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?

• What is our current understanding of the PBL and what are the outstanding problems to be addressed?

Modeling the PBL Over Complex Terrain

Issues and Applications

Energy and mass exchanges at ground---interactions among soil science, hydrological cycles (ground and air), ecosystems, and atmosphere.•Canopy •Terrain•Heterogeneous surfaces•Clouds/fog•Urban environment, air pollution

Heig

ht

(m)

Planetary boundary layer

1 km

Surface heterogeneity

Internal boundary layer

fully adjusted

• Leaf stomatal control• Soil properties • Induced circulations• Internal boundary layer

Convective Internal Boundary Layers

Schematic diagrams of potential temperature profiles after changesin surface temperature (heat flux).

(a) development of an advectiveinversion after a hot-cold transition

(b) growth of a CIBL after a cold-Hot transition

(c) structure of a CIBL at longer fetch. Kaimal & Finnigan, 1994

Effects of Heterogeneity on Flux Measurement in the Surface Layer

Horst and Weil (1994, JTECH) show via modeling studies how far upstream surface fluxes originate that are measured via eddy correlation from a tower in the SL. This is known as the flux “footprint.” This is an important issue in flux measurement over heterogeneous terrain.

Note strong effectof stability on requiredfetch for flux measurement

/mz L

0 / mx z

Homogeneous

Heterogeneous /zi ~ 9