16
Air Pollution and Turbulence: Modeling and Applications
processes is very important and crucial in determining the local weather. Most of the
numerical weather models have an ABL submodel in order to quantify the energy
partition at the surface and the turbulent exchange of momentum, heat/water, and
matter between the surface and the FA. The ABL connects these two layers.
Traditionally, micrometeorology is one of the branches of meteorology, and it
deals with the atmospheric phenomenon that occurs at the ABL, mainly at the surface. Over the last decades, the subject of boundary layer meteorology has appeared
at the scientifi c community and used with or in connection with micrometeorology. It deals with the processes that occur above the surface layer, connecting the
surface and the FA. The clouds are a good example how to link the surface and FA
by different processes (evaporation, convection, condensation, precipitation, etc.).
All these processes involve transport of energy. Garstang and Fitzjarrald (1999)
described very well these interactions, especially considering the sea–atmosphere
interface.
The goal of this chapter is to introduce this important layer (ABL), the actual
devices available for the measurements with their advantages and disadvantages,
presenting some results for the fi eld measurements in Amazonia.
2.2 DEFINITION OF THE ATMOSPHERIC BOUNDARY LAYER
The ABL is the lower part of the troposphere and from the meteorological point of
view it plays an important role connecting the surface with the FA (above 1–2 km).
The FA is governed by atmospheric processes at synoptic or large scale like the horizontal pressure gradients, cold fronts, atmospheric disturbances, etc. At this layer,
because the time and space scale of the phenomena, the Coriolis effect (due to the
movement of the Earth) must be considered. By the other side, the ABL is mainly
determined by local processes such as topography, surface roughness variation, vegetation contrast, and soil moisture.
Following the defi nition by Garrat (1992), the ABL is the part of the atmosphere
that is directly infl uenced by the surface processes (like friction and the diurnal cycle
of heating and cooling) and responds to this external forces of about a timescale less
than a day. Stull (1988) gave a similar defi nition but emphasized the timescale being
less than 1 h. Associated with the external forces, there is signifi cant turbulent fl uxes
of momentum, heat, and matter carried by turbulent motions (made by eddies) on a
spatial scale of 1–2 km (largest eddies). The characteristics and time evolution of the
ABL are governed by the turbulence and much of this turbulence is generated from
the forces from the ground (thermals, frictional drag–shear, obstacle).
Consequently, the ABL can be split into two layers: an atmospheric surface layer
(ASL) extending from the surface up to a height of 120–150 m and an outer layer
from the top of the surface layer up to the FA. The ASL is the region at the bottom of the ABL where turbulent fl uxes are almost constant (varies less than 10%
of their magnitude) and turbulence is continuously being generated and/or dissipated. Besides that, it is also part of the diurnal cycle. The outer layer, which has a
pronounced diurnal cycle, can be called convective boundary layer (CBL) or stable
boundary layer (SBL) depending on the predominant atmospheric stability. The CBL
is produced by the strong heating of the surface, which produces thermal instability
© 2010 by Taylor and Francis Group, LLC
Air Pollution and Turbulence: Modeling and Applications
processes is very important and crucial in determining the local weather. Most of the
numerical weather models have an ABL submodel in order to quantify the energy
partition at the surface and the turbulent exchange of momentum, heat/water, and
matter between the surface and the FA. The ABL connects these two layers.
Traditionally, micrometeorology is one of the branches of meteorology, and it
deals with the atmospheric phenomenon that occurs at the ABL, mainly at the surface. Over the last decades, the subject of boundary layer meteorology has appeared
at the scientifi c community and used with or in connection with micrometeorology. It deals with the processes that occur above the surface layer, connecting the
surface and the FA. The clouds are a good example how to link the surface and FA
by different processes (evaporation, convection, condensation, precipitation, etc.).
All these processes involve transport of energy. Garstang and Fitzjarrald (1999)
described very well these interactions, especially considering the sea–atmosphere
interface.
The goal of this chapter is to introduce this important layer (ABL), the actual
devices available for the measurements with their advantages and disadvantages,
presenting some results for the fi eld measurements in Amazonia.
2.2 DEFINITION OF THE ATMOSPHERIC BOUNDARY LAYER
The ABL is the lower part of the troposphere and from the meteorological point of
view it plays an important role connecting the surface with the FA (above 1–2 km).
The FA is governed by atmospheric processes at synoptic or large scale like the horizontal pressure gradients, cold fronts, atmospheric disturbances, etc. At this layer,
because the time and space scale of the phenomena, the Coriolis effect (due to the
movement of the Earth) must be considered. By the other side, the ABL is mainly
determined by local processes such as topography, surface roughness variation, vegetation contrast, and soil moisture.
Following the defi nition by Garrat (1992), the ABL is the part of the atmosphere
that is directly infl uenced by the surface processes (like friction and the diurnal cycle
of heating and cooling) and responds to this external forces of about a timescale less
than a day. Stull (1988) gave a similar defi nition but emphasized the timescale being
less than 1 h. Associated with the external forces, there is signifi cant turbulent fl uxes
of momentum, heat, and matter carried by turbulent motions (made by eddies) on a
spatial scale of 1–2 km (largest eddies). The characteristics and time evolution of the
ABL are governed by the turbulence and much of this turbulence is generated from
the forces from the ground (thermals, frictional drag–shear, obstacle).
Consequently, the ABL can be split into two layers: an atmospheric surface layer
(ASL) extending from the surface up to a height of 120–150 m and an outer layer
from the top of the surface layer up to the FA. The ASL is the region at the bottom of the ABL where turbulent fl uxes are almost constant (varies less than 10%
of their magnitude) and turbulence is continuously being generated and/or dissipated. Besides that, it is also part of the diurnal cycle. The outer layer, which has a
pronounced diurnal cycle, can be called convective boundary layer (CBL) or stable
boundary layer (SBL) depending on the predominant atmospheric stability. The CBL
is produced by the strong heating of the surface, which produces thermal instability
© 2010 by Taylor and Francis Group, LLC