LATTICE BOLTZMANN EQUATION MODEL IN THE CORIOLIS FIELD

In a large-scale field of rotational fluid, various unintelligible and surprising dynamic phenomena are produced due to the effect of the Coriolis force. The lattice Boltzmann equation (LBE) model in the Coriolis field is developed based on previous works.^[1-4] Geophysical fluid dynamics equations are derived from the model. Numerical simulations have been made on an ideal atmospheric circulation of the Northern Hemisphere by using the model and they reproduce the Rossby wave motion well. Hence the applicability of the model is verified in both theory and experiment.     

一个完全守恒的格子Boltzmann模型

利用六角形格子离散的方法,使得每个六角形Cell里含有 3种不同运动速度的粒子微团,宏观物理量用这些粒子微团的矩来定义.根据微观和宏观之间的质量、动量、能量守恒准则,建立了一个二维的D2Q19格子Boltzmann模型,从该D2Q19模型出发可推导出宏观的流体力学方程组.用该模型对冲击波在障碍物组表面上的折射现象进行数值模拟,并将计算结果与实验进行了比较.     

Actual Tropical Waves Identified by the Wavenumber-Frequency Spectrum Analysis during Boreal Summer

Based on daily satellite-observed outgoing longwave radiation （OLR） data, the tropical intraseasonal oscillation （ISO） associated with the Asian summer monsoon is found to be dominant during the 2005 summer. Such an ISO along with other tropical waves are identified using a wavenumber-frequency spectrum analysis. Some of Significant spectral peaks coincide well with the dispersion curves of the equatorially trapped wave modes from shallow＇water theory, with various equivalent depths of 12-200 m, suggesting that actual tropical waves can be detected from observational data. Although the formation mechanism of the ISO is more complicated than those of other tropical waves with higher frequencies, significant spectral peaks that correspond to the ISO with a period of 30-60 days distinctly appear in the OLR spectra. The selective wavenumber-frequency filtering of OLR data is thus performed to isolate the ISO, Kelvin and equatoriai Rossby waves, and the properties and signatures of such tropical waves that control tropical atmospheric variability for the 2005 summer are clearly identified.