Section 8.3.4.4 Northern Hemisphere Winter Teleconnections

Northern Hemisphere winter teleconnections

Explanation of the derivation of the teleconnection climagrams available on Opencharts.

A variety of statistical methods have been used in the literature to define Northern-Hemisphere (NH) teleconnection patterns.  Here, leading variability patterns for the NH winter are defined by an EOF analysis of re-analysis monthly-mean geopotential height at 500 hPa for the December-to-March season, in the 30-year period (1981-2010). The analysis has been applied to three sectors in the latitude belt 25-85 N: the Pacific/North American sector (160E-80W), the Atlantic/European sector (80W-40E), the Asian/Pacific sector (40E-160E)

Fig8.3.4.4-1: Northern Hemisphere winter teleconnections

The analysis has been applied to three sectors in the latitude belt 25-85 N: the Pacific/North American sector (160E-80W), the Atlantic/European sector (80W-40E), the Asian/Pacific sector (40E-160E). Data are from the ERA-Interim re-analysis until winter 2009/10, from operational ECMWF analyses afterwards.  The first EOF defined in each of the three sectors corresponds to a well-documented teleconnection pattern: respectively, the Pacific/North American pattern, the North Atlantic Oscillation, and the Eurasian pattern.  These patterns are shown in the top row of the above figure, the portion within the grey sector boundary corresponds to the regionally-normalized EOF (for continuity, regressions of height anomalies onto the corresponding PC are shown over the whole hemisphere).  The positive phase of these patterns correspond to an intensification of the westerly winds over the central and eastern parts of the North Pacific and North Atlantic, and over central and eastern Siberia respectively.  The second EOF of the Pacific/North American and the Atlantic/European sector are also retained, since they modulate the intensity and position of the stationary-wave ridges over the north-eastern parts of the Pacific and Atlantic oceans.  The sign convention for these EOFs (referred to as the North Pacific dipole and the East Atlantic pattern) is such that positive projections correspond to an amplification of the respective stationary-wave ridge.