We all know it gets cold in the winter, but do you know why? There are really a number of factors, but it all goes back to the simple energy balance diagram and the First Law of Thermodynamics. When it's hot, more energy is coming in than goes out and when it's cold, more goes out than comes in. But, why does it change from month to month, and what are some of the effects of the energy balance on our environment?
I. Energy Balance again
A. Planetary vs. local balance
II. Controls on local energy input -- warming the atmosphere
A. Solar distance
B. Solar position in the sky
1. Angle of incidence
2. Tropics and arctic/antarctic circles
III. Other factors
A. Radiation out
B. Ground and water temperature
C. Surrounding air masses
Objectives/Questions
1. Explain why Philadelphia receives more energy on July 1 than on Jan 1.
2. Explain why the Tropic of Cancer receives more energy than the Equator on July 1.
3. Draw a circle representing the Earth. Place the Equator and N and S pole on the circle. Show the angle of incidence at the tropic of Capricorn, the Tropic of Cancer, the Arctic Circle, the Equator and 40° N latitude on March 21 and on June 21.
4. Explain the effect that a large body of water will have on the heating and cooling of the atmosphere above it.
5. Explain the effect that vegetation might have on the heating and cooling of the atmosphere above it.
6. During the summer, temperature in a city is often cooler during the day and much hotter during the night than the temperature in surrounding rural areas. Use the First Law of Thermodynamics to help explain why this pattern is so common.
7. Our winter temperatures are strongly affected by arctic air
masses but in the summer time arctic air masses aren1t nearly as
important. Provide a likely explanation for this difference.