Boundary Layer Meteorology - UMD

Boundary Layer Meteorology - UMD

Boundary Layer Meteorology Prof. Daniel Kirk-Davidoff Rm. 3423 CSS (301)-270-3704 [email protected] Lecture 1 8/31/04

Course Syllabus: discuss requirements, schedule, readings. Starting Point Exam Introduction to the Boundary Layer Hand out readings Introduction to the Boundary Layer Definitions: Stull: that part of the troposphere

that is directly influenced by the presence of the earths surface, and responds to surface forcings with a timescale of about an hour or less Introduction to the Boundary Layer Definitions: Garratt:the layer of air directly above the Earths surface in which the effects of the surface (friction, heating and cooling

[and moistening]) are felt directly on time scales of less than a day, and in which significant fluxes of momentum, heat or matter are carried by turbulent motions on a scale of the order of the depth of the boundary layer or less. Things that happen in the boundary layer Large diurnal temperature variations (relative to the free troposphere above). Turbulence

Sources of turbulence: Thermal forcing (thermals: buoyant eddies forced by solar heating of the surface) Vertical wind shear (due to frictional drag by the surface on geostrophic flow aloft)

Things that happen in the boundary layer Horizontal wind shear (due to flow of wind around obstacles: trees, mountains, islands) Waves (gravity) Spiraling Winds Katabatic (drainage) Winds Nocturnal Jet Things that happen in the

boundary layer Clouds: Fair weather cumulus clouds (whose roots are in the BL) Trade cumulus (which may rain) Stratocumulus clouds (which may rain) Fog Kinds of atmospheric boundary layers Stable

Near-Neutral Convective Kinds of atmospheric boundary layers Marine Little diurnal variability Continental Strong diurnal

variability 1-2 km (3 max, maybe) Low Bowen ratio Up to 5 km over deserts High Bowen ratio

Wave state Surface shape Read ch. 1 of Garratt, and answer: Why is the mean structure of the boundary layer very much dependent on the season? When and why is the structure of the boundary layer over the ocean similar to that over land in extra-tropical latitudes?

Otherwise, why is the marine boundary layer usually shallower than over the land? Read ch. 1 of Garratt, and answer: Why is information on the likely growth of the shallow mixed layer of particular importance to the dispersal of smog and low-level pollutants? How does dewfall and frost formation depend on the state of the

atmospheric boundary layer (ABL)? Read ch. 1 of Garratt, and answer: Why is w anticorrelated with any other property fluctuation in figure 1.4?

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