Rain does a good job of washing away nature's dirt, but did you know rain can't exist without it?
Raindrops need some sort of particle to form -- officially known in the weather world as "cloud condensation nuclei" or "CCN". It's the dust, smoke and other tiny particles in the atmosphere that provide the basis for water vapor to cling to and form a raindrop.
I was recently alerted to a clip on YouTube that shows just how important this CCN.
This video was taken on board the ice breaker "Oden" during the "Arctic Summer Clouds Ocean Study" (ASCOS) 2008 expedition to the Arctic.
According to the video, the temperature outside was -8C (or about 18 degrees F) and the cloud condensation nuclei concentration was about 100 times less than in the lower latitudes.
The research team set out a cup of hot tea, but noticed that there was not much steam coming off the cup. But put a lighter there, and watch as the smoke particles from the flame all of a sudden provide the nuclei needed to create the steam.
My questions to the crew: "What, no coffee?" and "18 degrees outside and the crew is in short sleeves?" They must keep the heater on high inside the vessel :)