Summer sea surface temperature variability off Vancouver Island from satellite data

Satellite‐sensed advanced very high resolution radiometer (AVHRR) sea surface temperature (SST) data over eight summers (1984–1991) were used to analyze the summer SST patterns of variability off the west coast of Vancouver Island. Empirical orthogonal function (EOF) analysis of the spatial variance for 133 nearly cloud‐free summer images was performed. The first EOF mode, which resembled the mean of all images, showed a strong cool water band located at the northwest corner of Vancouver Island, a cool tongue extending seaward from the Strait of Juan de Fuca and a warm patch off Barkley Sound. The second mode revealed topographically controlled upwelling: cool water over the shelf region with its seaward boundary roughly following the 200‐m depth contour, plus a cold eddy located just north of the Juan de Fuca Canyon. The third mode displayed cool water extending southwestward off Brooks Peninsula, while the fourth mode showed a cool water plume extending off Cape Scott at the northern tip of Vancouver Island. These four modes accounted for 33, 12, 10, and 5% of the SST variance, respectively. The temporal amplitude of these EOF modes revealed how the SST features changed as summer progressed. From these images, we also constructed an overall seasonal coolness index, which revealed the summers of 1986 and 1991 to have the coolest coastal water, with both summers immediately preceding an El Niño.