That's true. The model to 86 km is pretty standard and completely shared with ICAO and ISO although I am not sure they go to the same altitude. Above 86 km, the model gets strange, the gas molecules are mostly ionized, and the molecular weight is far different than the lower atmosphere. I think it is mostly for NASA. You can download the pdf file for the 1976 US Standard Atmosphere from some government site. ISO and ICAO are for-fee standards.
--- On Fri, 12/4/09, John Frewen-Lord <j...@frewston.plus.com> wrote: From: John Frewen-Lord <j...@frewston.plus.com> Subject: Re: [USMA:46251] Re: Simple Metric web site. To: jmsteele9...@sbcglobal.net, "U.S. Metric Association" <usma@colostate.edu> Date: Friday, December 4, 2009, 6:22 PM I do not know the basis of how all this is calibrated, but 1000 km - when talking about standard atmospheres?? THINK about it - 1000 km is way above what close proximity satellites orbit the earth at!!! Not much air up there. Regards JF-L ----- Original Message ----- From: John M. Steele To: U.S. Metric Association Sent: Friday, December 04, 2009 11:02 PM Subject: [USMA:46251] Re: Simple Metric web site. I believe the CGPM just copies it. It actually originates in the US, ICAO, and ISO Standard atmospheres, which define that sea level pressure, temperature (15 °C) and temperature lapse rate. (The lapse rate changes in various segments above 11 km). This leads to the assumptions used in calibration of aircraft altimeters, which really measure pressure but indicate altitude. The US defines a standard atmosphere to 1000 km, ICAO and ISO agree at lower altitudes, but end at a lower altitude as no commercial aircraft flies at 1000 km. --- On Fri, 12/4/09, Bill Hooper <billhoope...@gmail.com> wrote: From: Bill Hooper <billhoope...@gmail.com> Subject: [USMA:46250] Re: Simple Metric web site. To: "U.S. Metric Association" <usma@colostate.edu> Date: Friday, December 4, 2009, 4:51 PM On Dec 4 , at 11:38 AM, Pierre Abbat wrote (in response to my earlier note): (I wrote) Normal or average atmospheric pressure is about 101.3 kPa. (There may be different standards for identifying "normal" or "average" air pressure.) (Pierre replied) 101.325 kPa, to be exact, is the standard. The value of 101.325 kPa is the exact value (the "standard") specified by CGPM for the standard atmospheric pressure, as Pierre correctly points out. That value is as close to a universal value as is possible. In addition, however, there are other circumstances where different standards are used. Here are two I've encountered (from Wikipedia): ... International Union of Pure and Applied Chemistry (IUPAC) recommended that for the purposes of specifying the properties of substances, “the standard pressure” should be defined as precisely 100 kPa ... rather than the 101.325 kPa value of “one standard atmosphere”. ... For natural gas, the petroleum industry uses a standard temperature of 15.6 °C (60.1 °F), pressure 101.56 kPa (14.730 psi). (air pressure) The CGPM standard is probably more precise than is reasonable for many uses, such as reporting air pressure in weather reports. For such measurements, a rounder value of 101.3 kPa or even 101 kPa might be suitable as a state "normal" or "average". Certainly, atmospheric pressure is affected by altitude and other factors. For specific locations or specific special conditions, the CGPM standard atmosphere may not be too close to the actual average of the ambient pressure. This is not meant to be argumentative. I recognize the value of 101.325 kPa as the best value to use for most technical purposes. I just felt it was necessary to indicate in my note that there are different possible averages or normal values that might be used. Regards, Bill Hooper ============================== If you have not already done so, please note my new email address: billhoope...@gmail.com (Old address will still work OK temporarily.)
