Transcript 3-Dimensonal Structure of Atmospheric Boundary Layer

Observed Structure of the
Atmospheric Boundary Layer
(2)
Review of last lecture
• Vertical structure of the atmosphere and
definition of the boundary layer
• Vertical structure of the boundary layer
• Definition of turbulence and forcings
generating turbulence
• Static stability and vertical profile of virtual
potential temperature: 3 cases. Richardson
number
• Boundary layer over ocean
Boundary Layer depth:
Lidar
Boundary Layer depth:
Lidar
Turbulence inside the boundary layer
Boundary Layer depth:
Effects of diurnal forcing over land
• Daytime convective mixed layer + clouds (sometimes)
• Nocturnal stable boundary layer + residual layer
Convective mixed layer (CML):
Growth
The turbulence (largely the
convectively driven
thermals) mixes (entrains)
down potentially warmer,
usually drier, less turbulent
air down into the mixed
layer
Convective mixed layer (CML):
Vertical profiles of state variables
Strongly stable
lapse rate
Nearly
adiabatic
Super-adiabatic
Well-mixed (constant profile)
Nocturnal boundary layer over land:
Vertical structure
• The residual layer is the
left-over of CML, and has
all the properties of the
recently decayed CML. It
has neutral stability.
• The stable boundary
layer has stable stability,
weaker turbulence, and
low-level (nocturnal) jet.
Weakly stable lapse rate
Nearly adiabatic
Strongly stable lapse rate
Comparison between day and night
Strongly stable lapse rate
Nearly
adiabatic
Super-adiabatic
Kaimal and Finnigan 1994
Weakly stable lapse rate
Nearly
adiabatic
Strongly stable lapse rate
•
Subtle difference between convective mixed layer and residual layer:
Turbulence is more vigorous in the former
Summary
• Daytime: convective mixed layer + clouds
(sometimes)
• Nocturnal: stable boundary layer + residual
layer