Geoscience Reference
In-Depth Information
—
Sea-surface temperature (SST)
: isotherms run roughly east-west from
∼
29°C at the equator to -2°C near the poles, but are modified near conti-
nents by wind-driven surface currents carrying warm water toward
(cooler water from) the poles on the eastern (western) side of
continents.
—
Thermohaline circulation
: originates near the poles (from increased
salinity due to sea water freezing) as vertical flow that becomes horizontal
in the middle/lower ocean, with compensating upward branches widely
spread across the globe: it is very slow (
∼
1000s years) but has decadal
changes that influence climate.
Oceanic influences on continental hydroclimate
—
Monsoon flow
: difference in near-surface air temperature in winter gives
flow of dry, cool air from a colder continent to a warmer nearby ocean,
but in summer warm, moist air flow from ocean to warmer land where
ascent gives heavy precipitation.
—
Tropical c yclones
: originate over ocean that has SST
●
26-27°C and is at
least 5-8° north and south of the equator and generally move westward
and toward the poles giving a major detrimental impact if they reach
land.
—
El Niño-Southern Oscillation (ENSO)
: Pacific trade winds support easterly
equatorial flow and warmed waters form an eastern Pacific warm pool
above which there is convection, with ascent in part supported by
enhancing the trade winds. From time to time there is relative warming
of the normally cooler SST in the eastern Pacific (El Niño) with greater
atmospheric convection locally. The resulting advection moderates the
strength of the trade winds, hence there is more warm water farther east
and El Niño tends to be self-supporting for a period of 6 to 18 months.
The shift in the center of convection has consequences on climate globally.
The opposite phenomenon when the SST in the eastern Pacific is colder
than average is La Niña.
—
Pacific Decadal Oscillation (PDO)
: a long-lived El Niño-like pattern of
Pacific climate variability that persists for 20-30 years and which has
most impact in the North Pacific and North America.
—
North Atlantic Oscillation (NAO)
: a variation in the strength and position
of the
Icelandic Low
and the
Azores High
which control the direction and
strength of westerly winds in the Atlantic which in turn modify the
seasonal climate of Western Europe.
>
References
Peixoto J.P. & Oort, A.H. (1992)
Physics of Climate.
Springer-Verlag, New York.
Picard, G.L. & Emery, W.J. (1982)
Descriptive Physical Oceanography
, 4th edn. Pergamon
Press, New York.
Rassmusson, E.M., Dickinson, R.E., Kutzbach, J.E. & Cleaveland, M.K. (1993) Climatology.
In:
Handbook of Hydrology
(ed. D. Maidment) pp. 2.1-3.1. McGraw-Hill, New York.
