jueves, agosto 05, 2004

at the speed of rain

Rather than dumping my thoughts here (in order not to bother my friends with permanent odd outbursts) I keep checking the referrers and see what brought people here. The last (of still very, very few) came from google and was a search for goutes - drops. So I thought I might tell you about the internal pressure of droplets which increases with decreasing radius. The reason is that the drop surface is like a skin of water which tries to contract. If the drop is comparably big the resulting forces are like in a plane and have only a small component towards the centre. Small drops in contrast have a stronger curvature of that skin and the resulting forces towards the centre are stronger. They can be that strong that very small drops cannot form because the pressure inside would evaporate them right away. This is why air can be supersaturated with water vapour and no mist forms. Why does it rain then anyway? - Because the air is dirty! The very first and smallest droplets in a newborn cloud form around condensation nuclei which can be any small particle in the air. So the drop forms around that and thus skips the phase of a mini-baby-drop bound to evaporate. And what happens next? You can read that here and do a comparative study between primary science literature (there) and somebody actually explaining things to you (my attempt here).
And - if I want more rain, can't I just make the air dirtier, you may ask? It has been tried, and you can read more about that here. It has been done to an extend that people start worrying about potential environmental implications resulting from the substances used for this cloud seeding. Let alone the political implications of tampering with the weather, possibly somebody else's. Political? Well, yes, in a Clausewitz sense ("War is the continuation of politics by other means").