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Observations and Models of Boundary-Layer Processes Over Complex Terrain. What is the planetary boundary layer (PBL)? What are the effects of irregular terrain on the basic PBL structure? How do we observe the PBL over complex terrain? What do models tell us?
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(After Maria Agnesi; Milano, Italy, 1748)
roughness length and downwind roughness length
We define internal BL by (subscript θ for temperature and c for other scalars). The simplest formulations for are of the form
(analogous to BL growth on a smooth flat plate in wind tunnel experiments.)
A more sophisticated approach is to assume vertical diffusion then,
With this gives reasonable agreement
With observations. (Works best from smooth to
The thermal energy balance at the bottom of the surface layer
is conventionally written as
Rn = H + λeE + Gs ,
where Rn is the net radiation: short- and long-wave incoming
minus outgoing, H is the sensible heat flux, λeE is the latent
heat flux, and Gs is the heat flux going into storage in the soil
On surfaces with different angles of slope and
aspect ratio at 40 ° N latitude for:
(a) the equinoxes (21 March and 21 September)
(b) summer solstice (22 June)
(c) winter solstice (22 December)
Radiation incident upon
Slopes of differing angle and
Aspect ratio at 45 ° N at the
times of the equinoxes
(21 March and 21 September).
Time sequence of valley inversion destruction along with potential temperature
profile at valley center (left) and cross-section of inversion layer and motions
(a) nocturnal valley inversion (b) start of sfc. warming after sunrise
(c) shrinking stable core & start of slope (d) end of inversion 3-5 hrs. after
breezes sunrise (Oke, 1987, based on
Normalized surface-layer velocity standard deviations for near neutral conditions in the Adige Valley in the northern Italy alpine region. a is from Panofsky and Dutton, 1984; b the average values
from MAP; e/u*2is the normalized turbulence kinetic energy
(From de Franceschi, 2002).
Belcher, S.E. and J.C.R. Hunt, 1998: Turbulent flow over hills and waves. Annu. Rev. Fluid Mech.. 30:507-538.
Blumen, W., 1990: Atmospheric Processes Over Complex Terrain. American Meteorological Society, Boston, MA.
Geiger, R., R.H. Aron and P. Todhunter, 1961: The Climate Near the Ground. Vieweg & Son, Braunschweig.
Kaimal, J.C. and J.J. Finnigan, 1994: Atmospheric Boundary Layer Flows. Oxford Univ. Press, New York.
Oke, T.R., 1987: Boundary Layer Climates. Routledge, New York.
Venkatram, A. and J.C. Wyngaard, Eds.,1988: Lectures on Air Pollution Modeling. American Meteorological Society, Boston MA.
Abstracts from the10th Conference on Mountain Meteorology, 17-21 June 2002, Park City, UT, American Meteorological Society, Boston.Suggestions for Further Reading