Transcript Solar Energy and Weather

Solar Energy and
Wind
Chapter 13
Earth’s Energy
Budget
Heat refers to thermal energy that is
transferred from one object to
another.
Mechanisms for heat transfer are
conduction, convection and
radiation
Radiant energy from the sun is
really electromagnetic radiation
Earth’s Energy
Budget
The solar radiation received
includes a little UV(ultraviolet
radiation), all of the visible light
spectrum, and a little infrared
radiation. See EM spectrum p. 423
text
Radiant Energy
Reaching Earth
The amount of solar energy
reaching the outer atmosphere is
1367 J/m2 s
Some energy is reflected back into
space and the rest is absorbed
either by the atmosphere or by the
surface
Earth’s Constant Temp
The earth must dissipate some of
the energy it receives since the
average temperature remains
relatively constant over the years
Where does the energy go?
It is radiated back into space.
Energy transformations occurring
between the absorption and
emission of IR (infrared radiation)
drive our weather systems
Energy & Water
Approximately 30% of earth’s
surface is land and 70% is water so
most of the incoming radiation
impacts the oceans.
Should we then say Planet Water
instead of Planet Earth?
What is it about water that
moderates our climate?
Specific Heat Capacity
Defined as the amount of heat
required to raise the temperature of
one gram of a substance by one
degree Celsius
Symbolically
Q = mc∆T
Q = amount of heat in Joules
m = mass in grams
c = specific heat capacity in J/g◦C
∆T = temperature change on C◦
Specific Heat Capacity
Note that fresh water and salt water
have high heat capacities. For fresh
water it is 4.18 J/g◦C
For salt water , it is 3.89 J/g◦C
What this means is that it takes a
fair amount of energy to change the
temperature of water thus large
bodies of water tend to moderate
our climate
Heat of Vaporization
A second property of water enabling
moderate temperatures is the heat
of vaporization
This refers to the amount of energy
required to convert 1.0 g of a
substance from a liquid state to a
gaseous state. If a gas condenses
back to a liquid, then the same
amount of energy is released as
heat
Heat of Vaporization
and Heat of Fusion
Q = m∆Hvap° where ∆ Hvap° is the
heat of vaporization
For water , ∆Hvap° is 2260 J/g
Q= m ∆H°fus where ∆H°fus is the
heat of fusion.
The heat of fusion refers to the
amount of heat that is required to
melt 1.0 g of a solid into a liquid e.g.
ice into water
Water in the Air
Refer to Fig 13.8 on p. 431 in text
Clouds, fog, and mist are made up
of liquid water. Just above the kettle,
there is water vapour- the gaseous
form of water. As you drive your car
in the fog or mist with your wipers
operating, you can see the water
droplets condense when they
contact your windshield. Warm air
can hold more water vapour than
cold air. Why is this so?
Re: Why does warm air hold more
water than cold air?
Date: Mon Oct 18 07:57:29 1999
Posted By: Rick Neuherz, , meteorology, National Weather Service
Area of science: Earth Sciences
ID: 938043298.Es Message:
In a technical sense, it is not true that warmer air "holds" more water
vapor than cold air. Actually, it is the temperature of the water vapor itself
that governs the amount of water vapor that may be held in the
atmosphere. The warmer the water vapor, the greater its maximum vapor
pressure. Vapor pressure is the portion of atmospheric air pressure
attributable to water vapor. The greater the maximum (saturation) vapor
pressure is the greater the capacity of the mixture of air and vapor to hold
water vapor. Since the amount of water vapor in the air is quite small
compared to the rest of the gases in the atmosphere, the temperature of
the water vapor is governed by the temperature of the rest of the air in
which it resides. This leads to the somewhat inaccurate but very
convenient notion that warmer air holds more water vapor.
Water in the air
When there is as much water
vapour in the air as possible, the air
is said to be saturated. If the air
becomes cooler of if more water
evaporates, then water droplets
form around tiny dust or salt
particles in the air. These stimulate
droplet formation. The particles are
called condensation nuclei. They
also form on solids like grass.
Humidity
Humidity is the amount of water
vapour in the air.
Absolute humidity is the actual
amount of water vapour in the air
expressed as grams water vapour
per kilogram of air
Relative humidity is the percentage
of water vapour in the air compared
with the amount of water vapour
that the air would contain if it was
saturated.
The Water Cycle
• Evaporation and condensation occur
continuously in the world
• Sources of water vapour include
oceans, rivers, lakes, the ground, living
plants
• Evaporation from the oceans and other
sources moves water vapour into the
atmosphere. Condensation leads to
cloud formation and precipitation which
falls back to the ground. Runoff from
rivers, lakes and waterways takes the
water back to the oceans. This is how
water cycles through the environment
The Water Cycle
Interactions of Solar Energy with
Land and Air
• The high specific heat capacity of water
compared to sand and the depth of
penetration of solar energy in both media
explain why there is a large temperature
difference between sand and water when
both are exposed to the same amount of
solar energy
• Heated land or water transfer some of their
thermal energy to the particles of the air close
to the surface by conduction. Molecules
collide and a temperature of the lower level
air rises. As the air warms, it expands, rises
as it is less dense and colder denser air takes
its place. This is convection. Incoming
shortwave radiation heats the ground, energy
is absorbed and longer wavelength ingrared
radiation is re-radiated to the air and is
absorbed by water vapour and carbon
dioxide. See text p. 439
Creation of Wind
• Uneven heating of air creates
wind. Wind is just air in motion.
Solar heating warms the air, its
particles become more energized
and less dense as they are farther
apart. Cooler denser air exerts
pressure on the lighter air and
pushes it out of the way thereby
creating wind.
Sea and Land Breezes
• During the day, the sun shines,
warms the land and sea. The land
warms more quickly, the air above
it warms and rises. The cooler air
above the ocean sinks and moves
in to replace the air above the
land. The warmed air expands
and cools and a convective cycle
forms. This is a sea breeze.
Sea and Land Breezes
• At night, the dry land cools faster
than the water in the oceans.
Why? The warmer air above the
ocean rises becomes more dense
and then cools. The cooler,
denser air sinks to the land and a
convective current is set up again.
This is a land breeze. See p. 441
Regions of the atmosphere
• Think “t s m t” – tell someone
marchand’s terrific
• Troposphere 0-10 km (approx)
• Stratosphere 10-50 km (approx)
• Mesosphere 50-90 km (approx)
• Thermosphere 90-500 km
(approx)
• See temp chart p. 442
Regions of the atmosphere
• Most weather occurs in troposphere. Temp
drops to ≈ -60C
• Stratosphere characterized by ozone layer
which protects us from harmful UV radiation
• Mesosphere temp ≈ -100C at top. Meteors
usually penetrate this far them burn up before
reaching the bottom of the mesosphere
• Thermosphere- temp rises to about 600 C at
the top of thermosphere 500 km above
surface.
• Presence of ionosphere straddles the upper
mesosphere and thermosphere..
• Consists of charged particles which bend
radio waves (longwave). Satellites must use
shorter wavelength microwaves for
communication.
Aurora Borealis
www.public.iastate.edu/~sdk/fick2003/
october.html
Aurora
• Borealis in Northern Hemisphere
• Australis in Southern Hemisphere
• Due to energetic charged particles
coming from the sun that are
trapped in the Earth’s magnetic
field. They spiral down to the
atmosphere colliding with gases
in the atmosphere and giving off
light of different colours.
Atmospheric Pressure
• Because the atmosphere is so thick
and because air has density and is
acted on by gravity, the lower layers
are more compressed and exert
pressure on the surface and objects at
the surface.
• Atmospheric pressure has been
standardized at 101 300 Pascals (i.e.
N/m2) for dry air at sea level at
25˚C.Note this is 101.3 kPa
Gases in the Atmosphere
Nitrogen
Oxygen
Trace
Greenhouse gases (GHG’s)
• Carbon dioxide (comprises 0.03% of
the gases in the atmosphere)
• Chlorofluorocarbons (CFC’s)
• Methane
• Dinitrogen oxide
• These are important as they trap
infrared radiation and warm the
atmosphere before the energy
escapes the Earth into space.
• Too many GHG’s are already causing
global warming.