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Old 01-16-2011, 10:35 PM
 
Location: motueka nz
504 posts, read 488,861 times
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Is there a heat index using UV and temperature? or one that combines UV, RH and temperature? I ask because it felt so hot today, the rocks at the river were to hot to stand on (I was fortunate to be working beside a river today) and yet, it was only 24C max, but a UV index of 15 and no wind made it cook.

Where in the world would have the worst combination of temperature, RH and UV?
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Old 01-16-2011, 11:28 PM
 
Location: Paris
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Hong Kong on a sunny July day
This would be something like 33C, high humidity, and a 90 sun angle!
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Old 01-17-2011, 01:33 AM
 
Location: Cloudchurch, Subantarctica
2,608 posts, read 1,916,443 times
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Quote:
Originally Posted by Stoney63 View Post
Is there a heat index using UV and temperature? or one that combines UV, RH and temperature? I ask because it felt so hot today, the rocks at the river were to hot to stand on (I was fortunate to be working beside a river today) and yet, it was only 24C max, but a UV index of 15 and no wind made it cook.

Where in the world would have the worst combination of temperature, RH and UV?
I don't think UV is what makes the sun feel hot. The heating part of the sun is due to infra-red radiation. But obviously a high sun angle leads to higher IR and UV, so there ought to be a strong correlation. A better measure of the sun's strength is the insolation per unit area (e.g., Watts per square meter). I'm not aware of a formula for apparent temperature that incorporates the effect of solar insolation but I would be interested in this if such a formula exists.

I know the highlands of northern Queensland can get very high UV indices. Similar climates in Africa and South America could well be some of the most oppressive on earth in summer. But I don't think anything can beat Dallol or the Persian Gulf coast.
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Old 01-17-2011, 06:33 AM
 
Location: Mildura, Vic Australia
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Northern Australia has everyone beat when it comes to UV. I've seen UV levels as high as 18 in northern Queensland this summer, at low-elevation locations.
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Old 01-17-2011, 10:40 AM
 
Location: Perth, Western Australia
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They probably don't include UV because everyone's reaction to it differs.

I don't expect UV does anything to skin in the short term, unless it's causing mild damage. (which most bodies can repair)
Perhaps someone with skin "dark as coal" spends 10-20 minutes outside at UV of 18 and feels no noticeable temp difference due to UV.
It probably wouldn't make sense to describe the heat from UV as "searing" to them.
I think that's what skin reddening is supposed to be, extra blood to the surface to make "repairs." (which adds skin heat)
I have found there are people with lighter skin than me that still resists reddening more than mine does.
This could have to do with the thickness of their skin, not just pigmentation.

Infrared is also emitted from the sun,
and this is what makes the sun feel warm instantly, to all people.
It would be interesting if they could rate and forecast IR intensity.
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Old 01-17-2011, 10:46 AM
 
Location: Perth, Western Australia
9,598 posts, read 15,613,823 times
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Quote:
Originally Posted by ChesterNZ View Post
I know the highlands of northern Queensland can get very high UV indices. Similar climates in Africa and South America could well be some of the most oppressive on earth in summer. But I don't think anything can beat Dallol or the Persian Gulf coast.
Look at this!

UV Index | SunGard Australia (http://www.sungard.com.au/uv-index - broken link)

The worst parts of Oz go pink in summer... Chile goes white! (off the charts?)
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Old 01-17-2011, 10:57 AM
 
Location: Yorkshire, England
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It's not off the charts, UV 18 is white on that scale. Great map, by the way. Shows well how my part of the world goes dark blue and almost black, not that the sun ever shines in winter anyway. I like the way Greenland in summer has a similar UV to the UK despite being 10 degrees further north, probably because of reflection from glaciers.
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Old 01-17-2011, 11:19 AM
 
Location: Toronto
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Quote:
Originally Posted by ColdCanadian View Post
I don't expect UV does anything to skin in the short term, unless it's causing mild damage. (which most bodies can repair)
Perhaps someone with skin "dark as coal" spends 10-20 minutes outside at UV of 18 and feels no noticeable temp difference due to UV.
It probably wouldn't make sense to describe the heat from UV as "searing" to them.
But then again, in terms of immediate effect, perhaps having darker skin would feel warmer when exposed to sunlight due to the absorption?
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Old 01-17-2011, 11:20 AM
 
Location: Perth, Western Australia
9,598 posts, read 15,613,823 times
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Quote:
Originally Posted by Stumbler. View Post
But then again, in terms of immediate effect, having darker skin would feel warmer when exposed to sunlight due to the absorption?
But that would be the effect of IR, not UV.

Fluorescent bulbs also give off UV, and they don't make anybody warmer.
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Old 01-17-2011, 12:42 PM
 
Location: motueka nz
504 posts, read 488,861 times
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Quote:
Originally Posted by ChesterNZ View Post
I don't think UV is what makes the sun feel hot. The heating part of the sun is due to infra-red radiation. But obviously a high sun angle leads to higher IR and UV, so there ought to be a strong correlation. A better measure of the sun's strength is the insolation per unit area (e.g., Watts per square meter). I'm not aware of a formula for apparent temperature that incorporates the effect of solar insolation but I would be interested in this if such a formula exists.

I know the highlands of northern Queensland can get very high UV indices. Similar climates in Africa and South America could well be some of the most oppressive on earth in summer. But I don't think anything can beat Dallol or the Persian Gulf coast.
Would the conditions that allow for a high UV(other than sun angle) also mean a higher IR?. I'm trying to figure out why the rocks were so hot at such a modest temperature(24C). The previous day was hotter (29C) with a similar dewpoint but a UV of only 12 and the rocks were cool. Both days were sunny with very little wind.
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