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1.
A three-dimensional(3D) global adiabatic spectral primitive equation model has been designed.The main features are as follows.(1) Adoption of spherical harmonics and Tschebyscheff polynomials as the basis functions in the horizontal and vertical respectively,but the unknowns in the spectral equations are two-dimensional;(2) Inclusion of the tropopause,which may vary with time and space;(3) Suggestion of a spectral method for representing the vertical structure of the atmosphere applicable to the unsmoothed profile case;(4) In consideration of nonlinear vertical aliasing a technique is proposed to avoid it and nonlinear computational instability.Based on real data forecasts up to 48 hours have been performed.The results show that the statistical verifications with the model are superior on the average to those with the T42L9 used operationally before 1995 at NMC of China at the same mean resolution. 相似文献
2.
设计了适用于四维变分同化系统的扰动预报模式GRAPES_PF。根据GRAPES的地形追随坐标非静力原始方程组,采用小扰动分离方法推导微分形式的线性扰动预报方程组,并利用与GRAPES非线性模式相似的数值求解方案求解线性扰动微分方程组。在设计扰动预报模式时采用了两个时间层半隐式半拉格朗日方案对动量方程、热力学方程、水汽方程和连续方程进行时间差分,空间差分方案的变量分布水平方向采用Arakawa C跳点网格,垂直方向采用Charney/Phillips跳层。利用代数消元法进一步推导得到只包含未来时刻扰动Exner气压的亥姆霍兹方程,进而通过广义共轭余差法（GCR）求解,在此基础上得到未来时刻扰动量的预报值。基于所开发的扰动模式开展了数值试验。首先在非线性模式中施加一个中尺度初始扰动高压,得到初始扰动在非线性模式中的后续演变,然后将相同的初始扰动作为扰动模式的初值进行时间积分,将扰动模式预报的结果与非线性模式的结果做了对比。结果表明,所开发的扰动模式GRAPES_PF较好地模拟了惯性重力内波的传播过程:初始高压扰动激发了一个迅速向外传播的惯性重力内波,在气压场向风场适应的过程中,水平风场、垂直运动、位温和湿度等变量均出现了扰动增量,与非线性模式得到的结果相当接近。GRAPES_PF作为GRAPES非线性模式的合理线性模式为建立基于线性扰动预报的区域四维变分同化系统奠定了科学基础。 相似文献
3.
Yan Zhihui Guo Xiaorong Zheng Guoan Zhu Qi Zhang Yuling 《Acta Meteorologica Sinica》1996,10(3):295-308
The limited area analysis and forecast system(LAFS)was developed and has been put intooperational use at National Meteorological Center since January 1991.This system can be regardedas a branch system attached to the global assimilation and medium-range forecast system which isbased on a spectral model T42L9.The main advancements as an upgrade operational system are asfollows:the use of a regional fine mesh optimum interpolation(OI)analysis scheme:the realiza-tion of the nonlinear normal mode initialization for the regional model:the development of a 15L-spherical grid primitive equation model(with real topography and enstrophy conservation)and itsnesting forecast with the spectral model T42L9. 相似文献
4.
The interaction of an internal wave beam (IWB) with an idealized oceanic pycnocline is examined using two-dimensional fully nonlinear direct numerical simulations based on a spectral multidomain penalty method in the vertical direction. The phenomenon of focus is the nonlinear generation of harmonics. A total of 24 simulations have been performed, varying the normalized pycnocline thickness and the ratio of peak pycnocline Brunt-Väisälä frequency to that of the stratified lower layer. Harmonics at the point of IWB entry into the pycnocline increase in amplitude and number with a measure of the maximum gradient of the Brunt-Väisälä frequency, suggesting refraction as an important factor in harmonic generation. Among the simulations performed, two distinct limits of pycnocline thickness are identified. For thin pynoclines, whose thickness is 10% of the incident IWB's horizontal wavelength, harmonics trapped within the pycnocline have maximum amplitude when their frequency and wavenumber match those of the natural pycnocline interfacial wave mode. Results in this case are compared with weakly nonlinear theory for harmonic generation by plane wave refraction. For thicker pycnoclines, whose thickness is equal the incident IWB's horizontal wavelength, IWB refraction results in harmonic generation at multiple locations in addition to pycnocline entry, giving rise to complex flow structure inside the pycnocline. 相似文献
5.
There are two important features in geophysical fluid dynamics. One is that the atmospheric and oceanic equa-tions of motion include the Coriolis force; another is that they describe a stratified fluid. The hydrostatic extraction scheme, or standard stratification approximation, posed by Zeng (1979), reflects the second aspect of geophysical flu-id dynamics. There exist two major advantages in this scheme; accurate computation of the pressure gradient force can be obtained over steep mountain slopes, and the accumulation error in vertical finite differencing can be reduced, especially near the tropopause.Chen et al (1987) introduced the hydrostatic extraction scheme into a global spectral model, which attained pre-liminary success at low resolution. Zhang and Sheng et al (1990) developed and improved the hydrostatic extraction scheme in a global spectral model, in which C0, the parameter that represents the stratification of the reference at-mosphere, changes not only with height, but also with latitude. The scheme has been incorporated BMRC’s global spectral model (IAPB). Four 5-day forecasts have been performed to test the IAPB with the hydrostatic extraction scheme. Objective verifications demonstrate a positive effect of the hydrostatic extration scheme on BMRC’s model, particularly at upper levels, over the tropics and the Antartic region. 相似文献
6.
Plumb三维波作用通量和EP剖面图——对定常波模式输出结果的诊断分析 总被引：1，自引：0，他引：1
雷兆崇 《南京气象学院学报》1991,(1)
本文利用Plumb(1985年)所导出的线性、准地转定常波的三维波作用通量和Eliassen-Palm(EP)剖面图,对于一个线性和一个非线性的关于大气定常波的斜压初始方程三维谱模式的若干输出结果进行了诊断分析。分析结果表明,Plumb通量和EP剖面图,不仅可以用来诊断波作用在三维空间的传播、波动与纬向平均气流之间的相互作用,而且也可以用来诊断非线性作用的显著性,在利用它们对于观测资料进行诊断分析时,应当充分注意到非线性作用的影响。 相似文献
7.
Structures of adjoint sensitivities to potential vorticity for specific initial and final norm are investigated for a short-range cyclone forecast in a three-dimensional quasigeostrophic (QG) model. Moreover, adjoint sensitivities to potential vorticity are compared with nonlinear sensitivities calculated for the same cyclogenesis case in the QG model. The adjoint sensitivities using different initial and final norms (e.g., total QG disturbance energy and potential enstrophy) show approximately similar characteristics for the horizontal and vertical structures and evolutions. Consistent with previous studies, the horizontal structure of the adjoint sensitivity is smaller for the energy norm than for the potential enstrophy norm. The dynamical mechanism of cyclone development by adjoint sensitivity coincides with that of nonlinear sensitivity, with slight differences in the region of sensitivity maxima over the upstream (nascent) low for the adjoint (nonlinear) sensitivity. The adjoint sensitivities show different vertical distributions from the nonlinear sensitivities. Consistent with the sensitive regions denoted by singular vectors and error evolution in the QG model, maxima of the adjoint sensitivities are located at both the upper and lower boundaries, with prominent secondary peaks in the lower to mid-troposphere of the domain. The level of the secondary maxima changes depending on the initial and final norm used. The secondary peak is located in the lower to mid- (mid-) troposphere for the total QG disturbance energy (potential enstrophy) as the initial and final norm. Based on the correspondence in the level of the sensitivity maxima in the interior of the domain between the adjoint and nonlinear sensitivities, adjoint sensitivities may serve as an alternative to nonlinear sensitivities given the enormous computing expenses in nonlinear sensitivity calculation. 相似文献
8.
北半球七层原始方程谱模式ff考虑了较完整的物理过程:（1）地形作用（采用了σ坐标系）和地面摩擦；（2）动量、热量，水汽的水平扩散过程和垂直扩散过程（其中包括了下垫面感热和水汽作用）；（3）水汽凝结潜热作用；（4）云和辐射作用；（5）积云对流过程等。上述模式采用了非线性平衡方程初值化方法。并利用逐日客观分析资料，制作5天中期数值预报试验。本文给出了1982年冬季和夏季的20个例子的五天数值预报验证结果和一个例子的中期数值预报图和对应的实况图。预报效果比较好。在数值预报试验中，虽然纬向波数只取15个波，但所取得的短期、中期的预报效果能和一些较高分辨率模式的预报效果相比较。 相似文献
9.
A strategy for evaluating a global shallow water model based on aspects of kinetic energy spectra and nonlinear vorticity dynamics is proposed in this study. The kinetic energy spectra and nonlinear vorticity dynamics of a recently developed global shallow water model on an unstructured mesh are evaluated in comparison with the benchmark solutions from a global high-resolution spectral model. The results show that the kinetic energy spectra, the rotational and divergent components, the stationary and transient components, and the nonlinear spectral fluxes of the developed shallow water model agree well with those generated by the reference model. In addition, the influence of different flux operators for transporting the potential vorticity(PV) is assessed specifically. It is indicated that the second-order flux operator leads to a spurious increase in the kinetic energy at the tail of the spectrum, whereas the upwind third-order flux operator does not support this behavior owing to implicit numerical diffusion. Moreover, the nonlinear vorticity dynamics is studied by using colliding modons. It is found that the grid-point model maintains the symmetrical pattern of vortices, and generates similar kinetic energy spectra and nonlinear spectral fluxes to the reference model. The evaluation provides a reference for assessing the shallow water model in terms of nonlinear dynamics, and the developed global shallow water model presents a good example. 相似文献
10.
针对GRAPES四维变分同化系统的升级, 研究了GRAPES模式垂直扩散方案线性化问题。通过2005年8月7—27日21个个例的批量试验, 发现在GRAPES模式垂直扩散方案源代码的基础上逐句线性化得到的切线性垂直扩散方案即使能通过正确性测试试验, 在少数情况下也会存在很大误差。切线性模式计算的扰动气压场和扰动风场可能出现明显异常, 这种异常与垂直扩散方案中地表动量通量的强非线性有关。如果在切线性垂直扩散方案中忽略地表动量通量扰动, 既可以避免异常的出现, 又不影响其他正常时刻的计算精度。修改后的切线性垂直扩散方案能够在所有变量上一致地提高切线性模式的计算精度。 相似文献
11.
An analysis is made of the effects of topography on the summer atmospheric energetics of the Northern Hemisphere in a low-resolution global spectral model. The numerical model is a global, spectral, primitive equation model with five equally spaced sigma levels in the vertical and triangular truncation at wavenumber 10 in the horizontal. The model includes comparatively full physical processes.Each term of the energy budget equations is calculated in four specific latitudinal belts (81.11°S-11.53°S; 11.53°S-11.53°N; 11.53°N-46.24°N; 46.24°N-81.11°N) from a five-year simulation with mountains and a one-year simulation without mountains, respectively. Differences between them are compared and statistically tested. The results show that synoptical scale waves transport available potential energy and kinetic energy to long waves and increase conversion from available potential energy of the zonal flow to eddy’s and from the eddy kinetic energy to the zonal kinetic energy in region 3 (11.53°N-46.24°N) due to mountains; topography intensifies the atmospheric baroclinity in region 3, consequently the baroclinic conversion of atmosphere energy is increased. The seasonal characteristics associated with the summer atmospheric energy source in region 3 are caused by seasonal variation of the solar radiation and the land-ocean contrasts and independent of topographic effects. The mechanism of topographic effects on the increase of long wave kinetic energy is also discussed. 相似文献
12.
An investigation into high Reynolds number turbulent flow over a ridge top in New Zealand is described based on high-resolution
in-situ measurements, using ultrasonic anemometers for two separate locations on the same ridge with differing upwind terrain
complexity. Twelve 5-h periods during neutrally stratified and weakly stable atmospheric conditions with strong wind speeds
were sampled at 20 Hz. Large (and small) turbulent length scales were recorded for both vertical and longitudinal velocity
components in the range of 7–23 m (0.7–3.3 m) for the vertical direction and 628–1111 m (10.5–14.5 m) for the longitudinal
direction. Large-scale eddy sizes scaled to the WRF (Weather Research and Forecasting) numerical model simulated boundary-layer
thickness for both sites, while small-scale turbulent features were a function of the complexity of the upwind terrain. Evidence
of a multi-scale turbulent structure was obtained at the more complex terrain site, while an assessment of the three-dimensional
isotropy assumption in the inertial subrange of the spectrum showed anisotropic turbulence at the less complex site and evidence
of isotropic turbulence at the more complex site, with a spectral ratio convergence deviating from the 4/3 or unity values
suggested by previous theory and practice. Existing neutral spectral models can represent locations along the ridge top with
simple upwind complexity, especially for the vertical wind spectra, but sites with more orographic complexity and strong vertical
wind speeds are often poorly represented using these models. Measured spectra for the two sites exhibited no significant diurnal
variation and very similar large-scale and small-scale turbulent length scales for each site, but the turbulence energy measured
by the variances revealed a strong diurnal difference. 相似文献
13.
气溶胶与云的垂直分布特征是气溶胶间接气候效应关注的重点。基于2018年7—8月华北中部6架次飞机观测数据,研究气溶胶和云滴的垂直和水平分布特征。结果表明:华北中部780~5687 m高度内气溶胶数浓度( Na )平均值为821.36 cm-3,最大量级可达到104 cm-3,云中气溶胶数浓度(Nacc)占总颗粒浓度的80%以上,表明细颗粒占大多数,气溶胶粒子算术平均直径( Dm )平均值为0.12~0.52 μm;大气层结对气溶胶垂直分布影响较大,逆温阻挡气溶胶垂直输送,高空(高度2000 m以上) Dm 的垂直分布受到相对湿度影响较大; Na 和 Dm 在垂直方向波动较大,水平方向波动较小;低层云中云滴数浓度(Nc)较大、液态水含量(L)较小,而中层和高层云中Nc较小、L较大,Nc和云滴有效半径(Re)的概率密度函数均为双峰型分布,L的概率密度函数为单峰型分布;气溶胶数浓度谱基本呈现多峰型分布,而云滴数浓度谱多呈现单峰型分布。 相似文献
14.
中国三峡地区汛期降水量的正态性研究 总被引：4，自引：0，他引：4
为了分析三峡地区降水量序列的正态性和谱结构,对降水量的常见各种变换进行试验性研究。试验包括单站降水量、降水量的平方根、立方根和Γ分布概率值等非线性变换,以及级别变换。研究区域多站平均降水量、区域降水量的主分量、区域降水量的非线性变换后的主分量和区域降水量的级别变换后的主分量等序列。研究发现三峡地区单站降水量的各种变换不改变序列原始谱结构,仅影响概率分布的偏度和峰度,使其较好地遵从正态分布,其中以Γ分布的变换以及级别变换在分布的偏度上为最好。 区域降水量的各种变换的综合指数(区域平均值和主分量)正态性及谱结构分析表明,除区域平均值变换后不改变原单站序列的谱结构外,主分量的综合指数能改变原单站序列的谱结构,同时也影响概率分布的偏度和峰度,使其能较好地遵从正态分布。其中以降水量的立方根和Γ分布概率变换以及级别变换,在分布的偏度上有较好的效果。 相似文献
15.
《Dynamics of Atmospheres and Oceans》2005,40(3):209-236
Recent advances in observational technology have led to a more detailed knowledge of the low-level flow in hurricanes. In particular, quasi-streamwise rolls on a variety of scales have been observed. Some of these rolls have radial wavelengths of 4–10 km, which is comparable to rolls associated with instabilities inherent to Ekman-type boundary layers.The evolution and stability of the swirling boundary layer underneath a hurricane-like vortex is studied using both a nonlinear model and linearized stability analysis. The nonlinear model is an axisymmetric model of incompressible fluid flow, which is used to simulate the development of boundary layers underneath vortices with hurricane-like wind profiles. Axisymmetric rolls appear in these boundary layers, which have some similarities to the observed rolls in hurricanes. The axisymmetric flow is also used as the basic-state for a linearized stability analysis. The analysis technique allows for arbitrary variation in the radial and vertical directions for both the basic-state flow and the perturbations. Thus, the strong radial variations and curvature effects common to strong vortices are part of the analysis. The analysis finds both symmetric and asymmetric instabilities that are similar to those in the nonlinear simulations and in observations. The instabilities acquire some of their energy from the vertical shear associated with a reversal of the radial inflow at the top of the boundary layer, and some of their energy from vertical shear of the azimuthal flow. The radial flow energy conversion tends to increase for flows with less inertial stability and for modes oriented across the low-level shear; the azimuthal flow conversion increases for larger inertial stability and for modes aligned with the low-level shear. 相似文献
16.
The paleoclimatic variability at frequencies ranging from 10–4 cycle per year (cpy) to 10–3 cpy is investigated using a set of three deep-sea cores from the Indian Ocean. Three frequency bands of high paleoclimatic variability are first defined using upper and lower limits of the significant spectral power concentrations: the bands are centered around the spectral maxima located at 10.3, 4.7, and 2.5 kyr. The localisation of spectral lines is then refined by high-resolution spectral analysis.Some of the resulting lines have frequencies which are close to those previously detected in other paleoclimatic records, including the precessional peak at 19 kyr. Additional lines are also in good correspondence with the response of a nonlinear climatic oscillator forced by insolation variations, including peaks at 13 kyr, 10.4 kyr and 9.4 kyr. This correspondence suggests orbital forcing. Moreover for the Indian Ocean which is influenced by the monsoon circulation, it is plausible that the precessional contribution of the forcing interact strongly with the precipitation-temperature feedback used in the model, thus emphasizing the nonlinearity of the response. 相似文献
17.
本文给出了一种求解非线性平衡方程的新的有效的方法及有关的数值试验结果。和以往的求解方法相比，本方法的优点是:收敛速度快，不需要冗长的迭代计算，也不需要对初始高度场的某些记录作修改，并能节省大量的计算时间。文中利用北半球七层原始方程谱模式，使用了1982年的客观分析资料，进行中期数值天气预报试验。试验结果表明，用非线性平衡方程初值化方法制作中期数值预报比其他的如线性平衡方程初值化方程的更佳。后者因去掉了非线性项的作用，天气系统的强度预报结果偏弱且偏平滑。 相似文献
18.
模式垂直分辨率对梅雨锋暴雨数值模拟的影响 总被引：4，自引：5，他引：4
利用中尺度数值模式MM5(V3),对2003年7月7日~8日发生在武汉地区的一次梅雨锋暴雨过程进行了数值模拟。采用经过简化处理的基于矢量模的双参数最优化处理方法,对模式大气进行了垂直分层。在水平分辨率不变的情况下,数值模式的垂直分层分别采用25层和36层进行了对比模拟试验。模拟结果表明,水平分辨率达到较高的精度后,粗的垂直分辨率会放大模式中地形的作用,造成数值模拟雨带落区的偏差;要得到比较好的模拟结果,需要相应的提高数值模式的垂直分辨率。水平分辨率与垂直分辨率的不协调,会在水平方向上产生虚假的重力波,影响数值模式的模拟结果。 相似文献
19.
本文采用七层初始方程谱模式，模拟在特定的海温异常的、不均匀的分布下对低纬大气环流的影响。本文研究得到如下结果:1. 积分七层初始方程谱模式可模拟出一个低纬沃克环流。2. 东太平洋出现异常暖海温时，积分96小时后产生一个对沃克环流的扰动。3. 扰动在东西向呈现上升与下沉运动相间的波列，并具有明显的西传现象。4. 东太平洋出现异常偏冷海温时，模拟结果与暖海温时类似，但扰动环流的垂直运动符号与其相反。5. 当东太平洋海温为正态分布时，仍然可以得到上述结果。 相似文献
20.
An analysis is made of the effects of topography on the summer atmospheric energetics of the Northern Hemisphere in a low-resolution
global spectral model. The numerical mode! is a global, spectral, primitive equation model with five equally spaced sigma
levels in the vertical and triangular truncation at wavenumber 10 in the horizontal. The model includes comparatively full
physical processes.
Each term of the energy budget equations is calculated in four specific latitudinal belts (81.11°S–11.53°S; 11.53°S–11.53°N;
11.53°N–46.24°N; 46.24°N–81.11°N) from a five-year simulation with mountains and a one-year simulation without mountains,
respectively. Differences between them are compared and statistically tested. The results show that synoptical scale waves
transport available potential energy and kinetic energy to long waves and increase conversion from available potential energy
of the zonal flow to eddy's and from the eddy kinetic energy to the zonal kinetic energy in region 3 (11.53°N-46.24°N) due
to mountains; topography intensifies the atmospheric baroclinity in region 3, consequently the baroclinic conversion of atmosphere
energy is increased. The seasonal characteristics associated with the summer atmospheric energy source in region 3 are caused
by seasonal variation of the solar radiation and the land-ocean contrasts and independent of topographic effects. The mechanism
of topographic effects on the increase of long wave kinetic energy is also discussed. 相似文献