1. The Earth’s Atmosphere: Factors That Affect the Weather SOL 6.6

2. We have learned that virtually all of Earth’s weather takes place in the lowest level of the atmosphere called the troposphere. This is due in part to the amount of heat, water, and air pressure found at this level.

3. Heat energy, water vapor, and air pressure determine the weather conditions on Earth.

4. Let’s investigate how these three factors determine the weather. We know that the unequal heating of the Earth’s surface by the sun causes a rising and falling air pattern called convection. (vertical movement)

5. Convection distributes heat energy in the troposphere as warm air rises and cooler air falls.

6. In addition to rising and falling, air also moves horizontally. This horizontal movement is caused by differences in air pressure. Air tends to move from areas of high pressure to areas of low pressure. This horizontal movement of air due to air pressure is called wind.

7. These vertical and horizontal movements of air are connected. This is true because differences in air pressure are caused by the unequal heating of the Earth’s surface.

8. When an area of the Earth is heated by the sun, the air above it heats up, too. As air heats up, it expands, becomes less dense, and rises. Cooler, heavier air nearby will then move horizontally (wind) under the heated air causing it to rise even more. The greater the pressure differences are between two locations on Earth, the faster the winds.

9. Added to this moving mix of heat and pressure is water vapor. The amount of water vapor or moisture in the air is called humidity. As the bodies of water on Earth are heated by the sun, water molecules escape into the air in the form of water vapor (evaporation). This water vapor rises with the heated air in a convection current into the troposphere. As this humid air rises into the cooler regions of the troposphere, the water vapor cools down and changes into minute, condensed water particles. As more and more of these condensed water particles join together, a cloud is formed.