15
2
Atmospheric Boundary
Layer: Concepts and
Measurements
Gilberto Fisch
CONTENTS
2.1 Introduction .................................................................................................... 15
2.2 Defi nition of the Atmospheric Boundary Layer ............................................. 16
2.3 Measurements ................................................................................................. 18
2.4 Case Study: Amazonia ...................................................................................28
2.5 Concluding Remarks ...................................................................................... 30
References ................................................................................................................ 30
2.1 INTRODUCTION
The atmosphere is a gaseous layer that encompasses the Earth. It extends from the
surface up to a height around 500–600 km, and it is a vital medium for the living
conditions of the planet. Although its extension, the lower part of the atmosphere
(called “troposphere”) is the most important layer as almost all the atmospheric processes (especially the hydrologic cycle and its components like evaporation, convection, clouds, rain, etc.) occur inside this layer. Also, as the lowest part, it is where
the human beings live. The troposphere can be split into two layers: the lowest part
known as atmospheric boundary layer (ABL) (sometimes also referred to as planetary boundary layer—PBL) and the free atmosphere (FA), which lies between the
top of the ABL and the top of troposphere (which is around 15–17 km in the tropics).
However, for the air pollution issue, the ABL is the crucial layer to be understood as
the pollutants are released from tall chimneys or stacks at the surface, mainly due
to the anthropogenic sources. At the ABL, the pollutants are transported, diffused,
advected, mixed, dry and wet deposited, as well as chemically modifi ed. Another
important difference between the FA and the ABL is the nature of the fl ow: inside
ABL the fl ow is predominantly turbulent (and then provoking a well-mixed layer
(ML) during daytime or at unstable conditions) while the FA is mainly laminar.
The ABL plays an important role in meteorology, including studies of air pollution
dispersion and aeronautical and aviation procedures regarding aircraft landing and
takeoff. Also, the characteristics and behavior of the ABL by its turbulent exchange
© 2010 by Taylor and Francis Group, LLC
2
Atmospheric Boundary
Layer: Concepts and
Measurements
Gilberto Fisch
CONTENTS
2.1 Introduction .................................................................................................... 15
2.2 Defi nition of the Atmospheric Boundary Layer ............................................. 16
2.3 Measurements ................................................................................................. 18
2.4 Case Study: Amazonia ...................................................................................28
2.5 Concluding Remarks ...................................................................................... 30
References ................................................................................................................ 30
2.1 INTRODUCTION
The atmosphere is a gaseous layer that encompasses the Earth. It extends from the
surface up to a height around 500–600 km, and it is a vital medium for the living
conditions of the planet. Although its extension, the lower part of the atmosphere
(called “troposphere”) is the most important layer as almost all the atmospheric processes (especially the hydrologic cycle and its components like evaporation, convection, clouds, rain, etc.) occur inside this layer. Also, as the lowest part, it is where
the human beings live. The troposphere can be split into two layers: the lowest part
known as atmospheric boundary layer (ABL) (sometimes also referred to as planetary boundary layer—PBL) and the free atmosphere (FA), which lies between the
top of the ABL and the top of troposphere (which is around 15–17 km in the tropics).
However, for the air pollution issue, the ABL is the crucial layer to be understood as
the pollutants are released from tall chimneys or stacks at the surface, mainly due
to the anthropogenic sources. At the ABL, the pollutants are transported, diffused,
advected, mixed, dry and wet deposited, as well as chemically modifi ed. Another
important difference between the FA and the ABL is the nature of the fl ow: inside
ABL the fl ow is predominantly turbulent (and then provoking a well-mixed layer
(ML) during daytime or at unstable conditions) while the FA is mainly laminar.
The ABL plays an important role in meteorology, including studies of air pollution
dispersion and aeronautical and aviation procedures regarding aircraft landing and
takeoff. Also, the characteristics and behavior of the ABL by its turbulent exchange
© 2010 by Taylor and Francis Group, LLC