. Here we develop a simplified, albeit approximate, algorithm for the profile retrievals and test it with simulation studies. Specifically it is shown that for each channel of the instrument near the 183 GHz line there is a nearly constant overburden of water vapor above the height at which the atmospheric temperature equals the observed brightness temperature. This relationship, in turn, provides the basis for a simple analytic algorithm for the relative humidity immediately above that height.The simplified algorithm is useful as a first guess for iterative solutions to the non-linear equations and for a variety of analyses such as estimating the impact of uncertainty in the radiances or the temperature profile on the retrieved water vapor profile. It is also useful as a conceptual tool to aid in the understanding of the more complex algorithms.With 7 Figures 相似文献
17.
本文考虑高度非线性的大气中期运动是一种准涡旋运动,引用了准涡旋观点和方法来处理二维无辐散和三维运动方程,即在开始时保留涡旋项,而在对方程进行纬圈平均后,去掉一些涡旋项,得到了某些大气运动特征如西风指数、纬向动量和涡度的经向输送的纬圈平均值等的变化或摆动的振动方程,并求出谐波解。振动周期决定于经向动能二倍的纬圈平均值的平方根(v~2)~(1/2)。基本周期约二十天左右。 所得结果可能对极端复杂的大气运动总有出现中期振动的趋势和精致设计的圆盘模拟实验出现摆动的事实,提供某种程度的动力学解释,同时也可能对中期预报的实践提供一些依据。 本文的主要科学目的,是想指出对极端复杂的大气中期过程还是可能用线性理论来研究其某些特征的。 相似文献
18.
The concept of stability is discussed and results of the linear inviscid theory are reviewed. Examples are given to illustrate the point that stable stratification can, in some circumstances, be destabilizing due to the vorticity generated by non-homogeneity. The linear initial value problem is discussed and related to the more usual normal mode approach. Finally, the weakly non-linear theory and the non-linear critical layer theory are outlined. 相似文献
19.
线性化物理过程对GRAPES 4DVAR同化的影响 总被引：8，自引：3，他引：5
线性化物理过程能够改善四维变分同化中极小化收敛的稳定性和增加极小化过程中对大气物理过程和动力更加精确的描述,它是四维变分同化中非常重要的一部分。通过在GRAPES全球模式中研究线性化物理过程,尤其是两个湿线性化物理过程,改善切线性模式预报精度,来提高GRAPES全球四维变分同化的分析和预报效果。线性化物理过程的开发首先需要简化原非线性化物理过程中的强非线性项,然后对线性化物理过程进行规约化,以抑制切线性扰动的异常增长。目前GRAEPS全球模式中的线性化物理过程主要包括次网格尺度地形参数化、垂直扩散、积云深对流和大尺度凝结。线性化物理过程预报精度的检验方法是通过选择合适大小的初始扰动（同化分析增量）,来比较非线性模式和切线性模式中的扰动演化的纬向平均误差。然后以绝热版本的切线性模式为基础,通过冬、夏两个个例试验来分别检验4个线性化物理过程的12 h预报效果。试验结果表明,通过添加次网格地形参数化和垂直扩散两个干线性化物理过程方案,可以有效抑制住绝热版本切线性模式低层扰动的异常增长,大幅度改善切线性模式预报效果。通过添加积云深对流和大尺度凝结两个湿线性化物理过程,可以在热带区域和中、高纬度地区提高切线性模式中湿变量和温度变量的近似精度,提高GRAPES全球四维变分同化的分析和预报效果。 相似文献