Download Thermal Circulations PGF

Thermal Circulations
warm air
atmospheric
columns of air
cold air
PGF
PA
PB
Psurf=1000mb
Psurf=1000mb
Since Pressure ∝ mass above:
at level Z, PB > PA
ALOFT, get PGF towards the cold air column
height = Z
THERMAL CIRCULATION
L
H
H
L
surface
COLD
WARM
WINTER
Clear skies and winds blow
from land to sea
SUMMER
Warm humid air blows up from
equator bringing rainy weather.
Clicker Question
Set Frequency to "BB"
We know that the Earth is warmer at the equator and colder
at the poles. Assume for the moment, there is no Coriolis force.
Which way would you expect the surface wind to blow at X?
A
(A) Southerly (poleward)
X
D
B
(B) Westerly
Equator
C
(C) Northerly (equatorward)
(D) Easterly
Clicker Question
Set Frequency to "BB"
We know that the Earth is warmer at the equator and colder
at the poles. Assume for the moment, there is no Coriolis force.
Which way would you expect the surface wind to blow at X?
A
(A) Southerly (poleward)
X
D
B
(B) Westerly
Equator
C
(C) Northerly (equatorward)
(D) Easterly
Single Cell Model
Originally proposed by G. Hadley
"Hadley Cell"
- warm air at equator rises
- goes poleward at higher levels
- sinks at poles
- moves equatorward at the surface A (Very Large) Thermal Circulation
HOWEVER,
Due to the Earth's rotation, the single cell model is
too simplified and would result in extremely strong
winds due to Coriolis force and become unstable.
A more realistic view of the global circulation is
provided by the "3-Cell Model"
- Certainly not perfect, but does explain many
features of the global circulation system
NP
EQ
SP
3-Cell Model
- no land mass
- time averaged
- no seasons
NP
60
30
Hadley Cell
EQ
SP
NP
Ferrel Cell
60
30
Hadley Cell
EQ
SP
Polar Cell
NP
Ferrel Cell
60
30
Hadley Cell
EQ
SP
Polar Cell
SURFACE
WINDS
NP
Ferrel Cell
60
30
Hadley Cell
EQ
SP
Polar Cell
SURFACE
WINDS
NP
Ferrel Cell
60
30
Hadley Cell
EQ
SP
Polar Cell
SURFACE
WINDS
NP
Ferrel Cell
60
30
Hadley Cell
EQ
SP
Polar Cell
NP
Ferrel Cell
60
30
Hadley Cell
EQ
TRADEWINDS
-Northeasterly in NH
SP
Polar Cell
NP
Westerlies
Ferrel Cell
60
- 30-60 Mid-latitudes
30
Hadley Cell
EQ
SP
Polar Cell
Polar
Easterlies
NP
Ferrel Cell
60
30
Hadley Cell
EQ
SP
Similar System of Cells
in Southern Hemisphere
Polar Cell
NP
Ferrel Cell
60
30
Hadley Cell
EQ
Hadley Cell
30
Ferrel Cell
60
SP
Polar Cell
Surface LOWS where
air is RISING
60
L
Polar Cell
NP
L
RISING AIR
Ferrel Cell
L
30
Hadley Cell
L
L
EQ
L
RISING AIR
Hadley Cell
30
60
L
L
Ferrel Cell
L
RISING AIR
SP
Polar Cell
SINKING AIR
Surface HIGHS where
air is SINKING
NP
H
L
60
Polar Cell
L
Ferrel Cell
L
SINKING AIR
H
30
H
H
Hadley Cell
L
L
EQ
L
Hadley Cell
H
30
H
H
SINKING AIR
60
L
L
Ferrel Cell
L
H
SINKING AIR
SP
Polar Cell
Clicker Question
Set Frequency to "BB"
In general, what sort of surface conditions would you expect at about 30° where the Hadley cell meets the Ferrell cell?
(A) stormy, cool and moist with much precipitation
(B) few storms, warm and dry with little precipitation
Clicker Question
Set Frequency to "BB"
In general, what sort of surface conditions would you expect at about 30° where the Hadley cell meets the Ferrell cell?
(A) stormy, cool and moist with much precipitation
(B) few storms, warm and dry with little precipitation
Desert Regions
Desert Regions
30°˜N
30°˜S
ITCZ
Intertropical Convergence
Zone (ITCZ): Region of
NP
Cumulus Towers and
H
Precipitation
60
L
L
H
30
Polar Cell
Ferrel Cell
L
H
H
Hadley Cell
ITCZ
L
L
EQ
L
Hadley Cell
H
30
60
H
L
L
H
Ferrel Cell
L
H
SP
Polar Cell
ITCZ
ITCZ
Polar Front: Where
Westerlies meet Polar
Easterlies
L
60
Polar Front
H
30
Polar Cell
NP
H
L
Ferrel Cell
L
H
H
Hadley Cell
ITCZ
L
L
EQ
L
Hadley Cell
H
30
H
H
Polar Front
60
L
L
Ferrel Cell
L
H
SP
Polar Cell
Idealized Water Planet
Real Earth
Average Pressure Patterns in July
Average Pressure Patterns in January
Semi-permanent Subtropical Highs
Pacific High
- Pacific High is an important factor
for California's climate
Bermuda High