Why do we experience Daily and Seasonal Temperature Changes?
On Earth we experience distinct patterns of temperature change that we have all noticed.
- Daily Temperature Patterns
- Seasonal Temperature Patterns
Both of these changes are caused by changes in the angle of insolation, or in other words the angle of the Sun's rays striking the Earth.
Angle of insolation
ANGLE OF INSOLATION IS THE ANGLE AT WHICH SUNLIGHT HITS THE EARTH
When the Sun is directly overhead:
- insolation strikes the Earth at a high angle
- more energy is contained in a smaller area
- hings to heat up quickly.
When the Sun is not directly overhead
- insolation strikes the Earth at a lower angle
- This means its energy is spread out over a larger area
- which makes things heat up much more slowly.
This explains why different parts of the Earth have different temperatures.
- THE EARTH'S POLES ALWAYS HAVE LOW ANGLE OF INSOLATION, SO THEY ARE ALWAYS COLD
- THE EQUATOR ALWAYS HAS A HIGH ANGLE OF INSOLATION, SO IT IS ALWAYS WARM
This relationship is extremely important to understanding climate patterns. Put simply:
The Higher the Angle of Insolation...the Higher the Temperature!
Daily Temperature Pattern
At night, no sunlight is hitting the Earth. Obviously, this means that no insolation is being absorbed, so the Earth cools down. The coldest part of everyday is just before sunrise, because at this point it has cooled down for hours throughout the night.
- When the Sun rises in the East, and it peeks up above the horizon it is very low in the sky, so the angle of insolation is low
- As a result the morning is usually cooler
- At noon, the sun is at its highest point in the sky.
- This means the angle of insolation is highest at noon, so we absorb the most insolation at noon.
- However, it takes some time for the Earth to absorb that insolation and re-radiate it as infrared (heat).
- This means there is generally a 2-3 hour delay between noon when we absorb the most insolation, and the early afternoon when it is hottest.
- After noon, the Sun starts to sink back down to the West.
- As it does this the angle of insolation begins to decrease
- As a result the temperature starts to drop in the evening
Seasonal Temperature Pattern
Earth experiences seasonal changes for 2 reasons.
1. The Earth's axis is tilted 23.5 degrees from vertical.
2. The Earth revolves around the Sun.
These two factors have the combined effect of changing the angle of insolation we receive throughout the year.
- During the winter, the Northern Hemisphere is tilted away from the Sun.
- As a result we have a lower angle of insolation.
- As a result we experience lower temperatures.
- During the summer, the Northern Hemisphere is tilted towards the Sun.
- As a result we have a higher angle of insolation.
- As a result we experience higher temperatures.
Spring and Fall
- During spring and fall, the Northern Hemisphere is not tilted towards the Sun, nor away from the Sun, but somewhere in the middle.
- As a result we have a medium angle of insolation.
- As a result we have medium temperatures during spring and fall.