Geoscience Reference
In-Depth Information
Important points in this chapter
●
Influences on atmospheric circulation
: are in three general classes:
—
Planetary interrelationship
, primarily:
Solar energy input (solar radiation is greater at the equator than the poles)
Seasonal perturbations (latitude of maximum solar radiation changes
with season)
Daily perturbations (the daily cycle in solar radiation changes with season)
—
Persistent perturbations
, primarily:
Ocean versus continent (energy return to the atmosphere differs with
surface)
Continental topography (high relief can interfere with tropospheric flow)
—
Temporary perturbations
, primarily:
Oceanic circulation (temporary fluctuations in SST alter atmospheric flows)
Atmospheric content (changing air content alters atmospheric radiation
transfer)
Land cover (large-scale land-cover change alters surface energy balance)
●
Latitudinal radiation imbalance
: atmospheric and oceanic circulation must
occur to redress the imbalance between the strong latitudinal variation in
incoming solar radiation and the weaker latitudinal variation in outgoing
longwave radiation loss.
Lower atmosphere circulation
—
Latitudinal bands of pressure and wind
: on average, pressure is low at the
equator with southeasterly (northeasterly)
trade winds
north (south) of
the equator; there is high pressure and less wind at 30°N and 30°S, but
stronger westerly winds at 60°N and 60°S.
—
Hadley Circulation
: there is a strong, single summer Hadley cell with
rising air located at the shifting thermal equator with falling air in the
winter hemisphere.
—
Mean low-level circulation
: Coriolis force gives clockwise (counterclock-
wise) circulation around high (low) pressure in the northern hemisphere
most noticeable over oceans around high pressure at 30°N and 30°S. The
circulation is reversed in the southern hemisphere. There is a seasonal
shift in the circulation pattern as the thermal equator moves north-south
that is different between hemispheres because the northern hemisphere
has a larger land area.
—
Mean upper-level circulation
: at
●
10 km atmospheric circulation intensi-
fies with strong westerly winds in both hemispheres in the subtropics and
middle latitudes where the tropospheric
jet streams
continually develop,
meander and decay giving less consistent lower-level winds and hydro-
meteorological variability.
∼
Ocean circulation
—
Thermal structure
: oceans have a (
●
100-1000 m deep)
mixed layer
separated from the deep ocean by the
thermocline
, a steep negative
temperature gradient.
∼
