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Clear day in early Sep, say Sep 2-3rd the UV max was still hitting "8"
This is about 20 days before the Autumn equinox.
20 days after the Spring Equinox would bring you to April 11-12th.
The UV max on a clear day that time of year is like 5, maybe 6.
Our first UV max of 8 "always" seems to happen after May 1st, perhaps as early as the last 3-4 days of April.
And the dewpoints in mid-April are a lot lower than in early Sep.
Does this have to do with the sun being closer to the earth in the northern hemisphere summer?
Is the sun angle higher 20 days before the autumn equinox vs. 20 days after the spring equinox?
I'm guessing because the sun is "stronger" as we transition from summer to fall than it is when we transition from winter to spring. I think that's partly why September is much warmer than March.
I wonder if it has to do with the fact that the sun is actually closer to the Earth in the Northern Hemisphere winter than in the summer. Due to this, the Earth gets a slightly higher dose of UV rays in the Northern Hemisphere... I'm probably completely wrong on this but it's my best guess.
It also explains why generally in the southern hemisphere the UV indices are a bit stronger during summer than in the Northern Hemisphere (in addition to the weaker ozone layer at higher latitudes in the southern hemisphere).
If someone can find out how much difference the distance to the sun makes, and details of its track, it'd be appreciated.
Unrelated,
I can see now why our summers are prone to so much rain and cloud; avg of 15 days with some precip May-Jun.
Our swimming season sure looks short!
If someone can find out how much difference the distance to the sun makes, and details of its track, it'd be appreciated.
Unrelated,
I can see now why our summers are prone to so much rain and cloud; avg of 15 days with some precip May-Jun.
Our swimming season sure looks short!
According to Wikipedia, the Earth makes its closest approach to the sun around January 3 (Perihelion) and its furthest approach around July 4 (Aphelion). The difference between the two is approximately 5 million kilometres which translates roughly to a difference of 6.9% of solar energy reaching the Earth. To me, that's a significant difference. It could account for the discrepancy for the varying levels of UV radiation.
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