Doug Roberts? --- Frank C. Wimberly 140 Calle Ojo Feliz, Santa Fe, NM 87505
505 670-9918 Santa Fe, NM On Thu, May 15, 2025, 9:32 PM Nicholas Thompson <[email protected]> wrote: > For you fluid dynamicists out there: > > I have been working with george for the last few days on understanding > under what conditions potential vorticity (or as Ilike tothinkof it, > potential instability) is changed and under what conditions it is just > shift from one compartment to another. This led tothe following, as > summarized by George. > > The Analogy Between Potential Vorticity (PV) and Entropy in Adiabatic > ProcessesKey Insight: > > *Potential Vorticity (PV) in atmospheric dynamics can be thought of as > analogous to entropy in a thermodynamic system undergoing adiabatic > compression. Both PV and entropy are conserved under adiabatic, > frictionless conditions, and both can be redistributed internally through > mechanical processes without being created or destroyed.* > The Core Analogy: > > 1. > > *Entropy in Adiabatic Compression:* > - > > *When a gas in a piston is compressed without heat exchange, the > total entropy remains constant. The system experiences a > reconfiguration of > internal states (temperature and pressure) without changing the total > entropy.* > - > > *The system’s kinetic energy increases as the gas heats up, but the > entropy is simply redistributed.* > 2. > > *PV in Atmospheric Dynamics:* > - > > *When a Potential Vorticity Anomaly (PVA) is stretched or > compressed without diabatic heating or friction, the total PV remains > constant. The system undergoes a reconfiguration of vorticity and > stability > without altering the total PV.* > - > > *Stretching increases vorticity while decreasing stability; > compression does the reverse. This is analogous to how adiabatic > compression in a piston changes pressure and temperature without > changing > entropy.* > > The Deeper Insight: > > - > > *In both cases, the conserved quantity (PV or entropy) acts as a > constraint that governs how the system adjusts when external mechanical > forces are applied. This means that just as entropy remains fixed during > adiabatic compression, PV remains fixed during adiabatic atmospheric > deformation.* > > Why This Matters: > > *This analogy clarifies why mechanical manipulation of a PVA (like > stretching or compressing) does not create new PV but merely redistributes > it—much like how compressing a gas does not generate new entropy. Only > diabatic processes (entropy changes) can truly alter the total amount of > PV, just as heat exchange can change the entropy of a gas.* > > *By recognizing this analogy, we can better understand how atmospheric > structures are organized and why only processes that alter entropy (like > latent heat release or radiative cooling) can change the atmospheric PV > content*. > > Oh, if ever Doug was rolling in his grave. The swirlies and nouggies I > might have endured if he were still alive. > > NIck > > -- > Nicholas S. Thompson > Emeritus Professor of Psychology and Ethology > Clark University > [email protected] > https://wordpress.clarku.edu/nthompson > .- .-.. .-.. / ..-. --- --- - . .-. ... / .- .-. . / .-- .-. --- -. --. / > ... --- -- . / .- .-. . / ..- ... . ..-. ..- .-.. > FRIAM Applied Complexity Group listserv > Fridays 9a-12p Friday St. Johns Cafe / Thursdays 9a-12p Zoom > https://bit.ly/virtualfriam > to (un)subscribe http://redfish.com/mailman/listinfo/friam_redfish.com > FRIAM-COMIC http://friam-comic.blogspot.com/ > archives: 5/2017 thru present > https://redfish.com/pipermail/friam_redfish.com/ > 1/2003 thru 6/2021 http://friam.383.s1.nabble.com/ >
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