[USMA:35496] Re: Weather channel web site and millibars

[G Stanley Doore]

Title: Re: [USMA:35476] Re: Weather channel web site and millibars

Pat et al:   The standard atmospheric pressure is  1013.25 hPa or 101.325 kPa or 1013.25 mbar.  That's a total of six digits.   We must differentiate between reporting pressure and observing pressure.  The public doesn't need all six digits, therefore the public is given something less.  The full atmospheric pressure observations go into the forecast models so precision is not lost computationally.  Most obs are now taken by automatic observing equipment in the US.  The public doesn't need that precision, although they can get it via the Internet.   Although there are so many ways to present pressure in the SI as you've indicted, common usage of kPa is preferable for the public to be compatible with uses in other fields.  Using many different SI prefixes will be confusing to the public.   Stan Doore ----- Original Message ----- From: Pat Naughtin To: U.S. Metric Association Sent: Wednesday, December 28, 2005 2:21 PM Subject: [USMA:35491] Re: Weather channel web site and millibars On 28/12/05 12:03 AM, "G Stanley Doore" <[EMAIL PROTECTED]> wrote: Hi Pat et al: I didn't mean to imply that millibars was SI, only that it is metric.  It's used during severe storm situations to avoid misunderstanding and not to confuse the public.  The digits and decimal point placement for millibars are identical to hectopascals in the SI.  Unfortunately, we still get some writers, including The Weather Channel, using millibars. What's needed is an effort to get atmospheric pressure reported in kilopascals so the public easily can relate it to other pressures such tire pressure, radiator pressure, boiler pressure, etc. which are being used more frequently in SI.  I believe tire pressure in kilopascals now is molded onto automotive tires. Stan Doore Dear Stan, The contest between pressure in hectopascals and kilopascals seems to be based on two separate ideas. 1   If meteorologists continue to use hectopascals then they do not need to change their mind set of numbers from millibars to hectopascals. They can refer to old data and use it interchangeably with newer data without any change in their mindset. It’s a sort of soft conversion from metric to SI units but it also means that they will continue to swap around the unit names as if they were equally interchangeable. 2   Meteorologists like the precision of that a number like 1011.4 hectopascals suggests. This type of number (with 5 digits) also allows movements in pressures to be readily observed as to whether they are moving up or down — a critical part of the meteorologist’s art. Has anyone in the meteorology profession canvassed the ideas of decipascals (making our example 10114 dPa without a fraction) or centipascals (101140 cPa ), or even millipascals (1011400 mPa that may be too precise for current instrumentation). Your suggestion — to use kilopascals for air pressure — seems to me to be sound in that it would use one of the preferred prefixes based on 1000s rather than non-preferred hecto. But writing the pressure as 101.14 doesn’t have any additional practical benefit such as getting rid of fractions with their associated errors and confusions. Obviously, rounding this to 101 loses precision and does not allow for subtle pressure changes to be observed and reported. However, to a working meteorologist faced with the dual problems of changing their own personal mindsets and the much harder task of getting their associates to do this at the same time will probably be placed in the too hard basket for some considerable time into the future. I don’t know the solution to this dilemma except to use the standard metrication techniques such as: avoiding conversions altogether, avoiding fractions both vulgar and decimal, arranging for relevant experts to discuss this issue as soon as possible and at length, and setting an M-day to upgrade to the new methods (2010 October 10 = 10/10/10 springs to mind). And only the third and fourth of these seems to me to have any immediate practicality. Cheers, Pat Naughtin LCAMS (USMA), Member NSAA* PO Box 305, Belmont, 3216 Geelong, Australia Phone 61 3 5241 2008 Pat Naughtin is the editor of the free online monthly newsletter, 'Metrication matters'. You can subscribe by going to http://www.metricationmatters.com/newsletter  * Pat is the editor of the 'Numbers and measurement' chapter of the Australian Government Publishing Service 'Style manual – for writers, editors and printers', he is a Lifetime Certified Advanced Metrication Specialist (LCAMS) with the United States Metric Association, a member of the National Speakers Association of Australia and the International Federation for Professional Speakers. For more information go to: http://metricationmatters.com This email and its attachments are for the sole use of the addressee and may contain information that is confidential and/or legally privileged. This email and its attachments are subject to copyright and should not be partly or wholly reproduced without the consent of the copyright owner. Any unauthorised use of disclosure of this email or its attachments is prohibited. 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