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Meteorology and Units of Measurement

Meteorology and Units of Measurement. The great quandary…. Why a quandary?. We know we should be purely metric, but both the culture of Meteorology and the public we serve require that we be bi-unital (is that a word?)

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Meteorology and Units of Measurement

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  1. Meteorology and Units of Measurement The great quandary…

  2. Why a quandary? • We know we should be purely metric, but both the culture of Meteorology and the public we serve require that we be bi-unital (is that a word?) • Example: The Fahrenheit is a metric system of human experience – it will not go away anytime soon. • 0 to 100 F is the rough scale of “normal” weather for most Americans. Anything either side is considered way outside of the ordinary. • What’s so wrong with millibars? If it was good enough for the Bjerknes, shouldn’t it be good enough today?

  3. The big one… Temperature • A meteorologist really has to have a feel for both. Anything scientific you read will be in Celsius, most forecasts will be in F. • The dreaded formulae: • To convert degrees Fahrenheit to degrees Celsius: Subtract 32 degrees from Fahrenheit, then divide by 1.8 (aka 9/5) • To convert degrees Celsius to degrees Fahrenheit: Multiply Celsius by 1.8, then add 32 degrees • To convert degrees Celsius to Kelvins (K): Add 273 to Celsius temperature, as K = Degrees Celsius + 273

  4. Temperature, Cont. • My suggestion – learn a few equivalents so you can have a rough idea of Celsius temps: • Besides the obvious (32F = 0 C) • Necessary condition for tropical cyclone development (79F = 26C or 80F =26.5) • Comfort Ranges:

  5. Wind – the 3 headed monster • We drive in mph, and the public likes wind in mph. • Operationally, Meteorologists talk knots because of mariners and pilots. • We read science in m/s . • Hints: • Knots are nautical miles per hour. A nautical mile is 2000 yards, while a statute mile is 1680 yards. So a knot is a little bigger than an mph. Add 15 percent or multiply knot by 1.15 to get mph. Multiply mph by .87 to get knots. • A m/s is about twice as big as a knot: • 10 m/s is about 20 knots (more precisely, 19.44) • Rarely see kph for wind, thankfully

  6. Length • Even the metrics have a problem here – in any field the metric units which give the item of interest a 1 or 2 digit character tend to dominate. • Hints: • Get a feel for a cm. Takes about two and half of them for an inch. • A meter is a little bigger than a yard or 3 feet. • 1m is 39.4 inches • A kilometer is quite a bit smaller than a mile, takes 1.6 of them.

  7. Pressure • Inches of Mercury – What’s that all about? • Very physical and first principles • “Standard” pressure: • 29.92 inches • 1013.2 mb • Commit both to memory • A hecto-Pascal (hPa) is a mb. Also is 100 Pa. • I hate hPa. Don’t you? • BTHOhPa • Blaise was a good friend of mine… • Not Really

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