Download GLOBAL ATMOSPHERIC CIRCULATION I. Global air pressure and

GLOBAL ATMOSPHERIC CIRCULATION
I.
Global air pressure and winds
A.
4 factors shaping patterns
1.
Heat imbalance
2.
Migration of sun’s perpendicular rays
3.
Coriolis force - the rotation of the Earth deflects winds to the right in the Northern
Hemisphere and to the left in the Southern Hemisphere
4.
Distribution of land and water
B.
The 3-cell model of generalized global atmospheric circulation
1.
Components
a.
Hadley cells
b.
Ferrell cells
c.
Polar cells
d.
ITCZ-Intertropical convergence zone
(1)
Band of low pressure and instability at equator due to intense surface
heating and wind convergence (tradewinds)
(2)
Migrates north and south of Equator over a year, as do all seven of these
components
e.
Polar High
(1)
Dry descending air
(2)
Driest places on Earth
(3)
Polar high is broken into two highs because of large NA landmass
(a)
Canadian high
i)
Source of US cold air
(b)
Siberian high
f.
Subtropical Highs (30 N and S)
(1)
Descending air warms and stabilizes atm
(2)
Major deserts found at these latitudes
(3)
Shift north and south over year
(4)
Well-developed over oceans
(a)
Oceanic high pressure is asymmetric.
i)
East side-stable
ii)
West side-unstable
(5)
Atlantic STHP (aka the Bermuda High)
g.
Tradewinds
(1)
Blow east to west
(2)
Descending air from subtropical high blows toward ITCZ
(3)
Hawaii is in the trade winds
h.
Westerlies
(1)
Blow west to east
(2)
Descending air from subtropical high blows west to east
(3)
Weather patterns in US travel west to east
i.
Polar Easterlies
(1)
Cold, dry winds from Polar high
(2)
Flow away from poles and collide with Westerlies
j.
Polar front
(1)
Marks a shifting zone of instability
(2)
Convergence of Polar Easterlies and Westerlies
(3)
Location of the polar jet stream
(a)
Tropospheric high-velocity wind current
(4)
Deviations in the flow of the polar jet stream
(a)
Azonal flow
i)
N-S waves in jet stream form
ii)
Maximum heat transfer
iii)
Waves form high and low pressure systems
(b)
Zonal flow
(5)
(6)
(7)
C.
i)
E-W flow--no waves
ii)
Minimal heat transfer
Mid-latitude cyclones common
(a)
Large low pressure system that form and travel from west to east
along polar jet stream
(b)
Comprised of warm fronts and cold fronts
(c)
These systems mix warm and cold air
(d)
Transient low pressure system. They typically last 7 to 10 days as
they travel along the polar front
Shifts in the position of the jet stream cause our weather to change
Average position of the polar jet shifts to the north in the summer
Keep in mind thatall of these circulation features shift back and forth, north and south,
throughout the year, in response to the Earth’s orbit around the sun.