Pressure in atmosphere

Introduction

ISO2533:1975

The case in Toposhere (<10 km).

• Lapse rate +6.5 °C/km
• Base temp 19.0 °C
• Base atmospheric pressure 108,900 Pa equals 1.075 atm
• Base atmospheric density 1.2985 kg/m3

International Standard Atmosphere

https://en.wikipedia.org/wiki/International_Standard_Atmosphere

Consider the function in GY91's BMP280-3.3, eg at https://startingelectronics.org/tutorials/arduino/modules/pressure-sensor/

Earth's atmosphere's changes in

• Pressure $P$
• Temperature $T$
• Density $\rho$
• Viscosity $\eta$ or $\mu$

Hydrostatic balance ${\frac {dP}{dh}}=-\rho g$ The ideal gas law $P=\rho RT$

Reference atmospheric model

How the ideal gas properties change (mainly) as a function of altitude (etc).

Static atmospheric model

$\rho ={\frac {MP}{RT}}$ and $dP=-g\rho dh$ (see above).

Isothermal-barotropic approximation and scale height

Temperature and molecular weight are constant: density and pressure are exponential functions of altitude.

The US standard atmosphere

More realistic temperature function, consisting of eight data points connected by straight lines, which is---of course---an approximation.

https://en.wikipedia.org/wiki/U.S._Standard_Atmosphere

Barometric formula

Models how the pressure of the air changes with altitude with linear temperature change.

Ideal gas law $P={\frac {\rho }{M}}RT$, where pressure $P$ is a function of $n,T,V$, thus $P=P(n,T,V)$ and the hydrostatic assumption $dP=-\rho gdz$ are needed to derive this.

Assume ${\frac {dp}{dh}}=-\rho (h)g=-{\frac {N(h)m}{V}}g$ where $N(h)$ is the number of particles at altitude $h$. The ideal gas law states that $pV=NRT$, and thus $N=N(h)={\frac {p(h)V}{RT}}$. Finally, we have

${\frac {dp}{dh}}=-{\frac {N(h)m}{V}}g=-{\frac {p(h)V}{RT}}$

Simplified model from Weather.gov

https://www.weather.gov/media/epz/wxcalc/pressureAltitude.pdf

$h=44307.70\left(1-\left({\frac {p}{1013.25}}\right)^{0.190284}\right)$