# Langmuir circulation Wind blowing steadily over water organises the surface layer into long counter-rotating rolls aligned nearly with the wind. Between adjacent rolls the flow converges, and anything buoyant — foam, seaweed, plastic — collects into the parallel streaks anyone who has looked at a lake on a windy day has seen. Irving Langmuir worked out the mechanism in the 1930s after noticing seaweed lines in the Sargasso Sea. ## Microsim — p5.js Sidecar: `Langmuir_circulation.p5.js` · route leaf: `microsim/p5js/Langmuir_circulation__20260910T0400Z`. Built to the Betterfire Standard v0 (single `ARTICLE` constant, HUD title and Wikitube URL, control hints, parameter readout and equation). | Control | Does | |---------|------| | `wind slider` | wind stress driving the rolls | | `spacing slider` | roll width | | `[c]` | clear and reseed the floaters | *What to watch:* Raise the wind and the rolls tighten; floating particles slide sideways into the convergence lines and stay there. Drop the wind and the streaks wash out. ## Rolls from waves and shear The rolls come from an interaction between the wind-driven shear current and the orbital motion in surface [[Wind_wave|waves]] — the wave field tilts and stretches the shear's [[Vorticity]] into streamwise tubes, and the instability grows. It is a close relative of the roll structures in [[Rayleigh–Bénard_convection]], but driven by wave–current interaction rather than by buoyancy, which is why it appears in warm water where there is no thermal instability at all. ## Why it matters Langmuir cells stir the upper ocean far more efficiently than [[Diffusion]] or plain shear [[Turbulence]] would, deepening the mixed layer and setting how fast heat and gases exchange with the [[Atmosphere_of_Earth|atmosphere]]. The convergence lines concentrate floating material, which is one reason marine debris gathers in windrows. For the same reason they concentrate buoyant plankton and the things that eat them, making the streaks visible [[Ecosystem|ecology]] as well as visible [[Turbulence|mixing]]. **Reads with:** *Introduction to Physical Oceanography (Robert H. Stewart, 2008)* — [OTL record](https://open.umn.edu/opentextbooks/textbooks/introduction-to-physical-oceanography) · [download](https://github.com/introocean/introocean-en/releases/tag/v20200229) · CC BY-NC-SA. Section 7 of the [[PORTAL_Thury_Hydrodynamics_Apex_Spine|Apex Spine]] book shelf. **On the spine:** [[Wind_wave]] · [[Vorticity]] · [[Thermocline]] · [[Rayleigh–Bénard_convection]] · [[WT!Thury_Hydrodynamics_Compendium]]. ## Wikipedia : Wikitube **Strict pair:** [Wikipedia](https://en.wikipedia.org/wiki/Langmuir_circulation) : [Wikitube](https://en.wikitube.io/wiki/Langmuir_circulation) ## Previous hub tags Hubs: `Life_Physics`, `Systems`. Portals: [[PORTAL_Thury_Hydrodynamics_Apex_Spine]], [[PORTAL_WT!Thury_Hydrodynamics_Compendium]], [[PORTAL_Physics]]. --- *Book-section wave · 2026-09-10 · article + p5 microsim shipped together.*