This index measures the relative intensity of the Aleutian Low pressure system of the north Pacific (December through March). It is calculated as the mean area (km²) with sea level pressure <= 100.5 kPa and expressed as an anomaly from the 1950-1997 mean. A positive index value reflects a relatively strong or intense Aleutian Low. The index was completely regenerated using a new method in 2015. The new method produces Aleutian Low Pressure Index (ALPI) values that are comparable to previously published values (1900-2008), and there is no difference in the periods with positive or negative values. To make use of this index, you are requested to cite the manuscript (below).
Correct citation: Surry, A.M., and King, J.R. 2015. A new method for calculating ALPI: The Aleutian Low Pressure Index. Can. Tech. Rep. Fish. Aquat. Sci. 3135: v + 31 p.
Full document: http://waves-vagues.dfo-mpo.gc.ca/Library/359380.pdf