February 25th 09, 09:13 AM
posted to uk.sci.weather
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First recorded activity by Weather-Banter: Dec 2003
Posts: 2,744
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Sharp point in isobar
Yokel wrote:
Those pointy isobars are where there is a "col" forecast with a pressure at
the "saddle" only just below the value of the isobar concerned. If the
forecast pressure had been a touch lower, the isobars would have swept
smoothly round the anticyclones either side as you would have expected. If
the forecast pressure had been a touch higher, the isobars would have
"joined" to continue above and below the "col". There has to be a point at
which a particular isobar changes from one configuration to the other as the
pressure at the centre of the "col" changes, and this just happened to be
it.
Sometimes on animations you can actually see this happen and the isobars
"snap" from one configuration to the other as the pressure changes.
A similar effect can be seen on the "streamline" charts used to analyse
tropical weather, where pressure changes are very small except in tropical
storms so isobaric analysis is not very illuminating. A surprisingly common
feature is four streamlines, two meeting head on at a point and two flowing
away it, while the streamlines either side swing away from the "meeting"
ones to turn parallel to the "diverging" ones.
Thank you for that explanation.
Hugh
--
Hugh Newbury
www.evershot-weather.org
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