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Spatial Patterns and Trends of Summertime Low Cloudiness for the Pacific Northwest, 1996–2017
Author(s) -
Dye Alex W.,
Rastogi Bharat,
Clemesha Rachel E. S.,
Kim John B.,
Samelson Roger M.,
Still Christopher J.,
Williams A. Park
Publication year - 2020
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2020gl088121
Subject(s) - empirical orthogonal functions , cloud cover , climatology , environmental science , pacific ocean , geography , oceanography , geology , cloud computing , computer science , operating system
Abstract Summertime low clouds are common in the Pacific Northwest (PNW), but spatiotemporal patterns have not been characterized. We show the first maps of low cloudiness for the western PNW and North Pacific Ocean using a 22‐year satellite‐derived record of monthly mean low cloudiness frequency for May through September and supplemented by airport cloud base height observations. Domain‐wide cloudiness peaks in midsummer and is strongest over the Pacific. Empirical orthogonal function (EOF) analysis identified four distinct PNW spatiotemporal modes: oceanic, terrestrial highlands, coastal, and northern coastal. There is a statistically significant trend over the 22‐year record toward reduced low cloudiness in the terrestrial highlands mode, with strongest declines in May and June; however, this decline is not matched in the corresponding airport records. The coastal mode is partly constrained from moving inland by topographic relief and migrates southward in late summer, retaining higher late‐season low cloud frequency than the other areas.