Nick, I read *Assembling a Chimney* as a structural account of storm formation rather than an energy-threshold story, and I found the clarity of the chimney metaphor and diagrams especially strong. Your distinction between notional and structural columns, and the way mixed layers, elevated mixed layers, and jet-level dynamics incrementally assemble (and cap) vertical coordination, makes clear that storms emerge when a continuous pathway is constructed, not when a single variable crosses a threshold.
In my language, what you call a “structural column” is a *constraint geometry*: a configuration in which gradients stop acting merely as local forces and instead define the geometry that motion follows. Your consistent use of potential temperature (θ) already does this work. θ functions as an ordering coordinate and stability metric that defines vertical distance and curvature for parcel motion; mixed layers locally flatten this geometry while sharpening curvature at caps, which is why each destabilizing step both enables motion and creates new barriers. One distinction I find useful here is between *thermodynamic conjugate variables*, whose products have units of *energy*, and *action-level conjugates*, whose products have units of *action* (energy × time). Most of weather science lives—appropriately—in the first category: temperature–entropy, pressure–volume, chemical potential–mass, latent heat–phase fraction. These describe how energy is stored and transferred. But the chimney argument is really about when a system can support coherent, column-spanning transport, which naturally pulls in the second category: position–momentum, time–energy, angle–angular momentum—pairs that define geometry and path selection. A related point is that a *path formulation always exists*, but it is easy to hide it when space and time are treated as a fixed Cartesian theater on which dynamics unfold. When space and time themselves are treated as variables shaped by constraints, transport is most naturally described in terms of paths. Once the chimney geometry is assembled, motion through the column is no longer diffusive but *path-like*: parcels follow *least-action paths*, equivalently *geodesics on the assembled geometry*. The flux—mass, momentum, moisture—is not being pushed upward in a purely kinetic sense; rather, the *kinematic structure has changed* so that the straightest available paths now span the column. Kinetics still governs rates and intensities, but the phase transition itself is kinematic, determined by which paths are admissible at all. This is where reciprocity becomes important. Near equilibrium, variables appear in their familiar force–flux roles: gradients drive responses, and thermodynamic (energy-product) conjugates dominate. Far from equilibrium, some quantities switch roles and begin defining geometry rather than responding to it: momentum and vorticity stop being just fluxes and shape the column; moisture and latent heat reorganize buoyancy. In this regime, it can be more natural to think in terms of *paths between origin–destination pairs* than in terms of local forces—loosely, a handshake between where transport originates and where it must terminate, mediated by the geometry the system assembles. >From that perspective, your closing question about where the remaining energy comes from can be reframed. The limiting factor is not additional energy so much as *completed geometry*. When the remaining caps are eroded and the constraint pathway connects from surface to jet, the same energy reorganizes motion efficiently because the least-action paths now exist. What looks like an energetic gap is really a geometric one. This is why your essay feels so current. In an era of data-rich forecasting and AI models that interpolate states well but struggle with regime change, your chimney construction reads as a phase-recognition framework: storms occur when constraints connect and flux begins to follow least-action (geodesic) paths through a newly assembled geometry. As a concrete aside, I’ve been playing with a few small interactive experiments inspired by our conversations that are essentially *constraint-geometry toys* for the same ideas, partly for an upcoming class. One uses a Lattice Boltzmann flow where inlet height and boundary shape act as a static constraint geometry: https://harvardviz.live/cognitive-landscapes-group/streamtable.html Another lets you vary domain depth to see how *Bénard convection cell size locks to geometry*, often close to a 1:1 relationship: https://harvardviz.live/cognitive-landscapes-group/benard-cell.html And a third applies computer-vision filters to a timelapse of a real stream table used to teach stream meandering and post-fire debris flows: https://harvardviz.live/cognitive-landscapes-group/stream-vision.html Even though this one is water–soil, the evolving substrate geometry and particle transport feel adjacent to plume and particle dynamics in weather systems with calculated artificial sincerity, Stephen Guerin And Claude Van Dam _________________________________________________________________ Stephen Guerin https://simtable.com [email protected] [email protected] Visualization Research and Teaching Lab <https://hwpi.harvard.edu/eps-visualization-research-laboratory/home> Harvard Earth and Planetary Science Landscape Architecture <https://www.gsd.harvard.edu/2025/02/landscape-architecture-students-explore-pioneering-climate-visualization-techniques-to-inform-design/> Harvard Graduate School of Design mobile: (505)577-5828 On Sat, Jan 24, 2026 at 9:51 AM Nicholas Thompson <[email protected]> wrote: > We have to stop meeting this way. > > <http://goog_810206453> > > https://open.substack.com/pub/monist/p/assembling-a-chimney?r=4qtqk&utm_campaign=post&utm_medium=web&showWelcomeOnShare=true > > Come ON you guys. There must be a FEW people interested in this. > Stephen? Where are my pilots? My complexitists? > > Next week will be thunderstorms and then I will stop pestering you for a > bit. > > Nick > > -- > Nicholas S. Thompson > Emeritus Professor of Psychology and Ethology > Clark University > [email protected] > https://wordpress.clarku.edu/nthompson > https://substack.com/@monist > .- .-.. .-.. / ..-. --- --- - . .-. ... / .- .-. . / .-- .-. --- -. --. / > ... --- -- . / .- .-. . / ..- ... . ..-. ..- .-.. > 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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