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Glom
2003-May-29, 02:45 PM
In the polar regions, is there much cloud cover? I would have thought that since it's too cold for evaporation, there would be no cloud formation nearby and any clouds forming near the tropics would have already disposed of their water before getting to the poles. With the white surface then, good sunglasses are a must. Would you need UV protection? Since the sunlight is travelling through a much greater thickness of air, I would have thought most UV light would be absorbed.

snowcelt
2003-May-29, 03:19 PM
Sounds like you are talking about summertime. In the 'summertime', when the light is a 24hr a day reality; and you are on a bright , reflective surface: sunglasses or a slit-view eye pieces would be a good idea (by the way, temp can be -15C, yet you can wear a t-shirt and sweat...if you are working!) When is the last time you saw a pale Inuit? As for cloud cover: summer is very clear (sometimes). But, as in any place in the world , water vapour is a reality. Evaporation? In the artic, sublimation creates much of the cloud formation. As for UV, have you not ever heard of O3 zone? In the artic, the ozone layer at some times is so thin that UV is a more problemtic then in the sahara!

MAPNUT
2003-May-29, 03:22 PM
I think you're right although I don't have facts at my fingertips. I've heard it said that it only snows about 1" a year at the South Pole so presumably it's seldom cloudy. Must be fantastic stargazing in winter, if you can keep your gear from frosting over! I've also heard that the Arctic is very dry due to the lack of open water. I remember reading that if anything caused the Arctic Ocean's ice cover to melt, there would then be tremendous snowfall on the northern lands because of the increased evaporation, and an ice age could actually begin because glaciers would form.

g99
2003-May-29, 06:12 PM
The reason for the lack of clouds and rain is more because of the temp. The colder it is, the less water a single packet of air can hold. that is why you get condensation. Hot humid air has alot of water in it. If you cool that any amount it is pysically incapable of holding all that water and it looses some. This relased water either falls as rain or condenses to clouds. Usually both. So if it is too cold for the air to hold much water, don't expect much more than a wisp of clouds.

ex. At -15 deg celcius the density of the water vapor in the air is ~1.7 g/m^3. In contrast, in 20 deg Celcius air there is ~17 g/m^3. (Oliver, John E. "Climatology: An Atmospheric Science")

ToSeek
2003-May-29, 09:41 PM
The reason for the lack of clouds and rain is more because of the temp. The colder it is, the less water a single packet of air can hold. that is why you get condensation. Hot humid air has alot of water in it. If you cool that any amount it is pysically incapable of holding all that water and it looses some. This relased water either falls as rain or condenses to clouds. Usually both. So if it is too cold for the air to hold much water, don't expect much more than a wisp of clouds.

ex. At -15 deg celcius the density of the water vapor in the air is ~1.7 g/m^3. In contrast, in 20 deg Celcius air there is ~17 g/m^3. (Oliver, John E. "Climatology: An Atmospheric Science")

The notion that cold air can hold less water vapor than warm air is Bad Meteorology. (http://www.ems.psu.edu/~fraser/Bad/BadClouds.html)

g99
2003-May-29, 10:40 PM
Very interesting ToSeek. My climatology professor basically said what i said. The explanation given by your link makes sense.

[upon furtter reading of the chapter in the book:] Ahhhh! here it is! This author does say this exactly. Dew point depends on the condensation/evaporation rate [paraphrasing]. So he does mention it, I just skimmed over it. Hmmm....Very interesting. So i had the basics right, but for the wrong reason. Thanks. This makes much more sense than previously.

added: so with the minimal sublimation and incoming water vapor to the poles, it make sense for the lack of coulds.

I could not find it. But does anyone know the current sublimation/evaporation rate in the poles? is it greater or less than years previously? (i have found info on Martian sublimation, but not the earth's)

kilopi
2003-May-29, 11:48 PM
The notion that cold air can hold less water vapor than warm air is Bad Meteorology. (http://www.ems.psu.edu/~fraser/Bad/BadClouds.html)
You have to be careful with the Bad Meteorology pages. Even though they were the inspiration for the BA pages, the BM tends to go a bit overboard. For instance, in the Bad Cloud FAQ (http://www.ems.psu.edu/~fraser/Bad/BadFAQ/BadCloudsFAQ.html), he says "When I was in grade school, I was taught that water freezes if its temperature is below 32 F and evaporates if it is above 212 F. Between those temperatures, it remains a liquid. This was all patent nonsense." So, basically, he's saying that teaching 8 year-olds that water freezes at 32 F is nonsense.

He has his reasons for saying that, but I would be a little more forgiving than him!

The vapor pressure of water at cold temperatures is much smaller than the vapor pressure of water at hot temperatures. It doesn't matter how much other air is present, or what type of air is present--that's his point. It's not the air that is important, it is the vapor pressure. There can be more water in vapor form at hot temperature than at cold temperature. I agree with him that that is a better way of saying it than "hot air holds more water than cold air", but I wouldn't go so far as to call it nonsense. Wrong maybe, but not nonsense.

Why? Well, look at his answer to one of the other FAQ questions (I know, I know):
I donít object to simplifications. However, you must make a distinction between something which has been made simple (stripped to its essence), and something which has been made simplistic (stripped of its essence). The explanation which attributes the formation of clouds to the inability of the air to hold as much water vapor at lower temperatures is not a simplification, it is categorically wrong!

See, using the same logic, he would say that newtonian mechanics is categorically wrong--no matter how successful it is. But that doesn't make newtonian mechanics nonsense.

Beaver
2003-May-30, 12:18 AM
When I was in grade school, I was taught that water freezes if its temperature is below 32 F and evaporates if it is above 212 F. Between those temperatures, it remains a liquid. This was all patent nonsense." So, basically, he's saying that teaching 8 year-olds that water freezes at 32 F is nonsense.

He has his reasons for saying that, but I would be a little more forgiving than him!


I agree with you very much so, I think he has become very educated over the years and has fogotten what a eight year old can absorb and comprehend.

tracer
2003-May-30, 12:58 AM
I've heard it said that it only snows about 1" a year at the South Pole
What you probably heard was that it actually snows a couple of feet per year, but that this represents only as much water as a rainfall of 1-4 inches per year.

(At least, that's what they said on this week's Nova rerun.)

g99
2003-May-30, 01:52 AM
I don't have a problem with teaching kids that making air cold means more rain and clouds than making air warmer. Its simplified and will make much more sense to a 10 year old than saying "The pressure differences of water vapor and the temperature are related. You see little billy that if the condensation rate is higher than the evaporation rate you get clouds. But if the evaporation rate is higher thaan the condensation rate, then you get clear skies...." I know kids are smart, but leave something for university professors. :-)

dgruss23
2003-May-30, 02:47 AM
kilopi wrote: See, using the same logic, he would say that newtonian mechanics is categorically wrong--no matter how successful it is. But that doesn't make newtonian mechanics nonsense.

Hey, wouldn't JS say that to say newtonian mechanics is wrong is nonsense? So to say that newtonian mechanics is nonsense because it is wrong would be nonsense squared (at least to some)?

Kizarvexis
2003-May-30, 04:00 AM
Sounds like you are talking about summertime. In the 'summertime', when the light is a 24hr a day reality; and you are on a bright , reflective surface: sunglasses or a slit-view eye pieces would be a good idea (by the way, temp can be -15C, yet you can wear a t-shirt and sweat...if you are working!) When is the last time you saw a pale Inuit? As for cloud cover: summer is very clear (sometimes). But, as in any place in the world , water vapour is a reality. Evaporation? In the artic, sublimation creates much of the cloud formation. As for UV, have you not ever heard of O3 zone? In the artic, the ozone layer at some times is so thin that UV is a more problemtic then in the sahara!

As I understand it, Inuits are not pale, because they don't need to manufacture as much vitamin D as they get enough from their diet.

I was watching a show on race and why it is a meaningless concept. (DNA wise there is no difference between the various races according to this show.) Anyways, they were discussing why we are different colors. Evidently, it is because of UV absorption to make vitamin D. People in the lower lattitudes get a lot of sun, so they don't need to be as pale to absorb enough UV to make vitamin D. The higher lattitudes need to be paler to absorb enough UV to make vitamin D with the lesser amount of sunlight. Evidently, the Inuits get enough vitamin D from their diet that they don't need to be as pale as others who are that far north.

Kizarvexis

Colt
2003-May-30, 04:53 AM
You can get a snowtan up here. Most people wear their sunglasses more in winter than in summer. Not sure what else to add.. And yes, it can get hot if you are outside doing even simple things when the sun is out and it is clear. -Colt

kilopi
2003-May-30, 10:51 AM
Hey, wouldn't JS say that to say newtonian mechanics is wrong is nonsense? So to say that newtonian mechanics is nonsense because it is wrong would be nonsense squared (at least to some)?
Heh, that's pretty good. But, not to speak for JS, but I think he'd probably be more direct than that. :)

Water content in snow (http://geoimages.berkeley.edu/GeoImages/Powell/Afghan/065.html) can vary, of course (http://ulysses.atmos.colostate.edu/~odie/snowtxt.html#Facts), so precipitation (rain or the melted water content of snow) is usually the catchall term, idnit?