Analytical Description and Vertical Structure of the Atmospheric Boundary Layer - Surface Based Remote Sensing of the Atmospheric Boundary Layer - page 24

Fig. 2.7 Vertical layering in a forest boundary layer. H gives the average tree height

An overview of the turbulence in the plant canopy sublayer and the air layer
just above it is given by Finnigan ( 2000 ). A more general overview is compiled in
Finnigan ( 2007 ).

2.5 Marine Boundary Layers

In contrast to all other boundary layer types, the marine boundary layer exhibits
special features due to the physical properties of the sea surface such as waves, the
large heat capacity of the water, and the large humidity transfer from the water to
the lower atmosphere.
The flexibility of the wavy water surface allows for a two-way interaction
between the air and the water. The wind can modify the sea surface by the forma-
tion of waves, and existing waves in turn can modify the air flow above them. This
leads to a complicated interaction between the wind fields in the marine boundary
layer and the wave fields on the ocean surface. The basic cycle of this interaction
can be described as follows. When the wind speed increases ahead of an approach-
ing atmospheric depression, waves (young waves in the sense of eq. ( 2.44 ) below)
are generated by frictional forces (tangential stress) and pressure forces (form drag)
(Banner and Peirson 1998 ) and grow as long as the downward momentum flux u

2
in the air is larger than the potential energy gh of the existing waves with wave height
h . The build-up of the waves is the more effective the longer the area is within which
the wind can act on the sea surface (the so-called fetch), and it takes some time to

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