Background to the question is I’m from Melbourne Australia but was raised inland where it gets really hot in summer.
A couple of weeks ago I was in Las Vegas. The temperature in the middle of the afternoon was around 45c/110f for the first few days I was there and after a couple of days I made 2 specific but possibly unrelated observations.
I didn’t get sunburned. I walked around the strip in the full sun wearing shorts, singlet, not hat no sunscreen for easy an hour or more per day and didn’t burn or get tanned. I have blonde hair and a fair complexion. 30 minutes mowing the lawn shirtless on a warm spring day would get me more colour on the shoulders that I got in hours of walking around in the sun in Vegas.
I asked a work colleague who visited Vegas recently and she made a similar observation. Another colleague who lived in San Francisco for a few years some time back made the comment that the Ozone layer is thinner over Australia so we get more UV and whatever else rays. More sunburn, more skin cancer. Is that factual or a myth? Is what I observed a real phenomenon or just fluke? If it’s real what is the cause?
Similar but different, the temperature while I was there was no doubt hot but did not seem to me to be as hot as the same temperature would be at home. Maybe the relative humidity was a factor, 45c/110f in Melbourne is horrible as it’s also humid. We get those sort of days 3 or 4 times a summer if we’re unlucky. Up inland where I was raised however we get that sort of weather for weeks on end over summer with usually very low humidity, so it’s similar to Vegas weather, but feels hotter.
Temperature is taken in the shade so it may be that the same phenomenum in point 1 is at play here or it could be something totally different but 45c/110f felt more like 35c/95f. Hot but pleasant.
So, I’m after a genuine answer as to whether there is some climactic or atmospheric quirk or something that would account for basically why the sun over vegas seemed to have far less sting than the sun over Australia.
One slight difference is that the earth’s orbit around the sun is not circular - it is an ellipse. The earth is actually closer to the sun during the southern summer and vice-versa. So southern summers are slightly hotter.
Quick wikipedia cut-and-paste:
‘The difference in distance between Earth’s nearest point to the Sun in January and farthest point from the Sun in July is about 5 million kilometers (3.1 million miles). Earth is about 147.1 million kilometers (91.4 million miles) from the Sun at perihelion in early January, in contrast to about 152.1 million kilometers (94.5 million miles) at aphelion in early July. Because of the increased distance at aphelion, only 93.55% of the solar radiation from the Sun falls on a given square area of land than at perihelion. As winter also falls in the southern hemisphere at the same time as aphelion, this decrease in solar radiation due to the aphelion plus shorter periods of daylight causes, in general, less heat from the Sun to hit the southern hemisphere in winter than solar radiation hitting the northern hemisphere during its winter at perihelion six months later.’
But I don’t think it actually makes THAT much difference.
So the net result of that is - possibly my received wisdom isn’t really true. But I do see that UV varies a lot month to month, and also that 45 degrees is what I’d call bloody hot for just getting into autumn. I’m pretty sure that it’s the UV that actually determines how fast you burn. So perhaps the very high temperature made you feel like the UV ought to be at midsummer levels whereas, in September, it’s actually quite a few points lower, thus burning you less?
It’s not exactly what you are asking, but here is a picture of solar insolation – the amount of sun intensity over the world as published by a solar power company.
Solar Insolation depends on how many hours of sun you get, not just how intense the sun is, but I haven’t found a map of “peak” solar insulation
I was there for basically the last week of August. End of summer, so I suppose the UV was on the wane a bit from the middle of summer, but it still didn’t make sense to me.
When I’d go for a shower before dinner I kept expecting to see a pronounced singlet line in the mirror and next to nothing. The amount of time I was in direct sunlight just didn’t make sense with the utter lack of sunburn, hence why I’m asking
Local ozone could also make a difference. Ozone doesn’t have to be in the upper atmosphere to absorb UV; it’ll do it anywhere. Ozone is produced by auto engines, although modern ones are engineered to keep it to a minimum. But still, enough cars will produce significant amounts locally, especially near high volume roads.
I would imagine that if you have enough pollution in the air to produce enough ozone to have any effects, it would be outweighed by the simple shading effect of particulates.
Yes there may be difference.Ultraviolet radiation is the process in which shorter electromagnetic energy is transferred from one place to other. but there is typically from the sun through the earth’s atmosphere to the earth surface. Less typically from a tanning bed lamp to a person skin
No doubt. I remember reading something similar to the OP, except about Mexico City. The person was a scientist, although I forget what specialty, who had to be outside in that city during a full day. He was bald and had forgotten to pack a hat. Yet he got no sunburn. He attributed it to local ozone, but it probably could have been other polution.
I remember being surprised to read in an interview that the West Indian cricketers had to be careful about their exposure to the sun in Australia because it was the only place they got sunburns while playing.
Isn’t (most of) Australia plenty closer to the equator than Las Vegas? The closer to zenith the sun rises, the higher will be the incoming effect (by a factor of cos heta).
