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Teleconnection Indices
JANUARY 2020
FIGURE E7.
Standardized
monthly Northern Hemisphere teleconnection indices. The teleconnection
patterns are calculated from a Rotated Principal Component Analysis (RPCA)
applied to monthly standardized 500-hPa height anomalies during
1950-2000. To obtain these patterns, ten leading
un-rotated modes are first calculated for each calendar month by using
the monthly height anomaly fields for the three-month period centered
on that month: [i.e., The July modes are calculated from the June,
July, and August standardized monthly anomalies]. A Varimax spatial
rotation of the ten leading un-rotated modes for each calendar month
results in 120 rotated modes (12 months x 10 modes per month) that
yield ten primary teleconnection patterns.The teleconnection indices
are calculated by first projecting the standardized monthly anomalies
onto the teleconnection patterns corresponding to that month (eight or
nine teleconnection patterns are seen in each calendar month). The
indices are then solved for simultaneously using a Least-Squares
approach. In this approach, the indices are the solution to the
Least-Squares system of equations which explains the maximum spatial
structure of the observed height anomaly field during the month. The
indices are then standardized using the 1981-2010 base period means for each pattern and calendar month
independently. No index value exists when the teleconnection pattern
does not appear as one of the ten leading rotated EOF's valid for
that month.
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