The many pressures of my job
I’ve been talking about low pressure systems a lot these days.
Earlier this month there was Hurricane Michael, followed by last week’s weather bomb, and now all eyes are on a powerful fall storm barrelling up the U.S. coast. The one thing all these systems have in common is a very low pressure at their core.
Air pressure is measured with a barometer. The unit used can be millibars kilopascals or inches of mercury, depending on where you live and what instrument you’re using.
That brings me to a letter I received from Richard Buggeln. Richard lives in Lower Three Fathom Harbour, N.S. – down the Eastern Shore – handy to the sea and about eight feet above sea level.
Last winter, as a weather bomb tracked offshore, he recorded the hourly drop in barometric pressure on his very old Testrite barometer; Richard tells me it’s probably pre-Second World War German!
After the storm had passed, Richard compared his readings to the official pressure readings from Environment Canada, and low and behold, they were within 0.01 inches of mercury of corrected readings from the closest weather station along the shore at Osborne Head, N.S.
Mr. Buggeln wants to know how to convert inches of mercury to millibars.
Not sure if there’s an “app for that” but there is a formula: y = (29.92 x) / 1013.25.
Here, “x” equals the current measurement in millibars and “y” equals the equivalent measurement in inches of mercury.
The average air pressure at sea level is 29.92 inches of mercury, or 1,013.25 millibars.
It’s much easier to go back and forth from kilopascals to millibars: one Kilopascal (kpa) is equal to 10 millibars
(mb).
I’m so glad Mr. Buggeln asked and was kind enough to send a photo of the lovely old instrument.