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DID YOU KNOW? PART 6

Welcome to the first 'Did You Know' for this week. 'Did You Know' is a daily OCC segment where we tackle some of the easy and not so easy questions we come across on our social networks.


Did You Know:

In Australia if you face the wind, LOW pressure will always be located on your left and HIGH pressure will always be located on your right.


interested? well read on

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This is called Buys Ballot's Law. The Law as you can imagine was named after a Dutch Meteorologist called Christophorus Henricus Diedericus Buys Ballot who first published his finding in 1857. His law was specific for the Northern Hemisphere initially but it didn't take long to deduce that the law worked in the Southern hemisphere as well. The difference is that in the Northern Hemisphere if your back is to the wind, LOW pressure will always be on your left while HIGH pressure will be on your right.


WHY DOES THIS LAW EXIST?

Wind flows from HIGH pressure to LOW pressure known as the Pressure Gradient Force but it doesn't flow directly towards it. Instead the surface friction of the earth and the earth's spin changes the direction of the wind to run roughly parallel to isobars but the centripetal force acting into LOW pressure systems allow those winds to cross isobars. Long story short, air will flow from HIGH to LOW pressure but it will do so at a considerable angle.

WHY IS THIS LAW USEFUL?

1 - In times of cyclonic activity you knew that if the wind was a south-easterly you would likely be in the strongest part of a Tropical Cyclone or Tropical LOW (that left front quadrant). 2 - For graziers and farmers in the mid latitude where a large section of our crop land lies if they were getting northerly winds, they knew the chance of rain and storms was on the way as LOW pressure was coming their way. Because as we discussed on Friday, weather moves from west to east over a large portion of the planet. In the old days this law would be added to the old wives tale ('Red Sky at night, shepherd's delight, red sky in the morning shepherd's warning') This would then increase their confidence of rain on the way in the next 24 hours. 3 - For ships as soon as they felt that northerly/north-westerly wind shift to a southerly they would know a frontal system was passing over them and better weather was likely on the other side.

Check out today's surface winds and pressure chart thanks to windy.com below. There's not much happening but imagine you're a stick figure facing the wind at any location on the map you will notice that LOWER pressure lies left of you, HIGHER pressure lies right of you.



windy.com surface winds mslp chart. Practice using Buys Ballot's Law

Even with the advent of radar, satellite and improvement of computer models when you're on the ground chasing storms along a trough line, the basic knowledge of the physics laws that govern weather is a must, it's much easier to pop out of the car for a sec to use Buys Ballot's law to identify if you've gone too far west of the storm lines that are about to develop than taking out 5 or 6 different radars/models to try and identify this.



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