Science desk
< January 25	<< Dec \| January \| Feb >>	January 27 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is a transcluded archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 26[edit]

What's the mean or median air pressure at the Empire State Building observatory?[edit]

The International Standard Atmosphere gives an answer but also gives average sea level 101325 pascals and 59.0F when the weather station's roughly 101750 pascals corrected to sea level and 56.?F plus 0.499F environmental lapse rate (6.5C/km) from 0 feet to 140. Should its pressure for 1106' above sea level (nostril height) be increased by 101750/101325? Sagittarian Milky Way (talk) 03:20, 26 January 2024 (UTC)[reply]

Multiplying the pressure from the standard atmosphere at that altitude with 101750/101325 takes care of the non-standard sealevel pressure. That's a 4‰ (note: per mille) increase in pressure. The lower than standard temperature increases the pressure lapse rate by about 5‰, so that lowers the pressure at the observatory by 5‰ of the difference between there and sea level. That's a smaller correction. A non-standard humidity also affects the lapse rate: higher humidity gives a lower lapse rate. If the top of the building is in the clouds, pressure lapse rate is increased. When some of the water vapour in the air condenses, the volume decreases and density increases. The pressure lapse rate is simply the density of the air divided by gravity. Both temperature and humidity vary from day to day. To be really sure, you'll have to measure it. PiusImpavidus (talk) 08:52, 26 January 2024 (UTC)[reply]

I forgot to think of that (denser column should thin faster). Why is ISA humidity zero at all altitudes, shouldn't they have at least a simple function fitted to the avg humidity of each altitude? Do you know where NOAA or National Climate Data Center or NWS or whoever gives its pressure averages? ~1017.5 from a (old?) El Dorado Weather map but ~1017.0 from a different map of known averaging period 1981-2010. I found current maps 1991-2020 but only even integers weird un-interpolatable shape.Sagittarian Milky Way (talk) 20:59, 26 January 2024 (UTC)[reply]

I don't know why the ISA is the way it is. I suppose temperature and humidity are so variable that choosing a more realistic standard value doesn't give a significant improvement. With humidity set to zero, you don't have to deal with cloud formation.

On the website of my national meteorological institute I can simply download all validated hourly air pressure readings of all weather stations in my country since 1900. Is there no such option in the US? PiusImpavidus (talk) 14:32, 27 January 2024 (UTC)[reply]

30-year average pressure is harder to find than most other things (even pressure for a specific hour decades ago). Sagittarian Milky Way (talk) 05:07, 28 January 2024 (UTC)[reply]

Yes, it may not be listed because no-one (until you, now) may have wanted to know it. You might just have to download all the individual values and work out the averages yourself. {The poster formerly known as 87.81.230.195} 90.205.103.187 (talk) 19:50, 28 January 2024 (UTC)[reply]

It safe trust me its breathible. 23.24.81.162 (talk) 22:10, 1 February 2024 (UTC)[reply]