Wednesday, November 14, 2007

Sudden Fogs

kw: nucleation

I've had two experiences of a similar phenomenon. The more recent occurred at 6:11 this morning. I'd just heard on the radio that there was heavy fog in the area. Before going out to get the morning paper, I looked through glass storm door, and clearly saw the streetlight across the way.

I stepped out the door, and exhaled a foggy breath. That tiny cloud spread quickly, and by the time I got to the driveway, the same streetlight was indistinct in a foggy gloom. It thickened a little more as I returned to the house.

The air had cooled slowly and was in a metastable state, with humidity over 100%, "supercooled." I happened to supply the trigger.

Thirty years ago, living in Anaheim, I took my usual (for then) morning shower, noting the clear sky through the window. After the shower, I opened the window to let the steam clear, and saw fog spread through the neighborhood in seconds, resulting in a real pea-souper (P.S. These days, I bathe at night, preferring to sleep clean).

I feel privileged to have witnessed supercooling and sudden condensation on a scale larger than a test tube.

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