This index is the cumulative summation of negative northwesterly atmospheric circulation frequency anomalies: Z (westerly), M1, (northwesterly), and M2 (southwesterly) for December through March. An increasing trend in Pacific Circulation Index (PCI) reflects increased westerly and southwesterly atmospheric circulation off the west coast of Canada.
Correct citation: J. R. King, V. V. Ivanov, V. Kurashov, R. J. Beamish, G. A. McFarlane. General circulation of the atmosphere over the North Pacific and its relationship to the Aleutian Low. (NPAFC Doc. No. 318). 18 p. Dept. of Fisheries and Oceans, Sciences Branch - Pacific Region, Pacific Biological Station, Nanaimo, BC, Canada, V9R 5K6. Arctic and Antarctic Research Institute, 38 Bering Street, St. Petersburg, Russia, 199397.
Full document: https://waves-vagues.dfo-mpo.gc.ca/Library/40961357.pdf