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81.
WANG Bin LIU Juanjuan WANG Shudong CHENG Wei LIU Juan LIU Chengsi Qingnong XIAO Ying-Hwa KUO 《大气科学进展》2010,27(4):715-727
Four-dimensional variational data assimilation (4DVar) is one of the most
promising methods to provide optimal analysis for numerical weather
prediction (NWP). Five national NWP centers in the world have successfully
applied 4DVar methods in their global NWPs, thanks to the increment method
and adjoint technique. However, the application of 4DVar is still limited by
the computer resources available at many NWP centers and research
institutes. It is essential, therefore, to further reduce the computational
cost of 4DVar. Here, an economical approach to implement 4DVar is proposed,
using the technique of dimension-reduced projection (DRP), which is called
``DRP-4DVar." The proposed approach is based on dimension reduction using
an ensemble of historical samples to define a subspace. It directly obtains
an optimal solution in the reduced space by fitting observations with
historical time series generated by the model to form consistent forecast
states, and therefore does not require implementation of the adjoint of
tangent linear approximation.
To evaluate the performance of the DRP-4DVar on assimilating different types
of mesoscale observations, some observing system simulation experiments are
conducted using MM5 and a comparison is made between adjoint-based 4DVar and
DRP-4DVar using a 6-hour assimilation window. 相似文献
82.
In a two-dimensional and linear framework, a transformation was developed to derive eigensolutions of internal waves over a subcritical hyperbolic slope and to approximate the continental slope and shelf. The transformation converts a hyperbolic slope in physical space into a flat bottom in transform space while the governing equations of internal waves remain hyperbolic. The eigensolutions are further used to study the evolution of linear internal waves as it propagates to subcritical continental slope and shelf. The stream function, velocity, and vertical shear of velocity induced by internal wave at the hyperbolic slope are analytically expressed by superposition of the obtained eigensolutions. The velocity and velocity shear increase as the internal wave propagates to a hyperbolic slope. They become very large especially when the slope of internal wave rays approaches the topographic slope, which is consistent with the previous studies. 相似文献
83.
In this paper, we analyze the effects of radiative cooling on the pure baroclinic low-frequency waves under the approximation of equatorial β-plane and semi-geostrophic condition. The results show that radiative cooling does not, exclusively, provide the damping effects on the development of low-frequency waves.Under the delicate radiative-convective equilibrium, radiative effects will alter the phase speed and wave period,and bring about the broadband of phase velocity and wave period by adjusting the vertical profiles of diabaticheating. When the intensity of diabatic heating is moderate and appropriate, it is conductive to the development and sustaining of the low-frequency waves and their broadband phenomena, not the larger, the better. The radiative cooling cannot be neglected in order to reach the moderate and appropriate intensity of diabatic heating. 相似文献
84.
85.
为研究在厄尔尼诺现象演变过程中海气相互作用的性态特征,该文再次应用拓展伴随模态分析于简易海洋同化数据(SODA data).结果表明:通过相互作用形成厄尔尼诺/拉尼娜现象的海洋与大气具有明显不同的性态,气候系统中并不存在一个相对独立的热带太平洋大气变异,但是的确存在一个相对独立的热带太平洋海洋变异;原因在于大气是底部界面受热而海洋是顶部界面受热,从而导致前者具有较后者强烈得多的斜压不稳定性和能够覆盖大部分热带太平洋的赤道辐合带; 再次证实了正是直接来自中纬度海域的西风爆发和海面风辐聚导致赤道太平洋上层海水的东向移动和经向辐聚造就了厄尔尼诺所特有的增温信号. 相似文献
86.
Oceanic turbulence measurements made by an acoustic Doppler velocimeter (ADV) suffer from noise that potentially affects the estimates of turbulence statistics. This study examines the abilities of Kalman filtering and autoregressive moving average models to eliminate noise in ADV velocity datasets of laboratory experiments and offshore observations. Results show that the two methods have similar performance in ADV de-noising, and both effectively reduce noise in ADV velocities, even in cases of high noise. They eliminate the noise floor at high frequencies of the velocity spectra, leading to a longer range that effectively fits the Kolmogorov ?5/3 slope at mid-range frequencies. After de-noising adopting the two methods, the values of the mean velocity are almost unchanged, while the root-mean-square horizontal velocities and thus turbulent kinetic energy decrease appreciably in these experiments. The Reynolds stress is also affected by high noise levels, and de-noising thus reduces uncertainties in estimating the Reynolds stress. 相似文献
87.
Near-bottom currents play important roles in the formation and dynamics of deep-water sedimentary systems.This study examined the characteristics and temporal variations of near-bottom currents, especially the tidal components, based on two campaigns(2014 and 2016) of in situ observations conducted southeast of the Dongsha Island in the South China Sea. Results demonstrated near-bottom currents are dominated by tidal currents, the variance of which could account for ～70% of the total current variance. Diurnal tidal currents were found stronger than semidiurnal currents for both barotropic and baroclinic components. The diurnal tidal currents were found polarized with predominantly clockwise-rotating constituents, whereas the clockwise and counterclockwise constituents were found comparable for semidiurnal tidal currents. It was established that diurnal tidal currents could induce strong current shear. Baroclinic tidal currents showed pronounced seasonal variation with large magnitude in winter and summer and weak magnitude in spring and autumn in 2014. The coherent components accounted for ～65% and ～50% of the diurnal and semidiurnal tidal current variances,respectively. The proportions of the coherent and incoherent components changed little in different seasons. In addition to tidal currents, it was determined that the passing of mesoscale eddies could induce strong nearbottom currents that have considerable influence on the deep circulation. 相似文献
88.
建立南海潮波模式及其伴随同化模式,在传统二维潮波方程的基础上加入了内潮耗散项,考虑了内潮耗散对南海潮波系统的影响,在前人工作基础上,改进了内潮耗散参数化方案,并给出内潮耗散项中地形效应参数的计算公式;通过对比,本文的参数化方案比前人参数化方案能取得更为合理的模拟结果。以63个验潮站和24个TOPEX/Poseidon卫星高度计轨道交叉点处的调和常数作为观测值,利用伴随同化方法来优化模式中的底摩擦系数和内潮耗散系数。为了寻求最优的优化方案,设计了7组数值实验。实验结果表明,实验7先优化内潮耗散系数再优化底摩擦系数的模拟结果最优。利用实验7的模拟结果分析了南海M2分潮的潮波特征,与前人结果基本一致。 相似文献
89.
A coastline is defined as the average spring tide line. Different types of seacoast, such as sandy, silty, and bio- logical coast, have different indicators of interpretation. It is very difficult to develop a universal method for interpreting all shorelines. Therefore, the sandy, the silty, and the biological coast are regarded as research objects, and with data mining technolog,found the rules of interpretation of those three types of coastlines. Then, an intelligent coastline interpretation method based on rules was proposed. Firstly, the rules for ex- tracting the waterline in Landsat TM/ETM＋ （Thematic Mapper/Enhanced Thematic Mapper Plus） imagery were discovered. Then, through analyzing the features of sandy, silty and biological coast, the indicators of interpreting different types of shoreline were determined. According to the indicators, the waterline could be corrected to the real coastline. In order to verify the validity of the proposed algorithms, three Landsat TM/ETM＋ imageries were selected for case studies. The experimental results showed that the proposed methods could interpret the coastlines of sandy; silty, and biological coasts with high precision and without human intervention, which exceeded three pixels. 相似文献
90.