Outlines: Definisi, Struktur Lapisan Batas Atmosfer, Laminer dan Turbulen, Proses-proses dalam Lapisan Batas, Aplikasi, Kesimpulan

1. Andi Syahid Muttaqin (22412004)
Ashneel Chand (20212701)
ATMOSPHERIC
BOUNDARY
LAYER
ATMOSPHERIC SCIENCES (SB5224)
FACULTY OF EARTH SCIENCES
BANDUNG INSTITUTE OF TECHNOLOGY
2013

2. OUTLINES
o Definition
o ABL Structure
o Laminar and Turbulent Flow
o Processes in ABL
o Importance and Applications
o Summary/Synopsis

3. DEFINITION

4. o Atmospheric Boundary Layer (ABL) / is the
Layer bottom of the planetary atmosphere
formed by the interaction between the
atmosphere and the surface (land and ocean)
with a time scale of one day or less.
o Usually around 1 km deep.
o Temperatures vary diurnally.
o The surface influences the ABL by friction and
by heat fluxes.
o Characterized by turbulence, which is
generated by wind shear.
o All momentum exchange between the
atmosphere and the surface take place through
boundary layer.

5. STRUCTURE OF ATMOSPHERIC
BOUNDARY LAYER

8. Depth of ABL
o Over oceans: varies more slowly in space & time
because sea surface temperature varies slowly
respectively due to large specific heat of water
o Over land: varies more rapidly in space & time
because surface condition vary more rapidly
respectively
o In case of high pressure: the boundary layer
tends to be shallower near the center of high
pressure regions. This is due to the associated
subsidence and divergence.
o In case of low pressure: there is an updrafts and
often it is difficult to find the top of boundary
layer.

9. Boundary Layer Stability Condition
o Is determined by Richardson number (Ri).
o (is a convenient means of categorizing
atmospheric stability in the boundary layer)
o Ri: > 0 stable
= 0 neutral
< 0 unstable

10. o Boundary layer crucially upon its density
structure. i.e. whether layer is being heated or
cooled from beneath and upon distribution of
water vapour.
o Unstable boundary layer-situation arise because
of heating from below, boundary layer is
vigorously stirred & its properties to be quite
well mixed.

11. o Stable boundary layer- situation arise usually
caused by cooling from below, turbulence is
suppressed & there is little mixing except in
a layer close to the surface.

12. LAMINAR AND TURBULENT
FLOWS

13. Laminar Flow
o Where the fluid moves slowly in the layers,
without much mixing among the layers.
(Typically occurs when the velocity is low or the
fluid is very viscous).

14. Turbulent Flow
o Turbulent – the apparent chaotic nature of
many flows, which is manifested in the form
of irregular almost random fluctuations.

15. Reynolds Number
o Reynolds number can be used to
characterize laminar and turbulent flows:
o NR< 2000 – laminar flow
o NR> 4000 – turbulent flow
o 2000 < NR < 4000 – transition region or
critical region.

17. PROCESSES IN THE
ATMOSPHERIC BOUNDARY LAYER

18. Processes in ABL
o Factors Influencing
the ABL
o Weather Processes
o Pollutant Removal
Mechanism
o Evapotranspiration
o Exchange in ABL

19. Factors that Influence the ABL
o Energy Budgets
o Moisture
o Diurnal
Variations
o Buoyancy
o Shear
o Roughness Layer

20. Weather Processes in ABL
o Temperature and pressure gradients caused by
differential heating force the winds that drive air
masses together producing warm, cold and fronts.
o The lifting mechanisms, produce the upward motion
which causes the cooling necessary for cloud
development to occur and precipitation to form.
o Though, each of these processes are important in the
role they play in the production of various weather
events.

21. Orographic Lifting
Frontal System
Source: http://www.shodor.org/metweb/session6/

22. Pollutant Removal Mechanisms
o Wet deposition:
 acid rain,
 acid fog,
 fog,
 haze, and
 smog
o Dry deposition:
 aerodynamic,
 sub-layer, and
 surface
o Chemical reactions:
 Example reaction of acid rain: SO2 + moisture  H2SO4
Source: http://www.physicalgeography.net/fundamentals/8h.html

23. Evapotranspiration
o It is used to describe the
exhange of water vapor
from the surface to the
air via water reservoirs,
soils, and plant life.
o Evapotranspiration is,
therefore, an important
process within the
atmospheric boundary
layer.
o The amount of water vapor in the air varies from 0 to 4 percent
by evapotranspiration.
o Evapotranspiration is the combined process of evaporation and
transpiration.
Source: http://static.skynetblogs.be

24. Exchange in ABL
o What are exchanged in
ABL?
 Heat
 Momentum
 Masses (water vapour,
CO2, biogenic gasses,
pollutant, dust, spores,
pollen, seeds, smoked).
o Why does this process occur?
 Characteristics of the surface change with time.
 The surface characteristics are different
 Change the temperature of the air.
 Change the water content.
http://www.eoearth.org/article/Eddy_covariance_method?topic=49537

25. Main Causes of the Exchange
o Exchange momentum in ABL is mainly caused by turbulence
processes.
o Turbulence causes of highly efficient mixing: 106 more efficient
than molecular diffusion.
Source: http://apollo.lsc.vsc.edu/classes/met455/notes/section2/1.html

26. Example

27. Unit of Exchange
o The transfer of a quantity per unit area per unit
time is called a flux:
 Moisture flux
 Heat flux
 Momentum flux
 Eddies also transport
heat,
moisture,
momentum,
pollutant, etc.
o It’s not the mean flow that transport heat, moisture, etc.
from near surface up to the boundary layer, this is the role
of turbulence.

28. EddyMechanismStabilityMechanism
Eddy Flux and Stability
Example:
Eddy flux is defined
by (turbulent
heat flux).
When w‘ is
turbulent part of
vertical velocity and
θ’ is turbulent part
of potential
temperature.
''w

29. Mixing Height/Depth
o Because turbulent fluxes vary based on surface
heating and other factors, the height of the ABL also
varies.
o The height of the ABL is called the mixing height.
o The mixing height is very important to air quality
experts.

30. IMPORTANCE AND APPLICATIONS

31. ABL and Urban Climatology
o Urban climate is a mutual relationship of the urban
surface and atmospheric effects that occur on it.
o Conceptual scheme is very important in the study of
urban climatology in particular the study of the
Boundary Layer.
o The structure of the atmosphere boundary layer is well
understood over homogenous rural areas.
o On the other hand, the urban boundary layer requires
special treatment.
o This is especially important for nocturnal periods when
the atmosphere is stable and leads to the trapping of
pollutants near ground level.

32. Urban Boundary Layer

33. Diurnal Conditions
o During the day, the pollution is releases into the mixed layer.
o The convection within the mixed layer quickly disperses the
pollutants downwind.
o This is caused by rising thermals in some areas and
subsidence in others.
o The rapid mixing of particles in the mixed layer is beneficial
in that it prevents the build-up of pollution into dangerous
concentrations in any one area.
Source: http://www.shodor.org/metweb/session7/focus7.html

34. Nocturnal Conditions
o Pollutant released during the night from a tall stack would spread out
evenly, a process called coning.
o If a plume were released from a short stack within the stable layer,
the plume would not disperse very quickly and behave in the process
called fanning.
o Coning disperses particles more effectively than fanning. Fanning
disperses pollution in the horizontal, but not very effectively in the
vertical.
Source: http://www.shodor.org/metweb/session7/focus7.html

35. Disasters

36. NOAA-ARL
Research and Development
o The Air Resources Laboratory (ARL) uses state-of-
the-art methods and techniques, and develops
new ones as necessary, to better understand and
model the atmospheric boundary layer and air-
surface exchange processes.
o Few examples of ARL’s Atmospheric Boundary
Layer and Surface-Exchange Research and
Development are:
 DCNet (www.atdd.noaa.gov)
 Extreme Turbulence Probe
(www.noaa.inel.gov/capabilities/etprobe.htm)

37. DCNet
o The network currently has 10 stations, most of them on
building rooftops, which collect not only the standard
meteorological parameters but also measure characteristics
of atmospheric turbulence.
o The data have allowed researchers to determine the spatial
and temporal fluctuations of horizontal winds throughout
the District, as well as to characterize the atmospheric layer
immediately above the urban canopy where winds are
poorly predicted by meteorological models.
o The main goal of DCNet is to refine understanding of how
hazardous trace gases and particles are dispersed across the
kind of area where people work and live.

39. Extreme Turbulence Probe
o The ET Probe is designed to measure winds,
turbulence, and air-sea exchanges in conditions with
heavy rain and high winds, such as those encountered
in hurricanes.

40. Clear Air Turbulence (CAT)
Source: http://www.youtube.com/watch?v=lxlSZ-SB1XQ

41. Summary/Synopsis
 Definition
 ABL Structure
 Depth of ABL
 Boundary Layer Stability
Condition
 Laminar flow
 Turbulent flow
 Reynolds Number
 Processes in ABL
 Factors that influence the
ABL
 Weather Processes in ABL
 Pollutant Removal
Mechanisms
 Evapotranspiration
 Exchange in ABL
 Main causes of the
Exchange
 Unit of Exchange
 Eddy and Stability
 Mixing height/depth
 Importance and Applications
 ABL and Urban Climatology
 ARL Research and
Development
 DCNet
 Extreme Turbulence Probe
 Clear Air Turbulence (CAT)

42. Theodore Von Karman
(1881-1963)
“There are two great unexplained
mysteries in our understanding of
the universe.
One is the nature of unified
generalized theory to explain both
gravity and electromagnetism.
The other is an understanding of
the nature of turbulence.
After I die, I expect to God to
clarify the general field theory to
me.
I have no such hope for
turbulence.” – Theodore Von
Karman
.: Quotations :.

43. References
Air Resources Laboratory – Atmospheric Boundary Layer and Surface
Exchange Research and Development (www.arl.noaa.gov)
Atmospheric Boundary Layer Structure:
(http://lidar.ssec.wisc.edu/papers/akp_thes/node6.htm)
Baklanov A., Grisogono B. 2007. Atmospheric Boundary Layers. Nature,
Theory and Application to Environmental Modelling and Security.
Springer Science, New York.
Basic Meteorological Process:
(http://www.eng.utoledo.edu/~akumar/IAP1/NEWMET.htm)
DCNet: (http://www.atdd.noaa.gov/?q=node/15)
Extreme Turbulence Probe:
(www.noaa.inel.gov/capabilities/etprobe.htm)
Garrat J.R. 1992. The Atmospheric Boundary Layer. Cambridge University
Press, Cambridge.
General Boundary Layer Characteristics and Evolution:
(http://apollo.lsc.vsc.edu/classes/met455/notes/section2/index.html)

44. Kaimal J.C., Finningan J.J. 1994. Atmospheric Boundary Layer Flows, The
Structure and Measurement. Oxford University Press, New York.
Planetary Boundary Layer:
(http://kadarsah.wordpress.com/2011/07/01/planetary-boundary-layer-
pbl/)
Stewart R.W. 1997. The Atmospheric Boundary Layer. WMO No.523, World
Meteorological Organization.
Stull R.B. 1988. An Introduction to Boundary Layer Meteorology. Springer.
Surface Energy Budget Network (SEBN):
(http://www.atdd.noaa.gov/?q=node/23)
The Planetary Boundary Layer:
(http://www.cmmap.org/learn/climate/energy8.html)
The Planetary Boundary Layer:
(http://www.shodor.org/metweb/session7/session7.html)
Urban-Rural Campaign:
http://www.engr.ucr.edu/~marko/urban_rural_field_measurments.htm
Washington D.C. Mixing Height Study:
(http://www.atdd.noaa.gov/?q=node/79)

46. Appendices
Fig. Wind velocity profile

47. CAT – Invisible Trouble

49. Turbulence Forecast