We arrived in Stonehaven on the day of one of the biggest storms of the year - the one that obliterated various walking routes in the Cairngorms. We found the plaque on the wall of the old town hall down by the harbour. I love the idea of a public barometer, though there was no evidence of it. The storms that lash Britain are the result of areas of low pressure in the atmosphere. So it wouldn't be good to go out to sea in low pressure, unless you had to. Hence the need for a fishing port to have a public barometer in the days before satellite weather forecasts, I looked up how low pressure areas form in the atmosphere. In some places like deserts it is because extra thermal energy from the Sun causes the air to expand, become less dense and rise, In other places, it is said to be due to the divergence of winds. In other words, streams of air from the same place end up going in different directions. This pulls the air in that place apart. Fewer molecules left behind means fewer collisions and so less pressure. My research on the Internet suggests that it happens because of shear forces caused by the rotation of the Earth. Shear forces are tearing forces. The spin of the Earth causes tear on the air. It all has to spin at the same rotational speed but that means the air nearer the poles will have a lower linear speed. I need to relearn Coriolis forces and find out more about Rossby waves to get a full understanding of all this.
But it was ironic that there was a yacht called Pascal in the harbour given the unites for pressure ...
