Pacific–South American 1

PC2 of monthly Z500 anomalies south of 20°S (EOF1 is the SAM), projected daily. Positive = ridge over the Amundsen–Bellingshausen Seas (El Niño-like). EOF2/EOF3 form a near-degenerate pair, so PSA1/PSA2 can mix; sign conventions vary. — Mo & Higgins 1998, Mon. Wea. Rev. 126, 1581–1596; Mo & Paegle 2001, Int. J. Climatol. 21, 1211–1229, doi:10.1002/joc.685