Solar Energy and WindChapter 13

Earth’s Energy BudgetHeat 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 BudgetThe 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 EarthThe 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 TempThe 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 CapacityDefined 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 AirRefer 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 1999Posted By: Rick Neuherz, , meteorology, National Weather ServiceArea of science: Earth SciencesID: 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 airWhen 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 Borealiswww.public.iastate.edu/~sdk/fick200

3/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.