Indirect and Direct Light
Remember the flashlight!
Also remember that this picture to the right is not an accurate representation of Earth’s orbit, but, instead, is intended to show why we have seasons. See how, in the winter, North America is pointed away from the sun rays. Most of the light rays from the sun are hitting the Southern Hemisphere. The indirect light, or more spread out like the flashlight example, falls on North America in the winter.
It is colder in the winter because we receive less intense light from the sun. In the summer, North America is pointed toward the sun, and we receive the most intense light. Therefore, it is warmer.
Think of direct/indirect light like this. It is darker outside at sunrise/sunset. The sun is so low on the horizon, its light is very spread out over the land that you see. Even though the sun shines the same brightness, the section of the earth you see receives less intense light. That’s why it is somewhat dark at sunrise/sunset. It is not the full brightness that you get during the middle of the day.
Just as brightness is affected by direction of sunlight, so is the amount of heat transferring radiation. Remember that radiation is one of the heat transfer mechanisms we discussed in class. We receive less intense radiation during the winter, because of this indirect/direct idea.
The whole reasoning behind all of this is our 23.5 degree axis tilt. If Earth’s axis wasn’t tilted, we wouldn’t have seasons. Different hemispheres have to be pointed toward or away from the Sun in order to have direct/indirect light.

The Earth heats the troposphere. The Earth (the land, the buildings, the oceans) is warmed by the sun. It the transfers that heat to the lowest atmospheric zone.
Because this is the heating mechanism (mainly conduction – where the atmospheric molecules come into contact with the land), it makes sense that that troposphere gets colder as you move up in altitude.
Ultra violet radiation heats the stratosphere. The stratosphere is mainly composed of ozone. Ozone absorbs uv rays. Therefore, it makes sense that the highest altitude of the stratosphere would be the warmest. The upper altitudes absorb all of the uv radiation first. The lowest part of ozone layer receives the least amount of uv radiation (because it comes from the sun).
The mesosphere acts very similar to the troposphere. It gets most of its heat from the high temperature stratosphere through conduction. Therefore, it makes sense that the temperature in the mesosphere decreases as altitude increases. You are moving away from the stratosphere (heat source) as you increase in altitude.
The thermosphere absorbs high energy light like gamma rays and x-rays from the sun. Again, this makes sense because the highest altitude thermosphere is the highest temperature. The highest altitude absorbs the gamma rays and x-rays first
(because they come from the sun), and the lower parts of the thermosphere get the least amount of gamma and x-ray.
The atmosphere is broken up into sections of how the temperature changes in that section. There are actually no physical lines between these areas, it is only our society’s description of the atmosphere. Scientists just noticed that these four distinctly behaving areas existed, and we called them different names to describe/explain the behavior.

Conduction is the transfer of heat through touching objects. High energy molecules hit low energy molecules, thus transferring the energy from hot areas to cold areas.
This is like a pool game. The “high energy” cue ball hits the “low energy” number 8 ball. The 8 ball was previously not moving. However, when the cue ball hits it, it starts moving. The cue ball gives the 8 ball energy. The cue ball, however, suffers an energy loss.
Convection is the transfer of energy through moving gas or liquid. Air next to a fire will be heated through conduction. That air, because it is now at a higher temperature, has an increased volume and thus a decreased density. That air will move upward because it will “float” on more dense air. The more dense air is colder air. Once that cold air is heated up by the fire, it too will float away. Thus, we have a convection current, or a circularly occurring movement of air.
Radiation is light energy. Put your hand next to a bright light bulb and feel the heat being transferred to you. The Sun also radiates. This is how Earth gets most of its energy. Radiation can travel through empty space. For example, Earth receives light energy from the sun. Radiation can also travel through a gas or fluid if it is not absorbed. Remember how the stratosphere absorbs the uv rays from the sun. We know that the stratosphere doesn’t absorb all of the light from the sun, otherwise we would never have day time. Some light gets through the stratosphere to light up the world around us.

Balloon experiment:
By increasing the temperature of the air inside the balloon, the volume of the air increased. Increasing the temperature increases the volume. The same amount of mass, the number of molecules, was inside the balloon. Since density equals mass divided by volume, the density of the air decreased.
Keeping the mass the same, and increasing volume, the density = mass/volume equation shows that the density will decrease. This is why hot air always rises! It is less dense than cold air because of this temperature and volume relationship. As you know, less dense things float on more dense things. The hot air is floating on the cold air.
Yarn box Experiment:
When we went to the gym to act as air molecules, we found that pressure is also related to temperature and inversely related to volume. There were more collisions with the walls (more pressure) when we increased the temperature
(made you move faster). There were also more collisions with the walls when the volume decreased.
Temperature goes up -> volume goes up; temp down -> volume down
Temperature goes up -> pressure goes up; temp down -> pressure down
Volume goes down -> pressure goes up; volume up -> pressure down
You might be thinking that all of this can’t be true at the same time. Usually, when thinking about these things, we try to keep one of the 3 things constant. For example, if we are working with the volume and pressure relationship, we try very hard to keep to the temperature constant. Note how your car engine, a pressure and volume machine, is usually around the same temperature. If we are working with the temperature and volume relationship, we try to keep the pressure the same. Of course, in the real world, there will always be slight contributions of all 3 properties.