|
OCEAN CURRENTS
The ocean water off of the
West Coast are typically cold during much of the year. The underlying reason
for this can be explained by understanding the basics of ocean currents, especially
in the Pacific Ocean.
The major ocean currents
can be determined by the major atmospheric wind systems over the oceanic basins.
Despite slight changes from season to season, the Pacific Ocean is dominated
by a subtropical high pressure region. The wind circulation around an area of
high pressure is clockwise in the Northern Hemisphere. This constant wind pattern
directs the ocean currents also in a clockwise flow around the oceanic basin.
In other words, the main Pacific ocean currents flow from the equator northward
along the coast of Asia, east to the Gulf of Alaska, and southward along the
coast of North America.
Both ocean and wind currents
help keep a constant a global balance of temperature. For example, the northbound
ocean current off the coast of Japan, known as the Kuroshio current, is a warm
current that brings equatorial water to the North Pacific. Likewise the southbound
current off the West Coast, known as the California current, is a cold current
that carries polar water to the waters off of Central America.
Therefore, the cold California
ocean current is responsible for keeping the coastal waters of the West coast
typically cold. Frequently in the summer, the immediate coastal waters turn
even colder especially during periods of steady northwest winds. This can be
explained by understanding the basics of upwelling.
The wind pattern drives
the ocean currents in the near surface water. But at ocean depths of 100 to
200 feet, the current behaves differently. Friction and other forces cause to
deeper ocean water to move slower and turn to the right of the main surface
current. This is known as the Ekman drift. Let's put this idea into perspective.
Typically, the predominant summer wind direction along the coast is from the
northwest. This enhances the southbound surface ocean current in the coastal
waters. In the subsurface ocean waters, the southbound current is slowed and
deflected to the right or toward the west. The subsurface water is pulled away
from the coastline. To fill the void, water from the ocean bottom is pulled
toward the surface; this process is called upwelling. The water which rises
from deeper levels is colder than the water it replaces. This leads to colder
ocean temperatures in regions of upwelling.
Upwelling is a common occurrence in the coastal waters during the summer. It
also has a significant impact on the area's cool coastal summertime climate.
|
www.weather.gov 
