Talk:Barometric formula

message: Warning the imperial constants provided seems wrong
jmrog
why give the eq2 since its a special case?  —Preceding unsigned comment added by 85.156.81.72 (talk) 08:28, 1 August 2009 (UTC)
thread_title: Error

message: In the equations, what determines the correct value for b to be used? Given the same height in meters, I get different results depending on b. SharkD (talk) 21:00, 31 August 2009 (UTC)
thread_title:  Choosing values for b 

message: In the table, shouldn't the Standard Temperture for subscript b=0 be 298 Kelvin rather than 288 Kelvin?  298 Kelvin is used in the chemistry as standard room temperature.  —Preceding unsigned comment added by Cougar40 (talk • contribs) 16:48, 16 July 2010 (UTC)
replies: text: I believe that standard temperature, when talking about the atmosphere, is actually 273K. See Daniel Jacob's "Introduction to Atmospheric Chemistry". Sean Egan (talk) 18:48, 24 October 2013 (UTC)
thread_title:  Incorrect Value for Standard Temperature? 

message: Equation 2 is necessary for isothermal regions of the atmosphere, such as the stratosphere starting at a geopotential altitude of 36500 ft.  It is therefore not a special case, and necessary to any full understanding of the regions of earth's atmosphere.  I believe that there are two separate isothermal regions.  
Regarding units:  the kelvin temperature system should not be used with a foot, pound, second unit system, or english units.  The proper temperature system is degree Rankine, which is a temperature system with 0 degrees at absolute zero, and increasing at the same rate as degrees farenheit (1.8 degree Rankine = 1 degree Kelvin).  I suggest a change in the constants used to reflect a realistic system of units, as unsuspecting users will not check this.  
Further, these equations are often used in aerospace settings, where the specific gas constant is used instead of the universal gas constant.  This should be mentioned with a link to the article discussing these two different physical values.  Rspecific = R/M, where R is the universal gas constant and M is the molar mass.  Also, lb-mol is not the same as the SI mole.  — Preceding unsigned comment added by Spcaeguyformertah (talk • contribs) 23:15, 22 January 2011 (UTC)
thread_title: Equations and Units

message: The section, Estimating the Temperature should be removed.  It is completely irrelevant to the article, contains zero references, and its inclusion is simply confusing.173.189.77.96 (talk) 19:43, 13 April 2014 (UTC)
thread_title:  Challenge 

message: I think there is an error in Pressure Equation 1.
see also https://en.wikipedia.org/wiki/Atmospheric_pressure  — Preceding unsigned comment added by Gimusi (talk • contribs) 08:41, 6 December 2015 (UTC)
replies: text: Specifically? I think it's a bit odd myself, but can't quite say why. I can't see how it comes from the derivation later on. --Cedderstk 12:09, 26 August 2018 (UTC)
replies: text: I agree there is a (sign) error in the first equation. In its current form it yields a pressure P at a height h above the reference height h_b with pressure P_b with P > P_b, for a situation where T decreases with height h (as is mostly the case in the troposphere) and where height h is taken positive upwards. I will correct the sign shortly.Redav (talk) 18:01, 29 December 2020 (UTC)
thread_title:  Error in Pressure Equation 1 

message: AFAIK the SI-system has no such unit as a "geometric meter". It doesn't have a "geopotential meter" either.
See #9 and #11 at this page: http://physics.nist.gov/cuu/Units/checklist.html
I therefore suggest that this part:
"There are two different equations for computing density at various height regimes below 86 geometric km"
- is changed to this:
"There are two different equations for computing density at various geometric height regimes below 86 km"
And in this part: "(84 852 geopotential meters or 278,385.8 geopotential feet)"
- "geopotential" should not be placed between the numbers and the units, so that part should be rewritten too.
T.O.K.
— Preceding unsigned comment added by 37.253.241.7 (talk) 00:38, 8 February 2017 (UTC)
thread_title:  Special types of kilometers ? 

message: The two equations don't seem very well sourced. The code at least is tallies with Stull. It just seems odd that the main, first, equation for the troposphere is using a power relationship, while the second is exponential. I can see how the second one is derived according to the derivation second, by why is the first used when temperature varies? Is it just an approximation? Shouldn't there be a single general purpose formula, at least for each layer?  Would like some expert input on this. -Cedderstk 12:14, 26 August 2018 (UTC)
thread_title:  Derivation of first equation 

message: def Altitude_to_Density(h): # Alt in meters about sea level
        # See https://en.wikipedia.org/wiki/Barometric_formula
        # Tested on https://www.digitaldutch.com/atmoscalc/
        #
        # height asl: h(m)  mass density: p(kg/m^3) standard temp: T(K)   temp lapse rate: L(K/m)
        table=[{'b':0,   'h':0,     'hto':11000,  'p':1.2250,   'T':288.15,  'L':-0.0065   },
               {'b':1,   'h':11000, 'hto':20000,  'p':0.36391,  'T':216.65,  'L':0.0       },
               {'b':2,   'h':20000, 'hto':32000,  'p':0.08803,  'T':216.65,  'L':0.001     },
               {'b':3,   'h':32000, 'hto':47000,  'p':0.01322,  'T':228.65,  'L':0.0028    },
               {'b':4,   'h':47000, 'hto':51000,  'p':0.00143,  'T':270.65,  'L':0.0       },
               {'b':5,   'h':51000, 'hto':71000,  'p':0.00086,  'T':270.65,  'L':-0.0028   },
               {'b':6,   'h':71000, 'hto':999999, 'p':0.000064, 'T':214.65,  'L':-0.002    }]
        #
        for layer in table: # Find the line we want
            if h >= layer['h'] and h < layer['hto']:
                break
        #
        R=8.3144598 # N·m/(mol·K) universal gas constant 
        g0=9.80665  # m/s2          gravity
        M=0.0289644 # kg/mol        molar mass of Earth's air
        #
        if layer['L']: # Formula 1
            p = layer['p'] * ( layer['T'] / (layer['T']+layer['L']*(h-layer['h'])) )**( 1 + (g0*M)/(R*layer['L']) )
        else: # Formula 2
            p = layer['p'] * math.exp( ( -g0*M*(h-layer['h']) ) / ( R * layer['T']  ) )
        #
        return p  — Preceding unsigned comment added by 2001:8000:1BED:6D00:F9F1:CD6:FEA5:C8E0 (talk) 06:38, 27 April 2020 (UTC)
thread_title:  Python equivalent 

message: It is probably worth mentioning that this is a really good example of a boltzmann distribution. There is a reason this is often an early problem in statistical thermodynamic courses. (Though admittedly on smaller systems like gas canisters, but the approximations make the equations the same when assuming constant temperature.) Zach7898 (talk) 07:59, 9 December 2023 (UTC)
thread_title:  Boltzmann Distribution