Daily amplitudes of the Arctic Oscillation (AO) the North Atlantic Oscillation
(NAO), and the Pacific-North American (PNA) pattern (top left panel). The pattern
amplitudes for the AO, (NAO, PNA) are calculated by projecting the daily 1000-hPa
(500-hPa) height anomaly field onto the leading EOF obtained from standardized
time-series of daily 1000-hPa (500-hPa) height for all months of the year. The base
period is 1979-2000. Northern Hemisphere mean and anomalous 500-hPa geopotential height
(CDAS/Reanalysis) for selected periods during the month are shown in the remaining 3
panels. Mean heights are denoted by solid contours drawn at an interval of 8 dam.
Anomalies are calculated as departures from the 1981-2010 base period daily means.