Atmospheric boundary layer

The lowest part of the atmosphere, directly affected by the surface through friction, heat, and moisture exchange. Its depth and structure change over hours as surface conditions and weather vary.

Turbulent kinetic energy: The kinetic energy associated with fluctuating, irregular air motion. Its production and dissipation govern turbulent mixing through the layer.
Sensible heat flux: The rate of heat transfer between a surface and air that changes air temperature. Its upward daytime transfer drives buoyant mixing; downward nighttime transfer stabilizes air.
Air pollution dispersion: The transport and dilution of pollutants by atmospheric motion and mixing. Layer depth and turbulence determine how quickly surface emissions disperse.
Diurnal boundary layer cycle: The daily transition between a daytime convective layer, an evening transition, and a nighttime stable layer. It captures the layer’s most familiar cycle of growth, collapse, and rebuilding.
Atmospheric turbulence: Irregular atmospheric motion that mixes momentum, heat, moisture, and other substances. Boundary-layer turbulence remains difficult to represent across its full range of scales.
Monin–Obukhov similarity theory: A framework relating near-surface turbulent fluxes to atmospheric stability and height. It describes how surface-layer wind and temperature profiles shift with stability.
Latent heat flux: The rate of energy transfer associated with evaporation or condensation of water. Evaporation couples moisture exchange to the layer’s heat and buoyancy budgets.
Urban heat island: The tendency for built-up areas to be warmer than surrounding rural areas. Urban heat storage and roughness alter the layer’s temperature and mixing.
Nocturnal boundary layer: The nighttime atmospheric layer, usually stable near the ground and often capped by residual mixed air. It illustrates how surface cooling reorganizes turbulence after sunset.
Large eddy simulation: A computational method that resolves large turbulent motions and models smaller ones. It offers detailed simulations but still depends on approximations for unresolved eddies.

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