Tuesday, 31 May 2011

Waterspout off the southeast coast of Australia

When I first started writing this blog, I didn't really know how to write it and one of the suggestions made by one of the Geography Teachers was to watch the news and then write about that news story/footage in more detail. So, I thought I would give it a try..............
This footage was shot yesterday and was shown live on an Australian news channel. According to the reporter the scientific reason for the occurence of a waterspout is when there is a "bit of wind going around in circle" but I think there is slightly more to it than that.......

So, what excatly is a waterspout? Waterspouts are intense vortex funnels, which can sometimes be destructive, with a small width, that occur over water. Like dust devils and tornadoes, waterspouts are convective vortices whose circulations are driven by convection forming rising shafts of air. Proper waterspouts form over the water and will dissipate almost immediately upon touching any landmass. You can also get Tornadic waterspouts which are tornadoes which have been produced by severe thunderstorms and touch down onto or cross a body of water.

This is a cumulus congestus cloud. They are heap clouds which
 have a large vertical and horizontal extent which are often said to look
 like a cauliflower as they have a flat bottom with a rounded but distinct top.
Waterspouts develop beneath the lines of rapidly growing, shallow cumulus congestus clouds (normally around 3000-4000m deep and 600m above the surface).  Most form in very warm subtropical waters, although some can form in large lakes and along the coastline. The vital condition for their formation is a much warmer surface water temperature then the air above. Therefore they form most during summer in subtropical waters or during late summer in lakes and along the northern coastline. A waterspout develops when a shaft of warm air forms at the water surface and begins to rise rapidly, which makes it spin. The waterspout funnel then begins to develop at the surface of the water and then builds up towards the sky. It often looks as if the waterspouts are sucking water up, from the water surface, but it is actually the condensing of water vapour in the rotating vortex and this makes the waterspouts visible. Waterspouts can spin clockwise or anti-clockwise and at the base of the funnel, the water is stirred into mushroom shaped water sprays.

It is easiest to understand them by looking at a diagram:

1. Water temperatures have to be around 26/27 degrees Celcius
2. Rapidly rising warm air forms lines of towering cumulus clouds
3. Rotation, either clockwise or anit-clockwise, begins as air converges on the column of rising air
4. A dark spot, which is normally only visible from above, appears on the ater surface. This is the first sign of a waterspout developing
5. Surface winds of around 50mph can produce sea spray at the base of the waterspout

 Compared to tornadoes, waterspouts are less destructive as they are less well defined. They can pose a threat to infrastucture just off the shoreline or boats, as they have the power to overturn them, but, because they are slow moving and highly visible, boats are normally able to steer away from them and so any possible danger.

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