Five reasons why there are seasons
In our last article, we looked at insolation and the solar constant, and in this article, we are going to look at global net radiation and seasons.
Net global radiation is the balance between incoming shortwave radiation from the sun and outgoing long-wave radiation from the Earth, as measured at the top of the atmosphere.
We have surpluses of radiation in the equatorial regions and a deficit poleward north and south of 36 degrees latitude.
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The areas with the greatest gains of radiation are over the Pacific and Indian oceans, right along the equator. The largest deficit of radiation is over Antarctica.
By looking at this simple picture of global net radiation, we can see the basics of what causes most of the weather around the world.
We have a surplus of energy in the equatorial regions, while we have strong deficits in the polar regions. Weather is a result of the Earth trying to even out this imbalance.
Unfortunately, it is not that simple — there are plenty of other factors that we must look at to really understand the big picture.
The first item to look at are seasons: spring, summer, fall and winter.
Most of us have a basic understanding of what causes the seasons, but there are five reasons for the seasons: revolution, rotation, tilt, axial parallelism and sphericity.
Let’s start with revolution, which is the Earth’s orbit around the Sun.
The Earth’s revolution, which takes 365.24 days, determines the length of each season.
Then we have the Earth’s rotation. Without our Earth rotating, the whole planet would basically have six months of daylight and six months of darkness.
Due to our rotation, which takes approximately 24 hours to complete, we have 365 days in a year.
Next up is axial tilt.
To picture this, imagine that the Earth is a spinning top that is doing a large orbit around the sun.
Now, instead of picturing that top standing straight up and down, picture it leaning to one side, at an angle of about 23.5 degrees.
This means that one end of the Earth is pointing toward the sun, while the other end is pointing away from the sun. It explains why different parts of the Earth have differing amounts of daylight.
To tie this into the seasons, we need to look at axial parallelism, which means that while the Earth is a spinning top tilted to one side, it is always tilted in the same direction.
So, as the Earth revolves around the sun, the tilt of the Earth remains in a constant direction, which means that for half of the year the southern part of our planet is pointed toward the sun and during the other half, the northern part is pointed towards the sun.
The fifth reason for seasons has to do with the fact that the Earth is a sphere, which results in an uneven receipt of incoming solar radiation.
Next issue, we’ll look at the latest long-range forecasts for the spring and early summer before we return to look at the composition of the atmosphere.
Source: producer.com