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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
earth’s 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 Earth’s
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
1-2 km (3 max,
maybe)
Low Bowen ratio
Wave state
important
Continental
Strong diurnal
variability
Up to 5 km over
deserts
High Bowen ratio
Surface shape
fixed, but
important
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 lowlevel 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?