MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
MAR 110 LECTURE #9
Earth’s Heat Budget / Atmosphere Dynamics
External Energy Source-the Sun
The portion of the sun’s energy that is intercepted by the Earth powers
most of the Earth’s environmental processes. (UWaC)
The Earth’s Overall Heat Budget
–HEAT IN = HEAT OUT
The Earth’s globally-averaged temperature, that is also
averaged over the year, is virtually constant. This is so because
the total amount of infrared energy radiated away from the Earth
(short arrows around the globe) equals the total amount of solar
energy absorbed by the Earth. (UWaC)
1
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
“Short Wave” Solar Energy
Different types of energy in the universe is transported by waves with
spectrum of wavelengths; stretching from gamma rays with extremely small
wavelengths (i.e., a millionth of a micrometer –the size of an atom) to radio
waves with very large wavelengths (i.e., 100 million micrometers – the size of
a tall building). The temperature of the source of radiation determines the
o
wavelength of the radiation. For example, the 6000 K sun produces visible
“short wave” solar radiation. (UWaC)
2
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Temperature – A Digression
(LEFT) Temperature is molecules in motion. (RIGHT, left) The Kelvin
temperature scale measures absolute temperature ranging upward
0
from the coldest possible temperature (at 0 K all molecular motion
stops!). (middle) The Celsius temperature scale is more convenient in
o
that it is referenced to the melting point temperature of ice at 0 C and
o
o
o
boiling water at 100 C. NOTE: 0 C = 273.16 K. (right) The Fahrenheit
temperature scale is referenced to the ice melting point, which is at
o
o
o
o
o
32 F = 0 C ( = 273.16 K) and boiling water at 212 F= 100 C. (ItO??)
“Long Wave” Infrared Energy
o
The Earth with its relatively lower temperature of ~290 K, produces relatively
uniform “long wave” infrared radiation (invisible) over it’s entire surface (see
Figure 13.2) This uniformity results because the variations of the absolute
temperature over the Earth’s surface are so small. (UWaC)
3
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Solar Heat Flux Varies with Latitude
Equal amounts of incoming solar energy (represented by the black
bands) are spread over larger areas of the Earth at polar latitudes and
smaller areas at equatorial latitudes; as illustrated by the flashlights to
the left. The heat energy per unit area - called heat flux- associated
with solar radiation is thus larger in equatorial regions than in polar
regions. It follows that the larger the heat flux the larger the warming.
(UWaC)
4
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Non-Uniform Energy Distributions
The annual average of outgoing infrared radiation heat
flux is uniform, while the corresponding incoming solar
radiation heat flux varies in respect to latitude. Thus
there is an annual net gain of heat due to radiation in
the tropical latitudes and a corresponding net loss of
heat in the polar latitudes. This geographical heat
imbalance is what drives the combined atmospheric
and oceanic circulation; which eliminates the heat
imbalance by transporting the surplus tropical heat to
the heat-starved polar regions. (UWaC)
Atmospheric & Oceanic Heat Transport
The combined atmospheric and oceanic circulations transport
the net excess heat of the tropics towards the poles where
there is a net deficit of heat. (??)
5
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Convective Overturning Cells
Vertical convection results when the lower part of the
atmosphere becomes unstable. Daily solar heating of the
land creates a pocket of hot air that, because it is less
dense than the adjacent air, rises vertically in an “updraft”;
cooling as it rises. In other places (to the sides), pockets of
colder, relatively more dense air accumulates at elevation
sink. When the sinking air is rewarmed by the land and
begins to feed the updraft, a convection cell is formed and
the atmosphere is said to overturn.Overturning convection
cells also occur in the ocean waters. (UWaC?)
6
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Atmospheric Circulation on a Non-Rotating Earth
On a non rotating earth only two giant convection
cells would form, one in each hemisphere. The air
would rise near the equator, spread out and travel
towards the poles where it would sink and travel
back towards the equator where it would be heated
up and rise again. (??)
Earth Rotation Makes Single Cell System Unstable
The earth’s rotation makes the single cell (one in each hemisphere) system
unstable and breaks each hemisphere up into three cells. (UWaC)
7
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Earth Rotation
The Earth rotates counterclockwise as seen
from the North Star . (ItO)
Coriolis Deflection
The apparent and actual paths of a ball thrown beween two people riding
horses on a merry-go-round.
8
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
The Coriolis Effect
The west to east (CCW) rotation of the earth causes
the path of this plane, which is moving almost
straight southward in the northern hemisphere to
curve towards the right. (??)
Because of the rotation of the planet, the stars overhead appear to rotate
clockwise overhead. (??, ??)
9
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Observed Overhead Earth Rotation Varies
Depending on where a person is on the planet, the overheaad
rotation of the stars can appear to be clockwise, counterclockwise,
or no visible rotation at all. (??)
Coriolis Force-Induced Deflections
The magnitude of the deflection of particles moving along a trajectory
is relative to how far from the equator the particle is and increases as
the particles approach the poles. The particles deflect towards the
right of their motion in the northern hemisphere and to the left in the
southern hemisphere with no deflection at the equator. (??)
10
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
Single Cell Winds
One might think that the two convection cells that would
exist on a non rotating earth would just circulate with net
movement towards the east but… (UWaC)
Earth Rotation Makes Single Cell System Unstable
The earth’s rotation makes the single cell (one in each hemisphere) system
unstable and breaks each hemisphere up into three cells. (UWaC)
11
MAR 110: Lecture 9 Outline – Heat Budget / Atmosphere Dynamics
The Global Jet Stream
The jet stream is a narrow band of strong winds that snakes its way
around the globe along the polar front between the polar and
subtropical zones. The location of the jet stream loops strongly
influence the tracks of high and low pressure storm systems at
lower levels. (UWaC)
The Jet Stream
(top) The jet stream is a narrow band of strong winds
that snakes its way around the globe along the polar
front between the polar and subtropical zones. (bottom)
The location of the jet stream strongly influences the
tracks of high and low pressure storm systems (see
above) that are confined to the tropospheric layer
below it. (UWaC)
12