purple the major factors in strength of UV are:
- latitude; the nearer the equator you are, the less atmosphere the rays have to pass through as they come from nearer straight up.
- altitude: the higher up in the atmosphere you are, the less atmosphere there is above you to shield you
- time of year, which combined with latitude also affects the apparent height the sun reaches in the sky.
the tilt of the earth is the cause of the seasons and the change in the apparent height of the sun during the year.
things cool down at dawn and dusk because the apparent height of the sun decreases, obviously ending in it going below the horizon.
the earth is actually closer to the sun during the northern hemisphere winter - the orbit is an ellipse. Doesn't make much difference comparted to the other effects.
if UV strength and temperature were linked no-one would come back from a ski trip looking like a toffee apple. Or get burnt on a snowy day in the UK (reflection)
it is all fairly basic stuff - and you don't need to be a 'science person' you need not to have flicked your hair through school physics/geography wherever the fact that the earth is tilted and goes round the sun is taught.
what annoys me are the endless cries of 'it's hot, so I must wear suncream' (or worse, thinking it only needs to go on the kids when it is hot). More skin is exposed when it is hot but most of us always expose our faces. The problem is that this attitude means people have no understanding that peak UV is June 21st, not August in the school holidays. Of course August needs protection too.