Global and Regional Axial Ocean Angular Momentum Signals and Length-of-day Variations (1985-1996)
Global and Regional Axial Ocean Angular Momentum Signals and Length-of-day Variations (1985-1996)
复制标题
全球和区域轴向海洋角动量信号和日长变化（1985-1996）
DOI：
10.1029/1999jc000157
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发表时间：
2000
影响因子：
--
通讯作者：
D. Stammer
中科院分区：
文献类型：
--
作者：
R. Ponte;D. Stammer
海洋角动量M围绕极轴的变化与纬向流的波动(相对分量MR)和质量的纬向移动(行星分量MΩ)有关。1°海洋模式的输出用于计算1985年1月至1996年4月期间每隔5天一次的全球MR、MΩ和M时间序列。MR、MΩ和M的年周期大于半年周期，MΩ的幅值是MR的近两倍，存在季节周期的年际调制，但年际变化较弱。M的光谱在次季节为红色(ω−1和ω−2之间的背景斜率)，表示海洋上的外部扭矩为白色或蓝色的光谱。与以前的研究比较表明，相对于不稳定和其他快速海洋信号的内部来源，直接大气强迫在产生亚季节M信号方面的重要性。区域角动量估计表明，低纬地区的季节变率往往较大，但由于纬向流和质量变率的空间结构，存在许多局地极大值。在季节尺度上，纬度∼20°S-10°N对MΩ的贡献很大，而MR的信号可以追溯到南极绕极流输送和相关的环流。与大气和固体地球的类似时间序列相比，M的可变性较小，但海洋信号与大气-固体地球残留物显著相关，这意味着海洋对日长变化有可测量的影响。
Changes in ocean angular momentum M about the polar axis are related to fluctuations in zonal currents (relative component Mr) and latitudinal shifts in mass (planetary component MΩ). Output from a 1° ocean model is used to calculate global Mr, MΩ, and M time series at 5 day intervals for the period January 1985 to April 1996. The annual cycle in Mr, MΩ, and M is larger than the semiannual cycle, and MΩ amplitudes are nearly twice those of Mr. Year-to-year modulation of the seasonal cycle is present, but interannual variability is weak. The spectrum of M is red (background slope between ω−1 and ω−2) at subseasonal periods, implying a white or blue spectrum for the external torque on the ocean. Comparisons with previous studies indicate the importance of direct atmospheric forcing in inducing subseasonal M signals, relative to instabilities and other internal sources of rapid oceanic signals. Regional angular momentum estimates show that seasonal variability tends to be larger at low latitudes, but many local maxima exist because of the spatial structure of zonal current and mass variability. At seasonal timescales, latitudes ∼20°S–10°N contribute substantial variability to MΩ, while signals in Mr can be traced to Antarctic Circumpolar Current transports and associated circulation. Variability in M is found to be small when compared with similar time series for the atmosphere and the solid Earth, but ocean signals are significantly coherent with atmosphere-solid Earth residuals, implying a measurable oceanic impact on length-of-day variations.