Exploring the Role of Convection in Atmospheric Lapse Rate
This blog post explores the role of convection in atmospheric lapse rate, and how it is derived from the ideal gas law combined with the first law of thermodynamics. It looks at the dry lapse rate, and how things become more complicated with a moist atmosphere.
Prof Michael E. Mann
Scientist/Author; Pres Dist Prof/Director Center for Sci, Sustain. & the Media, U. Penn; Nat Acad of Sci.; Tyler Prize; Mastodon: @MichaelEMann@fediscience.org
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The cooling with elevation (lapse rate) can be derived from the ideal gas law combined with the first law of thermodynamics. It has nothing to do with convection. We teach this to first year undergrads. https://t.co/GhpaKjOUJH
— Prof Michael E. Mann (@MichaelEMann) April 2, 2023 -
That's the dry lapse rate of course (which he was presumably referring to). With a moist atmosphere, things are more complicated, because the condensation of water vapor is involved. Convection is only peripherally involved in its role with the vertical transport of water vapor.
— Prof Michael E. Mann (@MichaelEMann) April 2, 2023 -
p.s. there is an assumption of isentropic/adiabatic behavior (i.e. no external heating). Again, convection has nothing to do with it.
— Prof Michael E. Mann (@MichaelEMann) April 2, 2023 -
I forgot to mention, vertical force balance comes into it as well (the so-called "hydrostatic approximation", which requires that the vertical pressure gradient force balances gravitation force). Again, convection doesn't come into it.
— Prof Michael E. Mann (@MichaelEMann) April 2, 2023 -
Here @SenatorRennick, from my lecture notes. I await your critique of the derivation! pic.twitter.com/6QBgVZDcJf
— Prof Michael E. Mann (@MichaelEMann) April 2, 2023 -
In fact, Senator, convection is doing just the opposite of what you claim, tending to *relieve* the gravitational instability of warmer (less dense) air below colder (more dense) air.
— Prof Michael E. Mann (@MichaelEMann) April 2, 2023