Insolation over the Globe

1. Insolation over the Globe - insolation (incoming solar radiation) is a flow rate of solar energy - measured in units of watts per square meter (Wm2) - varies by latitude and by season S&S Figure 2.5, p. 57

2. Why do we have seasons? the four seasons occur because the Earth maintains a constant orientation (tilted 23½° with respect to the perpendicular to the plane of the ecliptic) as it revolves around the sun S&S Figure 1.17, p. 40

3. Insolation intensity & incidence angle the angle of the Sun’s energy determines the intensity of insolation on the ground for square B, the same amount of energy as represented by square A is spread over a larger area (b x c) on the ground and therefore represents a lower insolation intensity than area a x c S&S Figure 2.6, p. 57

4. Sun’s path: seasonal insolation & latitude • the sun’s path across the sky varies in position and height above the horizon seasonally • Thus insolation intensity & duration vary Equator S&S Figure 2.7c, p. 58

5. Mid-latitudes have more variable seasonal insolation Columbus, OH • Equinoxes - at noon the Sun is 50 degrees above horizon • Solstices - June solstice has a higher angle than the December solstice S&S Figure 2.7b, p. 58