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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

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within the latitude belt

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25N-

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85N:

1. the Pacific/North American sector (160E-80W)

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1. .
2. the Atlantic/European sector (80W-40E)

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1. .
2. the Asian/Pacific sector (40E-160E)

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1. .

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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.

Data are from the ERA-Interim re-analysis until winter 2009/10, from operational ECMWF analyses

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thereafter.  

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Fig8.3.4.4-1: Northern Hemisphere winter teleconnections

EOF No1 is defined in each of the three sectors and corresponds to a well-documented teleconnection pattern:

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1. the Pacific/North American pattern

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1. .
2. the North Atlantic Oscillation

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1. .
2. the Eurasian pattern.

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The positive phase of these patterns

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corresponds to an intensification of the westerly winds over

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:

1. central and eastern parts of the North Pacific.
2. central and eastern parts of the North Atlantic

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1. .
2. over central and eastern Siberia

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1. .

These patterns are shown in the top row of Fig8.3.4.4-1.  

EOF No2 of the Pacific/North American and the Atlantic/European sector are also retained

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. This is because they modulate the intensity and position of the stationary-wave ridges over:

1. the north-eastern parts of the Pacific

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1. Ocean.
2. the north-eastern parts of the Atlantic Ocean.

The positive EOFs correspond to an amplification of stationary-wave ridge pattern.  These are referred to as:

1. the North Pacific dipole

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1. .
2. the East Atlantic pattern

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These patterns are shown in the bottom row of Fig8.3.4.4-1.