北大西洋涛动位相转换的数值研究

A Numerical Study of the Phase Transition of the North Atlantic Oscillation

借助一个非线性准地转正压模型,模拟了基本西风气流的强弱、不同空间分布的天气尺度扰动涡对北大西洋涛动(NAO)位相转换的作用,以及大尺度双波地形对其的影响。通过一系列的对比试验发现,适当弱的基本西风气流有利于下游系统西退使NAO由正(负)位相转换为负(正)位相;振幅强、活动范围大的天气尺度扰动波是NAO由负位相转换为正位相的有利条件,而加强并向北移的天气尺度扰动波是NAO由正位相转换为负位相的有利条件;叠加上大尺度双波地形后,NAO由正(负)位相转换为负(正)位相的个例数减少。

using a nonlinear quasi-geostrophic barotropic model, the paper investigates numerically how the spatial pattern of synoptic scale waves and the westerly wind strength affect the phase transition of the North Atlantic Oscillation （NAO）, and the role played by the large-scale topography. It is found that the weak basic westerly wind is favorable for the westward shift of the downstream large-scale system, favoring the transition of the NAO from positive （negative） phase into negative （positive） phase. It is noted that when the synoptic scale waves are stronger and concentrated in a wider region, the NAO event can transform more easily from the negative phase into positive phase; when the synoptic scale waves are stronger and shift northward, the NAO can transform more easily from the positive into negative phase. In the presence of a large scale topography, the number of the cases in which the NAO transforms from positive （negative） phase to negative （positive） phase is reduced.