Geoscience Reference
In-Depth Information
In the late 1960s, Bjerknes brought together all of these disparate pieces
of information into a hypothesis that seemed to explain the entire ocean-
atmosphere phenomenon. He proposed that, in typical years, the constant
east-to-west (or easterly) trade winds push warm surface waters across the
Pacii c Ocean to the western end, where they pile up in a region called
the “Pacii c warm pool.” h is “pool” of warm water is roughly four times the
size of the continental United States, measuring 9,000 miles from east to
west and 1,500 miles from north to south. High rates of evaporation of this
body of warm water provide abundant rainfall for places such as Australia
and Indonesia.
On the opposite side of the Pacii c, just of the coasts of North and South
America, the surface waters blown to the west by the trade winds are replaced
by colder water from beneath the surface in a process known as “upwelling.”
h ese cold, upwelled waters cool the overlying atmosphere, forming high
pressure, resulting in very dry conditions in the adjacent land areas, including
Ecuador, Peru, and Chile to the south and the American Southwest to the
north.
El Niño Episodes
h is vast, complex ocean-atmosphere system periodically stumbles, however,
when trade winds mysteriously falter or even fail completely for months,
producing the pattern known as El Niño. h is phenomenon, which means
“the child,” was named in South America, where it usually appears around
Christmas and thus the celebration of the birth of the Christ child. During
El Niño, the western Pacii c warm pool—elevated several inches higher than
the eastern Pacii c—is released from the invisible force of the trade winds
that hold it, and it l ows eastward as a low-amplitude—but tremendously
long—wave (called a “Kelvin wave”) across 8,000 miles of the Pacii c Ocean
toward the Americas at about 150 miles per day.
Upon reaching the eastern Pacii c, this wave splits and travels along the
coasts of North and South America, causing sea levels to rise by about six to
ten inches—the amount equal to the height of the wave. Higher sea levels can
lead to coastal l ooding and erosion.
h e wave of warm water also acts as a cap, suppressing the colder,
nutrient-rich waters below. Cold water is denser and thus unable to rise above
the warmer waters. h ese atypically warm surface waters pump water vapor,
heat, and enormous amounts of energy into the atmosphere above, creating
