Lecture 12 Atmosphere circ

Lecture 12 Atmosphere circ - 2/24/09
 GEOL 103 Spring 2009

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Unformatted text preview: 2/24/09
 GEOL 103 Spring 2009 Environment
of
the
Earth
 Lecture 12: Circulation in the atmosphere Radia,ve
warming
of
the
atmosphere
 1.  Solar
radia,on
is
absorbed
by
the
Earth
 2.  Earth’s
surface
warms,
reradiates
energy
as
infrared
radia,on
 3.  Greenhouse
gases
absorb
infrared
radia,on
 4.  Atmosphere
warms
 Suggested Readings: KKC Chapter 4 (on Blackboard) pages 55-65 pages 66-70 Most
of
the
atmosphere
is
compressed
into
the
first
few
km
of
the
troposphere,
so
the
 lowest
por,ons
of
the
atmosphere
are
warmest

 Laws
governing
gases:
 Laws
governing
gases:
 1.  Temperature
increase
results
in
an
increase
in
pressure
(if
there
is
no
change
in
volume)
 • Gas
molecules
collide
with
one
another,
and
against
surfaces
 2.  The
volume
that
a
gas
occupies
will
increase
at
higher
temperatures
 • Collisions
result
in
a
measureable
force
(PRESSURE)
 • Collisions
are
the
result
of
random
kine,c
energy
of
gas
molecules
 • Hea,ng
a
gas
will
result
in
higher
kine,c
energy
of
molecules

more
collisions
 3.  Gas
density
will
decrease
with
increasing
volume
(if
there
is
no
change
in
mass)
 4.  Lower
density
air
will
rise
buoyantly,
un,l
the
air
mass
is
surrounded
by
air
of
equal
density
 5.  Higher
density
air
(cooler
air)
will
sink
 This
behavior
results
in
the
ver,cal
movement
of
air
masses
through
the
atmosphere
 1
 2/24/09
 Air
masses
can
rise
to
the
top
of
the
troposphere,
warm
stratospheric
‘lid’
prevents
 further
ver,cal
mo,on
 Rising
air
mass
will
expand,
water
vapor
will
condense
at
higher
al,tude
 tropopause
 Laws
governing
gases:
 High
 pressure

 Low
 pressure

 L H 1.  Gas
will
always
move
from
a
region
of
high
pressure
to
low
pressure
 2.  Air
masses
follow
pressure
gradients
 Rising
air
mass
 Sinking
air
mass
 Low
 pressure

 H L High
 pressure

 Earth’s
surface
 2
 2/24/09
 Atmospheric
circula,on
 • Air
masses
in
our
atmosphere
move
according
to
the
principles
outlined
here
 • These
principles
explain
why
air
masses
move
 • The
driving
force
behind
atmospheric
circula,on
is
UNEVEN
hea,ng
of
Earths
surface
 The
solar
constant
(S)
is
1370
waZs
per
square
meter
 Earth’s
curved
surface
receives
more
of
this
energy
at
the
equator,
less
at
the
poles
 The
Hadley
circula5on
cell
 Hadley
cell
circula,on
 H Convergence:
Regions
of
low
pressure
where
air
masses
are
flowing
towards
 
 Rain
 L Rain
 H 1.  2.  3.  4.  5.  Upli[
at
equator
 High
rainfall
straddling
equator
 Cool
dry
air
descends
around
30º
 Air
moves
from
high
to
low
pressure‐back
towards
equator
 Called
the
Hadley
cell
 
 
 
example:
equatorial
zone
 Divergence:
Regions
of
high
pressure
where
air
masses
move
away
from
 H 
 
 
 
example:
30
degrees
north
and
south
 The
Hadley
cell
is
a
huge
convec,on
cell
opera,ng
globally
over
60
degrees
 of
la,tude
(6,600
km)
and
12
km
of
al,tude
 Most
notable
over
the
oceans,
somewhat
disrupted
by
con,nents
 3
 2/24/09
 Cool
air
returning
to
the
equator
from
northern
and
southern
hemispheres
 meet
and
rise
once
again
 Zone
of
convergence:
Intertropical
Convergence
Zone
(ITCZ)
 ITCZ
 ITCZ
is
marked
by
high
evapora,on,
heavy
rainfall,
high
cloud
cover
 Equator
 Distribu,on
of
tropical
rainforests
is
controlled
by
loca,on
of
ITCZ
 Rainforest
ecosystems
require
abundant
moisture
 Convec,ve
towers
at
the
ITCZ
 4
 2/24/09
 Circula5on
in
the
mid
to
high
la5tudes
 Cold
temperatures
at
the
poles
create
high
density
air

 Cold
sinking
polar
air
creates
high
pressure
at
the
surface
in
high
la,tudes
 Cold
air
masses
move
away
from
polar
high
pressure
zones,
moving
equatorward
 The
deserts
of
the
world
are
clustered
around
30
degrees
 north
and
south
 Around
60
degrees
north
and
south,
these
cold
air
masses
meet
warm
air
masses
moving
away
 from
the
hadley
cell
 Mee,ng
of
cold
polar
air
and
tropical
warm
air
occurs
in
mid
la,tudes
 The
movement
of
air
is
complicated
by
the
rota,on
on
the
Earth
 5
 2/24/09
 The
Coriolis
effect
 Coriolis
Effect:
 An
apparent
force
that
acts
on
any
object
in
mo,on
on
a
rota,ng
body
 Tendency
for
a
fluid
(air/water)
moving
across
Earth’s
surface
to
be
deflected
from
a
straight
line
 path
 From
above
–
path
of
ball
is
 straight
 The
speed
of
Earth’s
rota,on
varies
with
la,tude
 On
the
carousel
–
path
of
ball
is
 curved
 Fastest
at
equator,
slowest
at
poles
 Deflec,on
of
objects
is
only
apparent
when
viewed
from
the
Earth
 • Deflec,on
is
to
the
right
of
mo,on
in
the
northern
hemisphere
 • Deflec,on
is
to
the
le[
of
mo,on
in
the
southern
hemisphere
 The
outside
of
the
carousel
is
moving
faster
than
the
inside
 Surface
winds
are
a
result
of
convec,on
in
the
troposphere
 and
the
Coriolis
effect
 When
an
air
mass
is
at
the
equator
(point
A),
it
is
moving
from
west
to
east
with
Earth’s
rota,on,
 with
a
velocity
equal
to
the
speed
of
rota,on
at
the
equator
(about
460
meters
per
second)
 The
rate
of
rota,on
is
slower
at
point
B,
so
when
the
air
mass
moves
to
the
north,
it
is
moving
 faster
than
the
ground
below
it
 KKC
figure
4‐11
 The
final
point
of
the
air
mass
is
X,
instead
of
B
which
is
the
straight
line
path
 Add
the
Coriolis
effect
 6
 2/24/09
 Surface
wind
paZerns:
 Northeast
and
southeast
trade
winds:
blow
from
the
east
in
both
hemispheres,
cool
air
 returning
from
the
hadley
cell,
deflected
by
the
Coriolis
force
 mid
la,tude
westerlies:
Air
moving
poleward
deflected
by
the
coriolis
force,
blow
from
the
 west
 Note
that
winds
are
named
for
where
they
appear
to
come
from
 Earth’s
rota,onal
axis
is
,lted
23.5
degrees
from
the
ver,cal
 The
sun
is
directly
overhead
23.5
degrees
north
and
south
on
the
sols,ces
 The
sun
is
directly
overhead
the
equator
on
the
equinoxes
 Land
surfaces
heat
up
and
cool
down
more
rapidly
than
the
oceans
 Zone
of
maximum
surface
hea,ng
varies
through
the
year
 The
ITCZ
is
always
found
in
the
summer
hemisphere
 During
the
day,
rising
air
over
land
creates
low
pressure
and
a
sea
breeze
blows
onto
land
 At
night,
cold
air
over
land
creates
high
pressure
and
a
land
breeze
blows
out
over
the
ocean
 7
 ...
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