Independent Components in the Northern Hemisphere Winter: Is the Arctic Oscillation Independent?
Independent Components in the Northern Hemisphere Winter: Is the Arctic Oscillation Independent?
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DOI：
10.2151/jmsj.85.825
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发表时间：
2007-12
影响因子：
3.1
通讯作者：
Hisanori Itoh;A. Mori;S. Yukimoto
中科院分区：
文献类型：
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作者：
Hisanori Itoh;A. Mori;S. Yukimoto
本文用独立分量分析（伊卡）研究了北方冬季大气的真实振荡。伊卡在假设真实振荡相互独立的前提下，可以区分真实振荡和视在振荡。特别注意北极涛动（AO）。为此，使用NCEP-NCAR再分析资料（NCEP-NCAR资料）和气象研究所的现代气候试验资料（MRI资料）。伊卡在气象学中的应用可能存在一些问题：数据周期的选择、噪声的处理以及相空间维数与独立分量数之间的关系。我们就这些问题提出几点思考和建议。伊卡应在方差几乎相同的期间进行。由于白化后的独立分量在噪声的存在下不一定相互不相关，并且相空间的维数与独立分量的数量之间的关系不能预先确定，因此我们提出了在气象学中最相关的峰度寻求独立分量的方法。基于上述考虑和建议，对NCEP-NCAR数据进行了伊卡。海平面气压（SLP）和500 hPa高度场（Z500）的独立分量。它们是北大西洋涛动（NAO）和太平洋-北美涛动（PNA）。因此，AO是从它们导出的表观模式。然而，由于数据周期太短，无法获得统计学显著性。然后，对MRI数据执行伊卡。同样在这个数据中，NAO和PNA样振荡对于SLP和Z500都是独立的，其中PNA样振荡意味着它的模式与观察到的PNA模式有些不同。可以再次得出结论，AO不是独立的，但这次具有统计学意义。
This paper examines true oscillations in the Northern Hemisphere winter by using independent component analysis (ICA). ICA can distinguish between true and apparent oscillations under the assumption that the true oscillations are mutually independent. Particular attention is paid to the Arctic Oscillation (AO). For this purpose, the NCEP-NCAR reanalysis data (NCEP-NCAR data) and the data of the present climate experiment of the Meteorological Research Institute (MRI data) are used. There may be certain issues in ICA applied to meteorology: the selection of data periods, treatment of noise, and relationship between the number of dimensions in phase space and the number of independent components. We make several considerations and proposals about these issues. ICA should be performed for periods for which the variance is almost the same. Since independent components after whitening are not necessarily uncorrelated with each other under the existence of noise, and the relation between the dimension of phase space and the number of independent components cannot be predetermined, we propose the method for seeking independent components by kurtosis as the most relevant in meteorology. On the basis of the above considerations and proposals, ICA is performed on the NCEP-NCAR data. Independent components are found for the sea level pressure (SLP) and 500 hPa height (Z500) fields. They are the North Atlantic Oscillation (NAO) and the Pacific-North American Oscillation (PNA). Thus, the AO is an apparent mode derived from them. However, since the period of the data is too short, statistical significance cannot be obtained. Then, ICA is performed on the MRI data. Also in this data, the NAO and the PNA-like oscillation are independent for both the SLP and Z500, where the PNA-like oscillation implies that its pattern is somewhat different from the observed PNA pattern. It can be concluded again that the AO is not independent, but this time with statistical significance.