h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Had a vigourous debate with fellow teacher trainee yesterday about how warm the temperature was possible to be near the summit of a mountain in Switzerland during march.

Basically it boiled down to her personal knowledge of Switzerland in March being that although there was snow on the ground this reflected the sunlight and was capable of giving sunburn. She maintained that the temperature was warm 'because it was more exposed to the sun' and she commented that this contrast surprised most people Snow on the ground but reasonably warm.

I don't necessarily disagree about the bit about sunburn since reflecting sunlight is one of the reasons we are told glaciers, aid and abet climate change and regulation) However, where I departed from her explanation was I had always thought that the sun heated the ground which then radiated that heat to the air above it, which is why air temperature reduces so swiftly as altitude increases, which is why water vapour condenses on mountains and falls as snow, and why cloudless nights are cooler than cloudy ones and you get onshore/offshore breezes during the day and night time cycle. So I said as much: the critical factor of air temperature that was the deciding factor on warmth felt up a mountain not 'being closer to the sun.'

Sticking to my guns as I was, she befuddled me successfully by then asking about shade and why if air temperature is the crucial thing it was cooler in the shade and warmer 'in the sun' and my sense of being correct evaporated.

I feel I'm skirting around the truth somewhat and missing the bigger picture and will gladly await correction if I have made an error but basically who is right me or her?

Well there would be several different factors which determine this. Though I don´t think being closer to the sun has any real effect. Since the sunlight is close to parallell, a few kilometers of distance shouldn´t matter. The fact that you get sunburned has more to do with you recieving not only light from the sun, but light reflected off the ice around you. That and there being more UV-light at higher altitudes as the air is thinner.
If you have snow, you would expect it to be cold. However due to the reflectivity of the snow, there can be a lot of sunlight without the snow warming very much and so not melting. I do believe the thinning of the atmosphere is what matters most, as it is then not able to transfer as much heat to you. But you recieve heat from both the air and from the sunlight, which is why it will be slightly colder in the shadow as one of the heat sources is taken away.

In Ireland, where there is no snow to reflect the sunlight, it is colder on the tops of mountains, so I would say that this is an effect of altitude, and the higher you go, the colder it gets. But I don't know why this is the case, so it is hard to argue for or against your friend's argument.

Might thinner air not mean that the air has less effect on the temperature you feel, since its bumping into you less frequently?

Or is the different too small for that to be a factor?

Traveller in Time on top of the Alps in Februari once every five years
"I think there is a huge difference in air temperature and sense temperature due o radiation.

In the shade there is no radiation to give you the sense of heat, only the air is available to 'heat' you. The air temperatue will be close to or just below zero degrees as there is snow. The air ventilates through the snow and the air temperature will only get as high as the temperature of the snow.

On a sunny spot (preferrably also no wind) you can sun bathe while the radiation of the sun and the reflection of the radiation by the snow provide enogh heat. even more as the radiation is less blocked by the air. The air blocking the radiation is also the clue for why lower altitudes are warmer, higher density enables the air to collect heat as well as the ground heating up the air. "

yes bbitm
Air density is the major factor.There is a zone in the upper atmosphere called the thermosphere where (as the name suggests) it is officially hot because the particles present are highly energised.
However there are so few of them (in a near vacuum) that you would find it distinctly chilly
glen

Thanks you one and all.

I just know i am going to sound thick asking this but , does this mean that sunburn is independant of tempreture ?

best fishes....tod

I think so, it's exposure to radiation (UV I think) which is what affects the skin, hence suntan beds and those photos that show skin damage.

While hillwalking in the Pyrenees, my family and I were pulling handfuls of snow from the ground and stuffing them into our hats to keep cool.

TRiG.