Friday, January 21, 2011
Last Monday it was so warm that it rained, but now it's turned cold again and we're not expected to reach 20° over the weekend. So here's some cold weather fun.
Geysers are at their best on a cold winter's day, when the hot water turns into volleys of little ice rockets, each at the end of its personal vapor trail, as you see above. It's a simple matter of surface area:mass ratio -- lots of little drops will freeze or evaporate faster than one large body of water because more surface is exposed to the air. It happens so fast that most of the water evaporates and the remainder freezes before it can ever hit the ground.
I don't understand why hot water evaporates quicker in cold air than warm air. You'd think it would be easy to discover, what with this awesome new intertubes thingy, but no. I haven't found anyone who explains it directly. So here's my best guess: since transitioning between water and vapor requires energy, evaporation happens easier when more energy is transferring between the water and the air, which happens faster when there's a greater difference between water and air temperature. So T(water) - T(air) = k*Evaporation rate.
That might be totally wrong. Maybe it's all about the humidity. We all know that cold air is drier than warm air, so maybe that's the major reason why the geyser basins so fill up with steam on colder days - because the air is drier, not because it's colder. That's certainly a factor, but I'd be surprised if it's a large one.
I posted this photo is a response to this great video which is getting a lot of attention this week. Yellowknife is only 4° south of the Arctic Circle and they expect a high of -27° F. today, which is quite a bit colder than it was the day I took my photo above. The evaporation is wickedly dramatic:
Not even a hat or gloves. Now that's a Canadian.
Video via Daily Dish