Eesh. After UThink upgraded the site's software the comment spam problem went away for a while, but it's clawing its way back. For now it's easy enough to use the new junking feature to dump a spam or two per day, but that's already up from one or two per week earlier this month. Hopefully this isn't indicative of the future growth rate.
First really chilly weekend in a while is coming up, and this morning it felt that way. Thought I'd share.
Downtown Minneapolis as seen from across the Mississippi on the East Bank campus. You can always tell when the temperature is comfortably below freezing because the exhaust from the heating systems of the city becomes strikingly visible. I think this is because it's now cold enough for ice grains to condense from the moist outflow before the water vapor can dissapate. 2006:02:15 09:10:42
Really strikingly visible. Especially at sunrise. This is the power plant on the river by my house. 2006:02:15 08:34:16
[Update from the comments]: Dean Armstrong points out that these clouds actually are liquid droplets, not ice crystals. Doh!
With that in mind, now I know why the condensation clouds are so visible on cold mornings, and it's exactly the same process that makes your breath visible. Remember from weather reports that low dewpoint and low humidity are the same thing, meaning that cold air can carry less dissolved water vapor. If you take warm humid air and cool it down to its dewpoint it becomes super-saturated, the water spontaneously condenses out as droplets, and a fog forms.
When warm, moist building exhaust (or your breath) hits the outside air, the two begin to mix. The mixture cools, but the water vapor is also being diluted, lowering the dewpoint. So it's a race. If the temperature difference is large, the hot air doesn't have to mix with very much cold air to cool down a lot, and the temperature can catch up to the dewpoint on the way down. But eventually ambient conditions dominate, since there's a lot of air outside after all, the dewpoint falls back below the temperature, and the tiny droplets evaporate.
So on a really cold morning, the temperature difference is huge (by tingly fingers standards, anyway, writes the guy sitting in the lab full of cryogens), the temperature gets down to the dewpoint quickly and stays there for a while. Meaning thick fluffy clouds that hang around for a bit and stand out in the sunrise.