Sunday, April 26, 2009

The Atlantic Multidecadal Oscillation - Part II

This post concerns a separation of the linear and non-linear components of the Atlantic Multidecadal Oscillation (AMO) from 1982 to 2007 using the Earth Trends Modeler.

The first step in creating this separation was to remove the effects of other climate teleconnections. In an analysis of sea surface temperature teleconnections using the Empirical Orthogonal Teleconnection procedure in the Earth Trends Modeler (see the previous post), the AMO was the second EOT. Thus to remove the effects of other teleconnections, the Linear Modeling tool in the Earth Trends Modeler was used to create a residual series after removing the effects of EOT's 1 and 3-10.

The next step was to run a linear model using this residual series as the dependent variable and two unidimensional time series -- one being a simple linear series (the Earth Trends Modeler has a simple utility to create this) and a second being a detrended version of EOT2. The graphs below show the AMO as measured by EOT2 along with the detrended AMO.

The two images showing the linear and non-linear components of the AMO at the top of this post are the Partial Correlation images of the linear series and the detrended EOT2.

Many areas of the North Atlantic basin show a strong relationship with both the linear and non-linear components. Both images show a strong relationship with the North Atlantic Subpolar Gyre (the dark red area in the Labrador Sea However, there is one striking difference -- the non-linear pattern shows a structure consistent with the negative phase of the North Atlantic Oscillation (NAO) (click here for the graphic). In fact, using a 7-month mean filter on both the NAO index and the non-linear component of the AMO shows that they are negatively correlated (r = -0.46):

Latif et al. (2007) (Latif, M., C. W. Böning, J. Willebrand, A. Biastoch, F. Alvarez, N. Keenlyside, and H. Pohlmann, 2007: Decadal to multidecadal variability of the Atlantic MOC: Mechanisms and Predictability, in Schmittner, A. J. C. H. Chiang, S. R. Hemming (Eds.) : Ocean Circulation: Mechanisms and Impacts - Past and Future Changes of Meridional Overturning, AGU Monograph 173, American Geophysical Union, 149 -166.) provide evidence of a relationship between low-frequency variability of the NAO and the Atlantic meridional overturning circulation (MOC) with which the AMO is thought to be associated. However, this analysis suggests that an even higher frequency relationship may exist.

1 comment:

  1. Great applications here! From the recent Idrisi Taiga literature, it appears that the seasonal trends analysis module, the PCA module, and maybe others have true three-dimensional analysis capabilities. Is this actual 3-D (voxel) analysis using 3-D coordinates, or "2.5"-dimensional analysis using the same coordinates in serial? If it is true 3-D analysis, is it possible to apply these modeuls to other datasets - for example, the three-dimensional distribution of artifacts at an archaeological site?