Thank you for that, which is illuminating.
The core of my speculation was slightly different, though. What I suspect is that treating the increase in wind speed due to increased water temperature in isolation may be misleading. The paper whose abstract was posted here did not go into details of what was done in this regard. It may be that you can show that increasing sea temperature by 2 degrees can give you no more than a 5% increase in wind speed in normal conditions. But if the preconditions for a very severe storm are abnormal, and one of a combination of factors required is high sea temperature, then increasing the sea temperature on a permanent basis could make the preconditions of very severe cyclone development much more common than hitherto.
I would welcome any comment on this.
Roger Musson
> -----Original Message-----
> From: Natural hazards and disasters
> [mailto:[log in to unmask]]On Behalf Of Palmer,
> Steve
> Sent: 02 September 2005 14:48
> To: [log in to unmask]
> Subject: Re: HURRICANES AND GLOBAL WARMING
>
>
> Roger Musson wrote:
> "The paper quotes some other studies that model a projected
> increase in
> wind speed in a cyclone of only a few percent, given a rise in sea
> temperature of a few degrees, and anyone can appreciate that
> if you have
> a cyclone with wind speeds of 100 mph, it won't be that much worse if
> they increase to 105 mph."
>
> Technical point - wind pressure is the square of the speed, so a 5%
> increase in speed leads to a 10% increase in pressure. 10% may well be
> significant for a structure that is near its design limit.
>
> See the entry on "wind pressure" in the AMS Glossary of
> Meteorology. The
> formula is
> p = 1/2 (1+c).rho.v**2
> Where p is pressure, rho is density, v is velocity normal to the
> surface. c is a structure constant which depends on the shape of the
> surface. For a large flat plate c is about 1 which indicates that the
> pressure on the plate is the sum of the wind load on the facing side
> plus an equal suction on the lee side.
>
> In terms of damage to buildings, the suction is often more destructive
> than the load, since it is relatively easy to construct a
> roof or window
> to withstand the direct pressure, but much more difficult to
> stop roofs
> lifting or windows being sucked out of their frames. This is
> particularly a problem with shallow-pitched roofs where the lee side
> acts like an aerofoil.
>
> For a cylinder, c is about -0.3, but then other factors operate,
> particularly resonance because a cylinder will shed vortices on
> alternate sides, which is why metal chimneys are often
> constructed with
> a spiral to disrupt the vortex shedding and prevent a destructive
> resonance building up.
>
> Another consequence is that if flying debris breaches the
> windward side
> of a building, the pressure will be transferred through the
> interior and
> double the load on the downwind surfaces. The building may
> then explode.
>
> Hence in any strong wind situation, one of the first preventative
> actions should be to secure any loose debris, old planks,
> roofing sheets
> etc.
>
> Wind, like water flows, is not uniform, it is a turbulence phenomenon
> where peak speeds may be much higher than the mean. Also there will be
> funnelling through other structures, again giving much higher speeds.
>
> Stephen Palmer
> Technical Co-ordination Manager
> Met Office FitzRoy Road Exeter EX1 3PB United Kingdom
> email: [log in to unmask]
> http://www.metoffice.gov.uk
>
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