Climate Review
Climate is a very complex interaction between global factors. The biggest factor in global weather is the uneven heating of the Earth's surface. The equator receives more light/heat year round than any other region on Earth. The Poles receive the least light/heat. Hot air rises and cooler air moves in to take its place. This interaction of the uneven heating between the equator and poles, plus the coriolus effect, is responsible for Earth's most reliable winds (easterly trade winds and westerlies that allowed booming trade by sailing ships between America and Europe). In addition, water is an enormous heat sink. This means that it takes a lot of energy to heat water, and when it cools water releases a lot of energy.
Liquid water, in lakes and oceans, will heat or cool the air above it. On a hot day on the beach air warm air will become less dense and rise from the ground, pulling cooler, denser air from over the water on land. This is a sea breeze. At night, when the land cools and the warmer air is over the ocean there will be a land breeze.
Air masses move in fronts. An air mass that forms over land is dry, and a mass that forms over water is humid (carrying a lot of evaporated water). Tropical air masses are warm and polar air masses are cold. For example, an air mass that forms over Canada and moves to the United States would be cold and dry. When a cold front passes it will get windy and temperatures will drop. An air mass that forms over the Gulf of Mexico could travel to Texas and bring us warm, moist air. A warm front will bring warm humid air. High pressure is generally associated with fair weather and light winds, low pressure stormy, windy weather. A traditional scale used by sailors for wind speed is the Beaufort Scale.
When a cold front collides with warm moist air,, the warmer air will be rapidly forced over the cold front where it will cool, water vapor will condensate into liquid and fall as precipitation in a thunderstorm. Thunderstorms have a characteristic thunderhead, anvil shaped, cloud. The vertical billowing shape comes from strong updrafts of warm humid air. Strong convection currents can result in tornadoes which are categorized by the amount of damage they do in the Fujita scale. When a warm front collides with cool air, it rises over the cold air more slowly, cools more slowly and falls as a more gentle rain.
Hurricanes are gyres that form in the Atlantic Ocean, near Northwestern Africa. They start as storms called tropical depressions. As they move across the Atlantic they gain energy and become tropical storms, and finally hurricanes. Since hurricanes are powered by energy from warm ocean water, they start to lose energy as soon as they run aground.
Review Questions
- 1. What astronomical body powers weather on Earth?
- 2. What are global convection currents? What causes them?
- 3. Describe land and sea breezes.
- 4. Describe convection currents in terms of energy in a fluid.
- 5. Rain is most correlated with (low/high) pressure. Clear skies and fair weather are correlated with (low/high) pressure.