NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Waterspouts.
From: George Huxtable
Date: 2003 Sep 17, 18:22 +0100
From: George Huxtable
Date: 2003 Sep 17, 18:22 +0100
Waterspouts. At a recent meeting of our local cruising club (information about that club can be found on) there was interest in reports of recent sightings of waterspouts, on two successive days off the North Brittany coast, by Nav-L member Clive Sutherland. It turned out that several other members had observed waterspouts, in European coastal waters, at different times, so these phenomena are not particularly rare. None were close-quarters encounters, perhaps fortunately so. Me, I've never been aware of one, glad to say. There was general agreement that (from a distance, anyway) these appeared to be undramatic, without any menacing roar, and rather stable, lasting for 20 to 30 minutes, travelling slowly without significant change. Weather conditions in the vicinity were usually light winds and heavy overcast low cloud. Nobody was brave (or foolhardy) enough to head towards the spout for a closer look. It was hard to be sure how wide these spouts were and how far away, but some estimates were of "a couple of boat-lengths" across (perhaps 20 metres) with disturbed sea surface over that diameter and a grey column of about that diameter, with a sharply defined edge, rising from the surface, and then slanting away, at sometimes a shallow angle, to disappear into the cloud base. Other waterspouts were reckoned to be much bigger, perhaps hundreds of meters across. These raise a few question. Have mariners, (perhaps Nav-L members, even) in large vessels or small, passed through the eye of a waterspout? What's it like in there? Can sails or rigging survive if not furled in time? Do published accounts exist? Presumably the pressure within the column is significantly less than that of the surroundings. Is it ever low enough to give rise to a noticeable mounding of the water surface below it? The turbulence will make any precise observation rather difficult, to say the least. How does a waterspout function? I have read that both tornados and waterspouts can grow downwards, swirling from the cloud layer above. I think I can understand a tornado, over Sun-heated land, as it takes in hot air from the layer just above the surface, and the rising of that hot air within the column that provides the energy to drive it. It's the dust and debris drawn from the ground that darkens the air-column to make it so visible. Is that acceptable as a plausible model? How does that work for a waterspout, however? Presumably, the dark column is visible because it carries a load of water or spray, drawn up from the surface. But once the column has grown downwards to reach the water surface, surely the effect of any water and spray that it picks up will be to quench and cool the column of air: just the opposite to a land tornado. In the summer the sea temperature will surely always be much cooler than the air above it, and any evaporation will cool the column further still. Is there any published study of how all this works? Do list members have any explanations of their own? George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================