Barometric pressure, conversion from Inches to millibars,vice verso?

Question

I am an amateur meteorologist and would like a factor to convert inches of mercury to millibars and back. Thank you.
Michael C

Answer 1

Mike, let me show you how to convert using "first principles".

pressure P = force F/ unit area A

force F = mass m x acceleration due to gravity g

therefore P = mg/A (1)

density R = mass m/ unit volume V

Volume V = cross-sectional area of a barometer A x height of the liquid H

therefore M = R x A x H (2)

substitute (2) into (1)

P = R x A x H x g/ A = R x H x g (3)

let P = 30 in of mercury which we let equal H

so then H = 30 x 2.54 cm

R(mercury) = 13.534 gm per cubic centimeter

g = 980 cm per seconds squared

Therefore P = 30 x 2.54 x 13.534 x 980 gm cm sec-2/cm2

or P = 1010665 dynes/cm2

now mb = 1000 dynes/cm2

therefore P = 1010.665 mb = 30 in mercury (4)

It is from (4) that we find that 1 inch mercury = 33.68 mb

As a meteorologist you need to know how to do these kind of problems from first principles. In other words, using the fundamental physical laws and equations.

Answer 2

Barometric pressure is not involved in the equation, not at the levels that we are interested in. It could have an influence in three ways: 1. Barometric pressure so high (and we'd be talking extreme) that one would have to account for the mass of the atmosphere when calculating the gravity of a planet. For example, if Jupiter has a 'surface' way down below all that gas atmosphere, we would have to subtract the mass of the atmosphere from the total mass of the planet, in order to determine the 'surface' gravity. We would also have to do the analysis of number 2. Does not apply to Mars. 2. Barometric pressure so high that it might affect an athlete's performance (other than whether she can breathe, I mean). For example, on Venus, it might be possible, by wearing helium inflated suits and webbed hands (and winged arms) to increase a person's hang time in otherwise normal sports. The atmosphere is thick enough to gain a few seconds by 'swimming' through it. Does not apply to Mars. 3. The barometric pressure might be low enough that protection (and air breathing apparatus) is needed. This may hamper an athlete's performance. Normally, this would not improve hang time. However, the reduced friction would not provide a calculable advantage. This may apply to Mars.

Answer 3

inches of mercury x 33.864 = millibars

millibars x 0.02953 = inches of mercury

Answer 4

google it
see below