Geoscience Reference
In-Depth Information
25
10
0
Tropopause
10
10
-60
Isovels m s
-1
20
20
20
10
-60
Isothermals
o
C
-40
-40
30
-80
15
20
jet stream
core
The zonal winds are the
strongest component of the
global circulation: you
should imagine the winds
flowing normal to and out
of the plane of section
represented by the page
-60
jet stream
core
-40
10
5
0
0
0
westerlies
westerlies
trades
trades
90
o
S
60
o
S
30
o
S
0
o
30
o
N
60
o
N
90
o
N
Easterlies
Easterlies
Zonal here refers to wind flow normal to a circumferential section from North pole to South pole, showing the strongest
East-West components of the global circulation.
Fig. 6.7
Mean zonal winds and temperatures in January; zonal here refers to wind flow normal to a circumferential section from North pole to
South pole.
Notes
:
1
Jet stream with mean speeds of 30-40 ms
1
at limits to tropopause in regions of strong temperature/pressure gradients.
2
Discontinuities in level of troposphere at midlatitudes due to low-latitude convective upwelling and high-latitude convective sinking.
3
Greater upper troposphere wind strength in northern hemisphere winter due to enhanced seasonal contrast between the cooling northern
hemisphere and equatorial regions.
4
Little variation of
T
with latitude in the tropical zone (
barotropic
condition), gradients increasingly diverging poleward (
baroclinic condition
)
5
Very high velocities of near-surface southern hemisphere high-latitude winds (not shown here, see Fig. 6.4) due to high-pressure gradients
there.
N
tion of water vapor to rain or cloud droplets and the air
heats up. The large volumes of atmosphere involved mean
that the process is very important in atmosphere-ocean
coupling (Section 6.2).
2
Sensible heat energy
,
E
S
, arises from the direct impact
of radiation, the atmosphere losing or gaining sensible
heat by radiation to and from space and from clouds. It is
given by the product of the specific heat capacity at con-
stant pressure,
c
p
(J kg
1
K
1
), and temperature,
T
(K).
Water has a very high specific heat capacity (around
4,000 J kg
1
K
1
) compared to that of air (around
1,000 J kg
1
K
1
).
3
Potential energy
,
E
P
, is that of position,
y
, above sea
level, times gravity.
The total energy,
E
, present in any imaginary unit mass
of moist air must remain constant; thus
E
Fig. 6.8
Simple Hadley circulation on a nonrotating Earth.
water vapor (Section 3.4). It is given by the product of the
latent heat of evaporation or condensation (
L
, 2.3
10
5
J kg
1
)
times the mass (
m
) of water vapor involved. Evaporation
of water into a parcel of air requires work to be done
breaking hydrogen bonds and hence energy is taken in
(from the other energy sources in the atmosphere) and
cooling takes place. The opposite holds during condensa-
E
L
E
S
E
P
constant. This
conservation of energy
equation allows us to understand
energy changes in ascending or descending air masses.
Such motions dominate heat exchange in the tropics and
constant or
E
Lm
c
P
T
yg
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