The Lifecycle of the Convective Boundary Layer: Morning Transition

22 Pages·2008·1.17 MB·English

by  Wayne Angevine

Atmospheric Boundary Layer Activities in ESRL
Wayne M. Angevine
With help from:
the Surface and PBL theme team
Sara Tucker
Bob Banta
Ola Persson
Jim Wilczak
Chris Fairall
Atmospheric Boundary Layer
Diurnal Variation

(a severe simplification)

2000
Inversion
1500
)
s
r
e
t
e
m Convective
( Mixed Layer
t 1000 Residual Layer Residual Layer
h
g
i
e
H
500
SSttaabbllee ((nnooccttuurrnnaall)) LLaayyeerr
0
Sunrise Noon Sunset Sunrise
Adapted from Introduction to Boundary Layer Meteorology -R.B. Stull, 1988
Coastal Boundary Layer
- warm to cold

(cid:190) One of many
2000
“other” types of
boundaInvreyrs ion
1500
) layers
s
r
e
t
(cid:190)e Polar BLs are
m Convective
( Mixed Layer
t s10t0a0bleRe sfidoural Lloaynerg Intermediate
h
g Layer
i periods
e
H
(cid:190) Some oceanic
500
BLs are
continuously
StableS mtaabrlien (en booctuunrdnaarl)y Llaayyeerr
0
weakly
convective
Sunrise
Why do we care about
the boundary layer?
(cid:190) Controls transport of pollutants and climate-forcing
constituents
(cid:190) Source of heat, water, and turbulence
(cid:190) Vital for weather and climate prediction
(cid:190) Location of aerosols, clouds, and pollutants
(cid:190) Context for other measurements
Almost any measurement or prediction
involves the boundary layer
Critical scientific gaps
Grand challenges
(cid:190) Cloud formation and transitions within the boundary
layer
(cid:190) Concentration and transport of pollutants in
realistically variable boundary layer structures
(cid:190) Factors affecting the vertical transport of heat and
matter during the boundary layer daily cycle
(cid:190) Partitioning of various causes of climate changes in
the polar regions
(cid:190) Interaction between the boundary layer and
atmosphere above (free troposphere)
Recent findings
(cid:190) Cloud formation and transitions within the boundary layer
• Cloud effects on pollutant concentration and transport
• Aerosol effects on clouds
(cid:190) Conce ntration and transport of pollutants in realistically variable
bounda ry layer structures
• Stable boundary layer characterization
• Mixing depths over water
(cid:190) Factor s affecting the vertical transport of heat and matter during the
bounda ry layer daily cycle
• Coastal pollutant transport
• Parameterizations for mesoscale models – validation and development
• Au tomated BL height detection
(cid:190) Partitio ning of various causes of climate chang es in the polar regions

• Arctic boundary layer characterization
(cid:190) Interaction between the boundary layer and atmosphere above (free
troposp here)
• Transitional boundary layers
• BL-top entrainment
• Lin ks to larger scales
Mixing depths over the
Gulf of Mexico and Galveston Bay
(cid:190) Measurements from High
Resolution Doppler Lidar on
the Ronald H. Brown
(cid:190) Reliability enhanced by multiple
parameters
• aerosol backscatter
• turbulence intensity
• win d shear
(cid:190) Key fin ding: BL over water is
weakly convective
• shallow but not very shallow
• no diurnal cycle
(cid:190) Backed up by sea surface flux
and tem perature
measurements
(cid:190) Key to interpretation of in-situ
chemistry and aerosol
measurements
Validation of diurnal cycle in
forecast models
(cid:190) Using BL heights
derived by an
automated
algorithm for 5
radar wind profilers
in Texas
(cid:190) Average over 52
days
Stable boundary layer structure
(cid:190)Two types lead to
different chemical and
physical behavior
Weak LLJ Stronger LLJ (cid:190)Closely tied to
strength of low-level jet:
Weak LLJ (< 3 m s-1)
- O → 0
3

6-7 m s-1 or more

- [O ] stays > 20 ppb
3

(cid:190)Similar effects on

temperature and water
vapor profiles
Stable boundary layer structure
(cid:190) Decoupling of flow aloft from surface friction (cid:198) acceleration after
sunset
(cid:190) Happens every night to some degree
(cid:190) Doppler lidar provides highly resolved wind and turbulence information
(cid:190) A challenge to model parameterizations, and a framework for improving
them