The North Pacific Gyre Oscillation (NPGO) is the oceanic expression of the atmospheric North Pacific Oscillation (NPO), which features seesawing surface air pressures between high (55-65°N) and middle (30-40°N) latitudes in the northeastern Pacific Ocean. Variations in the NPO also generate Rossby waves in the ocean which affect the Kuroshio and its eastward extension, meaning that the North Pacific Oscillation has a large effect on the surface circulation of the entire North Pacific Ocean.
When the NPO is in its positive phase, the air pressure differential between higher land lower latitudes is enhanced, leading to stronger northerly winds and a stronger North Pacific Gyre. When the NPO is in its negative phase, the opposite occurs: the pressure differential is smaller, southerly winds gain strength, and the gyre slows down. This fluctuation in North Pacific Gyre strength affects upwelling and biological markers such as chlorophyll counts throughout the northeastern Pacific.
The connection to the Kuroshio off of Japan and its eastern
extension has a 2-3 year lag, due to the time required for the Rossby wave to
propagate westward. Many responses of the ocean are significantly behind
atmospheric forcing, due to the much greater density (~800x) of ocean water
relative to air. The transfer of momentum is far slower through the ocean than
through the air.
Tomorrow: Ekman transport.
Be brave, and be well.
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