PDO = Pacific Decadal Oscillation a North Pacific phenomenon (probably linked somehow to ENSO) involving ocean-atmosphere interactions, with consequences mainly for North America; return time about 50 years
AO = Arctic Oscillation
a purely atmospheric phenomenon with primary influence in high latitudes.
Varies on timescales from days to decades.
http://tao.atmos.washington.edu/analyses0500/ Go to parts IIb, IIIb, and IVb for the maps shown in class.
El Nino events have been happening for thousands of years, and were noted by fishermen in Peru at least as early as the 16th century. It has global impacts. El Nino events commonly bring heavy rain and poor fishing to the tropical west coast of South America, droughts and fires to northern Australia and Indonesia, heavy rains to southern California, and above-normal temperatures in northwestern North America and Japan.
PDO and ENSO have comparable influence on Northwest climate, with warm phases bringing somewhat warmer, drier winter and spring climate, and cool phases bringing somewhat wetter (and ever so slightly cooler) winter and spring climate.
Owing to their combined influence on temperature and precipitation, they have relatively large influences on snowpack and spring streamflow in the Northwest.
PDO has a see-saw influence on salmon abundance: warm phases tend to see increased salmon abundance in Alaska and decreased abundance in Washington, Oregon, and California.
In the Northwest, warm phase PDO, with reduced snowpack, favors
high-elevation tree growth and suppresses low- and moderate-elevation tree
growth.