Sun's heat on Earth in summer and winter

[Graeme M]

That's an interesting comment Irol. I haven't gone back to review the other comments on this thread but it does raise a good point in relation to my original post. What part of the spectrum carries 'heat'? I am pretty fuzzy on the physics of this but does sensible light necessarily have the highest effect in terms of heating an object? Is it likely that other less visible frequencies (eg UV) are more efficient at heating and are more intense during summer than winter? Why should there be less UV in winter than summer?

Which leads me to wonder. The Earth's atmosphere must attenuate the sun's rays a LOT. I know that the moons surface temp in full sun is very high (120C) yet even in desert conditions ambient temperature on Earth are never that high. However that is not an apples and apples comparison, because the moon's surface is the actual ground. What temperature does the desert sand in say the Gobi desert reach? Obviously the sand radiates off heat but then again, air temps have never exceeded what? 60C?

I wonder what a Stevenson Screen would measure on the moon?

 

[Baluncore]

Why should there be less UV in winter than summer?

Fundamentally, because the path through the atmosphere is longer and so there is more absorption. You also expect less UV early in the morning and late in the afternoon for the same path length reason. Likewise UV is also higher in the mountains and at lower temperatures.

There are some counter effects and complexities. The ozone hole over the poles breaks up and moves towards the tropics over summer. That permits more UV to pass in summer. In the tropics, UV levels may be more dependent on atmospheric temperature, that is because more water vapour can be dissolved in warmer air. Below –20°C there is very little water vapour in air.

 

[fayn]

sorry for resurrecting an old thread but i think it is closely related to what i want to ask. Imagine the situation (i have so expertly drawn) below in real dimensions. 2 people hold a plate exactly perpendicular to the sun rays, the plates are the same size. Which one catches more energy and why? From experience I think A should receive radically less energy (otherwise it wouldn't matter if solar power plants are built on equator or on arctic circle if the PV cells track the sun), but i don't know why. Is it just because of the longer path through the atmosphere? A is also further from sun but i think the ~6400km are negligible.

 

[Bystander]

longer path through the atmosphere?

Yes.

 

[Baluncore]

Welcome to PF.
Yes, atmospheric path length and cloud is by far the most important.

A is also further from sun but i think the ~6400km are negligible.

That may be true for the inverse square law applicable to radiation, but the tides are driven by the inverse cube. Neglect that difference at your cost, and you may be washed away by the rising tide, driven by that very small difference.

 

[fayn]

Yes.

Welcome to PF.
Yes, atmospheric path length and cloud is by far the most important.

thanks for the answers, now that i look at it it really seems logical.

 

[russ_watters]

thanks for the answers, now that i look at it it really seems logical.

Well, there's another important issue here too: if you want to build a solar array of any decent size in the arctic circle, to arrange it as in your picture would require mounting it vertically on a large tower! (or use a very long, skinny piece of land).