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In order to understand the weather patterns we observe on our planet, we need to understand what causes them in the first place. Factors such as the composition of the atmosphere, the materials on the surface of the earth, and the different types of heat transfer affect weather across the planet.
Direct and Indirect Sunlight at the Equator and Poles
As we have looked at weather systems, we have seen that Polar winds (coming from the poles) are colder and the Tropical winds (coming from the equator) are warmer. But why is there such a difference between the temperature at the equator and the poles?
As the Earth orbits the sun, the sun's rays strike the areas near the Equator at a more direct angle. This delivers more energy at the equator, than it does at the poles. It also means the poles are generally colder than the equator.
When sunlight shines on the Earth at a lower angle (such as at the north and south pole), the energy of the sunlight is spread over a larger area, and is therefore weaker than if the sun is higher overhead and the energy is concentrated on a smaller area (such as at the equator).
Flashlight Lab
A breakdown of the ideas behind the flashlight lab that we did in class can be found at this link.
Electromagnetic Spectrum
Electromagnetic waves are invisible forms of energy that travel though the universe. However, you can "see" some of the results of this energy. The light that our eyes can see is actually part of the electromagnetic spectrum.
This visible part of the electromagnetic spectrum consists of the colors that we see in a rainbow - from reds and oranges, through blues and purples. Each of these colors actually corresponds to a different wavelength of light.
Electromagnetic spectrum
The sound we hear is a result of waves which we cannot see. Sound waves need something to travel through in order for it to move from one place to the next. Sound can travel through air because air is made of molecules.
These molecules carry the sound waves by bumping into each other, like dominoes knocking each other over. Sound can travel through anything made of molecules - even water! There is no sound in space because there are no molecules there to transmit the sound waves.
Electromagnetic waves are not like sound waves because they do not need molecules to travel. This means that electromagnetic waves can travel through air, solid objects and even space. This is how astronauts on spacewalks use radios to communicate. Radio waves are a type of electromagnetic wave.
Electricity can be static, like what holds a balloon to the wall or makes your hair stand on end. Magnetism can also be static like a refrigerator magnet. But when they change or move together, they make waves - electromagnetic waves.
Electromagnetic waves are formed when an electric field (which is shown in red arrows) couples with a magnetic field (which is shown in blue arrows). Magnetic and electric fields of an electromagnetic wave are perpendicular to each other and to the direction of the wave.
When you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves. Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength. Wavelength is the distance between one wave crest to the next.
Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom.
Types of Heat Transfer
Step 1: Radiation
Radiation from the sun travels to the Earth and heats Earth's materials.
Step 2: Conduction
The warm ground heats the air touching it.
Step 3: Convection
The warm air that was touching the ground rises and the cool air sinks.
The heat source for our planet is the sun. Energy from the sun is transferred through space and through the earth's atmosphere to the earth's surface. Since this energy warms the earth's surface and atmosphere, some of it is or becomes heat energy. There are three ways heat is transferred into and through the atmosphere:
- Radiation
- Conduction
- Convection
Radiation
If you have stood in front of a fireplace or near a campfire, you have felt the heat transfer known as radiation. The side of your body nearest the fire warms, while your other side remains unaffected by the heat. Although you are surrounded by air, the air has nothing to do with this transfer of heat. Heat lamps, that keep food warm, work in the same way. Radiation is the transfer of heat energy through space by electromagnetic radiation.
Most of the electromagnetic radiation that comes to the earth from the sun is invisible. Only a small portion comes as visible light. Light is made of waves of different frequencies. The frequency is the number of instances that a repeated event occurs, over a set time. In electromagnetic radiation, its frequency is the number of electromagnetic waves moving past a point each second.
Our brains interpret these different frequencies into colors, including red, orange, yellow, green, blue, indigo, and violet. When the eye views all these different colors at the same time, it is interpreted as white. Waves from the sun which we cannot see are infrared, which have lower frequencies than red, and ultraviolet, which have higher frequencies than violet light. It is infrared radiation that produce the warm feeling on our bodies.
Most of the solar radiation is absorbed by the atmosphere and much of what reaches the earth's surface is radiated back into the atmosphere to become heat energy. Dark colored objects, such as asphalt, absorb radiant energy faster that light colored objects. However, they also radiate their energy faster than lighter colored objects.
Conduction
Conduction is the transfer of heat energy from one substance to another or within a substance. Have you ever left a metal spoon in a pot of soup being heated on a stove? After a short time the handle of the spoon will become hot.
This is due to transfer of heat energy from molecule to molecule or from atom to atom. Also, when objects are welded together, the metal becomes hot (the orange-red glow) by the transfer of heat from an arc.
This is called conduction and is a very effective method of heat transfer in metals. However, air conducts heat poorly.
Convection
Convection is the transfer of heat energy in a fluid. This type of heating is most commonly seen in the kitchen when you see liquid boiling.
Air in the atmosphere acts as a fluid. The sun's radiation strikes the ground, thus warming the rocks. As the rock's temperature rises due to conduction, heat energy is released into the atmosphere, forming a bubble of air which is warmer than the surrounding air. This bubble of air rises into the atmosphere. As it rises, the bubble cools with the heat contained in the bubble moving into the atmosphere.
As the hot air mass rises, the air is replaced by the surrounding cooler, denser air, what we feel as wind. These movements of air masses can be small in a certain region, such as local cumulus clouds, or large cycles in the troposphere, covering large sections of the earth. Convection currents are responsible for many weather patterns in the troposphere.
Heating of Earth's Different Materials
The surface of the Earth is made of a variety materials which will heat up differently. For instance, on hot summer day where would you rather stand barefoot? Some grass or in the middle of a street? Most of us would choose the grass, but why? Both areas are receiving the same amount of sunlight but the temperature of the grass does not increase as quickly as the temperature of the asphalt that the street is made of.
Some of the the main types of materials covering the surface of the earth are dirt/soil, sand, snow/ice, water, cement, and even roof shingles. (Think about all the rooftops covering places where there are a lot of people living) Each of these materials heats up differently. Dark soil, cement and roof shingles tend to have larger and faster increases in temperature. Whereas things such as snow and water tend to have smaller and slower increases in temperature.
Think about what kinds of materials are usually found in a city. Our sidewalks and streets are made of cement and asphalt and our roofs are covered in dark shingles. This can cause the temperature of the atmosphere (air) around a city to increase much more quickly than other areas without these types of materials.
Interestingly materials the heat up quickly also tend to cool down quickly when there is nothing to heat them up. Things that would heat up slowly would also cool down more slowly and retain what heat they do have for longer.
The graph above shows two different materials. The one in red would be a material that heats up quickly, such as shingles or sand, and the one in blue would be a material that heats up slowly, such as snow or water.
The red line increases in temperature very fast compared to the blue line and it also gets hotter. However, when it cools down it cools down much faster than the other material which takes much longer to lose its heat.
Think about going to the beach. During the day the sand gets so hot that it feels like it is burning your feet. You can cool off your feet by running into the water. Even though both are getting the same amount of sunlight the sand heats up much faster than the water.
What about if you were to go the beach late in the evening? By then the sand might actually feel cold and the water warm. Since the sand heated up so quickly it will also cool off much faster. So the sand loses its heat and feels cold and the water holds the heat for longer.
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