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1.
四个耦合模式ENSO后报试验的“春季预报障碍” 总被引：2，自引：0，他引：2
用CliPAS计划中3个气候模式和中国科学院大气物理研究所耦合模式FGOALS-g短期气候异常回报试验结果,将动力和统计方法相结合,考察了1982—2003年厄尔尼诺/拉尼娜事件发展期和衰减期海表温度春季可预报性障碍现象。结果表明,所考察的耦合模式对ENSO事件预报的误差发展存在明显的季节依赖性,最大误差增长通常发生在春季,发生显著的可预报性障碍现象。进一步分析发现厄尔尼诺事件和拉尼娜事件在发展期的季节预报障碍现象比衰减期明显,以厄尔尼诺事件发展期春季可预报性障碍现象最为显著,拉尼娜事件衰减期季节预报障碍现象不显著。研究还发现,预报误差的增长在ENSO事件冷暖位相具有显著的非对称性,发展期暖位相预报误差强于冷位相,而衰减期冷位相的预报误差比暖位相大。通过回归分析,诊断了海-气相互作用的强度,发现耦合系统在春季最不稳定,使预报误差最易在春季发展,从而导致可预报性障碍。 相似文献
2.
进一步了球面上正压准地转运动中不稳定波的Ｈｏｗａｒｄ半圆定理，发现在某些特定的基本流分布下，该定理可以发展成圆弧定理，由此得到不稳定扰动增长率的更为精确的估计式。 相似文献
3.
把斜压气流中的短波槽看成波包，并把波包作为准地转模式的初值进行研究，发现波包的结构对其演变有重要影响，初始阶段急流轴下面向西倾斜的波包能够获得较快的发展，而向东倾斜的波包则是衰减的，这与ＷＫＢＪ方法得出的结论［１］是一致的，但是无论西倾还是东倾的波包，除了其自身随时间的演变外，还会激发出斜压不稳定波动，而且随着扰动的发展，不稳定斜压波会逐步在扰动中占主导地位。由此可以解释某些中纬度气旋的发生发展问题。 相似文献
4.
Y.L. McHall 《大气科学进展》1993,10(3):273-286
In development of baroclinic disturbances, baroclinity of basic temperature field varies with conversion of available potential energy. The growth rate which depends on the baroclinity varies as well. However, in previous linear theories, the growth rate was considered constant, so development of disturbances was not constrained by energy sources in the linear theories. In terms of energy conservation and conversion in an isolated atmosphere, we may study the variations in the baroclinity and growth rate and draw the corresponding pictures of perturbation developments in the varying environments. The amplification for the most unstable Eady wave is discussed as an example. It will be found that growth of baroclinic perturbations constrained by energy conservation is significantly different from the growth at the initial constant rate after mature stage. 相似文献
5.
The linear and weakly nonlinear dynamics of long, low frequency, spatially growing baroclinic waves embedded in slowly varying zonal flow on a β-plane channel are examined in a continuous model of the atmosphere. For a basic state jet flow possessing a locally unstable region, the nonlinear solution yields a maximum amplitude that is located near the region of maximum baroclinicity and substantially upstream of the maximum amplitude obtained from linear theory. The difference between the linear and nonlinear solutions is due to the time-averaged wave fluxes becoming large enough in the nonlinear problem to stabilize the flow prior to reaching the location (jet center) where the basic state baroclinicity and locally computed linear growth rate are maximized. 相似文献
6.
在满足有界条件的数值解是计算稳定的定义下, 讨论了辐射加热问题的时间积分, 并证明:如辐射加热和其对时间的一阶微商均连续时, 用向前差分格式计算的数值解是计算稳定的。还用一个例子证明:问题的数值解可以收敛到其解析解。 相似文献
7.
Since the solution of elliptic partial differential equations continuously depends on the boundary condition, the Euler equation derived from variational method cannot be solved without boundary condition. It is often difficult to provide the exact boundary condition in the practical use of variational method. However, in some application problems such as the remote sensing data assimilation, the values can be easily obtained in the inner region of the domain. In this paper, the boundary condition is tried to be retrieved by using part solutions in the inner area. Firstly, the variational problem of remote sensing data assimilation within a circular area is established. The Klein-Gordon elliptic equation is derived from the Euler method of variational problems with assumed boundary condition. Secondly, a computer-friendly Green function is constructed for the Dirichlet problem of two-dimensional Klein-Gordon equation, with the formal solution according to Green formula. Thirdly, boundary values are retrieved by solving the optimal problem which is constructed according to the best approximation between formal solutions and high-accuracy measurements in the interior of the domain. Finally, the assimilation problem is solved on substituting the retrieved boundary values into the Klein-Gordon equation. It is a type of inverse problem in mathematics. The advantage of this method lies in that it overcomes the inherent instability of the inverse problem of Fredholm integral equation and alleviates the error introduced by artificial boundary condition in data fusion using variational method in the past. 相似文献
8.
Sensitivity simulations are conducted in AREM (Advanced Regional Eta-Coordinate numerical heavy-rain prediction Model) for a torrential precipitation in June 2008 along South China to investigate the effect of initial uncertainty on precipitation predictability. It is found that the strong initial-condition sensitivity for precipitation prediction can be attributed to the upscale evolution of error growth. However, different modality of error growth can be observed in lower and upper layers. Compared with lower-level, significant error growth in the upper-layer appears over both convective area and high jet stream. It thus indicates that the error growth depends on both moist convection due to convective instability and the wind shear associated with dynamic instability. As heavy rainfall process can be described as a series of energy conversion, it reveals that the advection-term and latent heating serve as significant energy sources. Moreover, the dominant source terms of error-energy growth are nonlinearity advection (ADVT) and difference in latent heating (DLHT), with the latter being largely responsible for the rapid error growth in the initial stage. In this sense, the occurrence of precipitation and error-growth share the energy source, which implies the inherent predictability of heavy rainfall. In addition, a decomposition of ADVT further indicates that the flow-dependent error growth is closely related to the atmospheric instability. Thus the system growing from unstable flow regime has its intrinsic predictability. 相似文献
9.
The free Rossby wave (RW) solutions in an ocean with a straight coast when the offshore wavenumber of incident (l1) and reflected (l2) wave are equal or complex are discussed. If l1 = l2 the energy streams along the coast and a uniformly valid solution cannot be found; if l1,2 are complex it yields the sum of an exponentially decaying and growing (away from the coast) Rossby wave. The channel does not admit these solutions as free modes.If the wavenumber vectors of the RWs are perpendicular to the coast, the boundary condition of no normal flow is trivially satisfied and the value of the streamfunction does not need to vanish at the coast. A solution that satisfies Kelvin's theorem of time-independent circulation at the coast is proposed.The forced RW solutions when the ocean's forcing is a single Fourier component are studied. If the forcing is resonant, i.e. a free Rossby wave (RW), the linear response will depend critically on whether the wave carries energy perpendicular to the channel or not. In the first case, the amplitude of the response is linear in the direction normal to the channel, y, and in the second it has a parabolic profile in y. Examples of these solutions are shown for channels with parameters resembling the Mozambique Channel, the Tasman Sea, the Denmark Strait and the English Channel. The solutions for the single coast are unbounded, except when the forcing is a RW trapped against the coast. If the forcing is non-resonant, exponentially decaying or trapped RWs could be excited in the coast and both the exponentially “decaying” and exponentially “growing” RW could be excited in the channel. 相似文献
10.
Y. -L. Lin 《Meteorology and Atmospheric Physics》1996,59(3-4):153-172
Summary The nonlinear response of a dynamically unstable shear flow with critical level to an initial temperature anomaly is investigated using a nonlinear numerical model. Both nonconstant and constant shear profiles of the basic flow are considered. Effects of the solid lower boundary on the dynamically unstable, nonlinear flow are also studied. It is found that in a dynamically unstable, linear flow with a hyperbolic tangent wind profile, the updraft is tilted upshear. The result in consistent with that of a linear stability model (LC). The upshear tilt can be explained by the Orr mechanism (1907) and the energy argument proposed by LC. In a dynamically unstable, nonlinear flow, the updrafts produced by a sinusoidal initial temperature perturbation are stronger in the lower layer and are more compact and located further apart compared to the corresponding linear flow. In addition, the perturbed wave energy is slightly smaller than the linear case. It is found that the growth rate is smaller during the early stage and much larger during the later stage. For a localized initial temperature perturbation in a dynamically unstable flow, a stronger updraft with two compensated downdrafts are produced. Gravity waves are produced in a dynamically stable flow with both a hyperbolic tangent wind profile and a linear wind profile. For a linear shear flow with Richardson number less than 1/4, the disturbance grows in the early stage and then decays algebraically at later times, similar to that found in other linear theoretical studies. The influence of the solid lower boundary is to suppress the shear instability in a nonlinear flow with a hyperbolic tangent wind profile ofRi<1/4.With 9 Figures 相似文献
11.
湿层结参数非常数时雨团模型中的位势不稳定 总被引：1，自引：0，他引：1
建立了圆柱坐标下湿层结参数在垂直方向不为常数时的非轴对称雨团数学模型,着重讨论了其中的位势不稳定问题。抽象出了暴雨发生前期、盛期和发生后的三种典型湿层结参数的垂直分布。得到了此时位势不稳定的判据,分别给出了不稳定扰动增长率与稳定扰动振荡圆频率的上、下界。并在该参数取分2段常数的情况下,进行了解析求解。得到以下结论:该模型雨团在水平方向可有螺旋结构,这与用雷达资料得到的实际情况一致。在暴雨发生前期,有位势不稳定发生;且螺旋臂条数越多,雨团半径越小,不稳定增长率的上界越大。在暴雨盛期,整层为弱位势稳定层结,无位势不稳定发生;扰动螺旋臂条数越少,半径越大,其振荡圆频率下界越大。在暴雨结束后,整层为强位势稳定层结,也无位势不稳定发生;扰动螺旋臂条数越多,半径越小,其振荡圆频率的上界越大。在该参数取为2段常数情况下,且下层与上层其分别为负、正值时,有位势不稳定发生,且雨团的螺旋臂越多、半径越小及不稳定层次越厚,其增长率越大。该不稳定雨团的垂直结构在下层大体为半个正弦波,波长随不稳定层次的增厚而增大;在上层则为指数分布,且随高度增加迅速趋于0。 相似文献
12.
利用T63L9全球谱模式和NCEP/NCAR再分析资料, 对BGM方法中增长模的繁殖长度对集合预报效果的影响进行研究。结果表明:与控制预报相比, 不同繁殖长度的集合预报都能使预报效果得到一定程度的改进, 特别是第4天预报以后, 改进程度随预报时效而稳步提高。三组不同繁殖长度的集合预报对控制预报的改进存在差别, 分析结果表明:繁殖长度为2 d的集合预报明显效果最差, 而繁殖3 d和4 d的集合预报差别并不明显。对集合Talagrand分布以及离散度的初步分析表明, 繁殖长度取为3 d似乎最为合理。 相似文献
13.
A class of non-linear instabilities of a vertically sheared zonal flow is discussed. This is a type of baroclinic instability that lies outside the purview of a linear eigenmode analysis of baroclinic instability problems. The form taken by the instability is that of an ensemble of three neutral Rossby waves whose amplitudes are slowly modified by their mutual non-linear interactions. For a triad of small amplitude, these interactions introduce a weak, vertical variation of phase to the structure of the individual waves. This allows the generation of rectified heat fluxes and an exchange of energy with the mean flow.This instability exhibits explosive growth and spans a range of horizontal wavenumbers that exceeds the range that is unstable in the corresponding linear model. It is shown that the type of instability discussed can only occur when the model used admits unstable eigenmodes as well as neutral Rossby waves.The mechanism for the non-linear instability discussed here is believed to be fairly general and should exist also in the context of a horizontally sheared flow where it would take the form of a barotropic instability. 相似文献
14.
The Spatial Patterns of Initial Errors Related to the ＂Winter Predictability Barrier＂ of the Indian Ocean Dipole 
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下载免费PDF全文 In this study, using the Geophysical Fluid Dynamics Laboratory Climate Model version 2pl （GFDL CM2pl） coupled model, the winter predictability barrier （WPB） is found to exist in the model not only in the growing phase but also the Indian Ocean dipole （IOD） decaying phase of positive events due to the effect of initial errors. In particular, the WPB is stronger in the growing phase than in the decaying phase. These results indicate that initial errors can cause the WPB. The domi- nant patterns of the initial errors that cause the occurrence of the WPB often present an eastern-western dipole both in the surface and subsurface temperature components. These initial errors tend to concentrate in a few areas, and these areas may represent the sensitive areas of the predictions of positive IOD events. By increasing observations over these areas and eliminating initial errors here, the WPB phenomenon may be largely weakened and the forecast skill greatly improved. 相似文献
15.
《Dynamics of Atmospheres and Oceans》2005,40(3):151-162
An asymptotic solution of inviscid Boussinesq equations for a ‘dry convective Rankine vortex’ with prescribed buoyant forcing is given. The obtained vortex solution demonstrates monotonic growth with height of the vortex core radius, which becomes infinite at a certain critical altitude, and the corresponding attenuation of the vertical vorticity. This idealized vortex is then embedded in a convectively unstable boundary layer; the resulting approximate vortex solution has been applied to determine the maximum rotational wind speed and diameter of dry convective dust-devil-like vortices. 相似文献
16.
对由具有模糊值损益证券所构成市场中的期望效用优化问题进行了分析.在分析中使用了加权期望效用模型度量模糊值财富对应的期望效用,提出了模糊意义下的套利概念,证明了最优投资组合存在当且仅当市场不存在模糊意义下的套利机会,重点讨论了最优投资组合的性质,并利用最优组合描述了资产的当前价格. 相似文献
17.
Summary Response of the atmosphere to a line-type heat sink, which represents a cold pool induced by evaporative cooling in falling precipitation, is investigated. Two-dimensional, steady-state, linear perturbations forced by the diabatic cooling in the presence of a critical level are solved analytically. The ambient flow is assumed to have a three-layer structure which is the same as that in Lindzen and Tung (1976, denoted as LT hereafter) except that an isolated diabatic cooling is specified in the lower layer. The shear layer with a critical level is assumed to be either dynamically stable or unstable. A steady-state solution is possible even for a dynamically unstable flow in the middle layer because the wave energy is allowed to propagate to infinity in the upper layer.Thermally induced wave response near the critical level depending on the stability and wind shear in terms of the Richardson number exhibits the same behavior as the eigenvalue problem solved by Jones (1967) and LT because the source mechanism does not change the critical level behavior. That is, when the shear layer is dynamically stable, almost all of the wave energy is absorbed near the critical level, while for dynamically unstable case waves can be partially-or over-reflected from the critical level depending on the Richardson number. Waves can be over-reflected and over-transmitted simultaneously as they travel through the critical level in the process of the energy extraction from the unstable mean shear flow.Using the duct condition proposed by LT, it is found that the magnitude of the perturbation vertical velocity in the lower layer is 6 times larger than that for a nonducting case with the same cooling rate. This implies that under a proper choice of the critical level height and stability profile, the response of the atmosphere to a line-type heat sink can be significantly enhanced through the over-reflection process.With 7 Figures 相似文献
18.
While recent observational studies have shown the critical role of atmospheric transient eddy (TE) activities in midlatitude unstable air-sea interaction, there is still a lack of a theoretical framework characterizing such an interaction. In this study, an analytical coupled air-sea model with inclusion of the TE dynamical forcing is developed to investigate the role of such a forcing in midlatitude unstable air-sea interaction. In this model, the atmosphere is governed by a barotropic quasi-geostrophic potential vorticity equation forced by surface diabatic heating and TE vorticity forcing. The ocean is governed by a baroclinic Rossby wave equation driven by wind stress. Sea surface temperature (SST) is determined by mixing layer physics. Based on detailed observational analyses, a parameterized linear relationship between TE vorticity forcing and meridional second-order derivative of SST is proposed to close the equations. Analytical solutions of the coupled model show that the midlatitude air-sea interaction with atmospheric TE dynamical forcing can destabilize the oceanic Rossby wave within a wide range of wavelengths. For the most unstable growing mode, characteristic atmospheric streamfunction anomalies are nearly in phase with their oceanic counterparts and both have a northeastward phase shift relative to SST anomalies, as the observed. Although both surface diabatic heating and TE vorticity forcing can lead to unstable air-sea interaction, the latter has a dominant contribution to the unstable growth. Sensitivity analyses further show that the growth rate of the unstable coupled mode is also influenced by the background zonal wind and the air–sea coupling strength. Such an unstable air-sea interaction provides a key positive feedback mechanism for midlatitude coupled climate variabilities.
相似文献19.
海气相互作用与年代际气候振荡可能机制初探 总被引：2，自引：2，他引：2
从简单海气相互作用方程组出发，引进新的海洋对大气加热函数，得到简单海气相互作用方程组的解析解。解析解表明，海气相互作用可以产生不稳定耦合波，这种波的不稳定程度随海气相互作用系数和深海对海洋混合层的影响而不同，并且e-折时间尺度随海气相互作用系数出现极小值，这个极小值点对应的周期是最不稳定海气耦合波的周期；海气相互作用产生的最不稳定海气耦合波的周期在中纬度地区是18a，在低纬度是3．5a，在高纬度是35a，它可能是海气系统年代际振荡的机制之一。 相似文献
20.
利用湖北咸宁站2008年6月1日—2012年8月1日地基微波辐射计观测数据反演的相对湿度、大气液态水含量、大气水汽总量、大气层结曲线,对比分析了短时暴雨与一般降水过程发生前微波辐射计观测资料反映的特征,研究微波辐射计观测资料在短时暴雨潜势预报中的应用。结果表明:当大气液态水含量从1 mm左右急增至约20 mm、大气水汽总量从60~70 mm急增到90 mm以上之后,如果0~6 km整层相对湿度均接近饱和或达到饱和状态,且在800~950 hPa附近存在逆温层,最大K指数超过35℃,最大TT指数 (Thei-Tornqvist指数) 达到或超过40℃,那么未来3 h或6 h内发生短时暴雨的几率大。 相似文献