Elements of the Sun; Solar Radiation

1
Chapter 4 The Energy Balance of The Surface

• Why The SEB?
• What and How?
• SEB components (Rn, SH, LE, G, B, Tskin, e, a,
  examples)
• ABL (neutral, stable, unstable, Ri, z/L,
  entrainment, LCL, eddy covariance, bulk
  formulations, examples)
• SEB measurements
• SEB remote sensing
• SEB modeling (LSMs)
• International Programs (GEWEX)

Kiehl and Trenberth (1997)
2
The Atmospheric Boundary Layer
ABL The part of the troposphere that is
directly influenced by the presence of the
earths surface, and responds to surface forcings
with a time scale of about an hour or less. See
http//lidar.ssec.wisc.edu/papers/akp_thes/node6.h
tm http//apollo.lsc.vsc.edu/classes/met455/notes/
section9/1.html
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The Atmospheric Boundary Layer

• Definition ABL The part of the troposphere
  that is directly influenced by the presence of
  the earths surface, and responds to surface
  forcings with a time scale of about an hour or
  less.
• Structure free atmosphere, entrainment zone,
  mixed layer (where U, ?, q almost constant with
  height), surface layer (where vertical fluxes of
  momentum, heat, and moisture are almost constant
  with height)
• Thickness typically 1 km varying from 20 m to
  several km deeper with strong solar heating,
  strong winds, rough surface, or upward mean
  vertical motion in the free troposphere.
• Both structure and thickness have a strong
  diurnal cycle.
• Turbulent motions (opposite to laminar flow)
• chaotic swirls rapid chaotic fluctuations in
  winds, temperature, moisture, other mass
• generated mechanically (in the presence of strong
  near surface mean winds), or
• generated thermally (strong solar heating ? high
  buoyancy ? vertical motion)
• (mostly
  daytime, land also common over the oceans)
• ABL clouds fog, fair weather cumulus,
  stratocumulus

               ,
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Potential Temperature
The potential temperature (?) of a parcel of air
at pressure P is the temperature that the parcel
would acquire if adiabatically brought to a
standard reference pressure P0 ( 1000
millibars). where T the current absolute
temperature (in K) of the parcel, R the gas
constant of air, and cp the specific heat
capacity at a constant pressure. See GPC Appendix
C for derivations. ? is a more dynamically
important quantity than T. Under almost all
circumstances, ? increases upwards in the
atmosphere, unlike T which may increase or
decrease. ? is conserved for all dry adiabatic
processes, and as such is an important quantity
in the ABL (which is often very close to being
dry adiabatic). The dry adiabatic lapse rate Gd
g/cp 9.8 C/km ? is a useful measure of the
static stability of the unsaturated atmosphere.
stable, vertical motion is suppressed
unstable, convection is likely
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Stüve diagram (Thermodynamic Diagram)

• Isotherms are straight and vertical, isobars are
  straight and horizontal and dry adiabats are also
  straight and have a 45 degree inclination to the
  left while moist adiabats are curved (see also
  GPC Appendix C, Fig. C.1).
• T20C,
• P1000 mb
• ? ? 20C
• T20C,
• P900 mb
• ? 28.96C
• A parcel with P, T, q ? Td ? q?, RH?, LCL?
  ?q?

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Thermodynamics
http//hyperphysics.phy-astr.gsu.edu/Hbase/heacon.
htmlheacon
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Air Flow and Turbulent Vortices
Air flow can be imagined as a horizontal flow of
numerous rotating eddies, a turbulent vortices of
various sizes, with each eddy having 3D
components, including vertical components as
well. The situation looks chaotic, but vertical
movement of the components can be measured from
the tower.
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Determine Vertical Fluxes
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Reynolds Decomposition and Eddy Covariance
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Reynolds Decomposition and Eddy Covariance
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Bulk Aerodynamic Formulas (Parameterizations)
t ? CDM Ur2 SH cp ? CDH Ur Ts
Ta(zr) LE L ? CDE Ur qs qa(zr) CDN ?
/ ln(zr/z0)2 CDM CDN,M fM(RiB) CDH CDN,H
fH(RiB) CDE CDN,E fE(RiB)
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Global Distribution of Sensible Heat Flux
http//www.cdc.noaa.gov/
13
Global Distribution of Latent Heat Flux
http//www.cdc.noaa.gov/
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Regional Patterns of The Surface Energy Balance
Yuma, AZ energy balance (ly/day) At the other
extreme is Yuma, Arizona, a warm and dry climate.
The most noticeable characteristic of this place
is the lack of latent heat transfer. Though 
ample radiation is available here, there is no
water to evaporate. Nearly all net radiation is
used for sensible heat transfer which explains
the hot dry conditions at Yuma.
West Palm Beach, Fl energy balance (ly/day) West
Palm Beach, Florida  is located in a warm and
moist climate. Latent energy transfer into the
air is greatest during the summer time which is
the wettest period of the year, and when net
radiation is the highest. During the summer,
sensible heat transfer decreases as net radiation
is allocated to evaporation and latent heat
transfer.
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Modeling of The Surface Energy Balance
NCAR CLM http//www.cgd.ucar.edu/tss/clm/ for
global climate modeling and projections NCEP
Noah LSM for numerical weather predictions
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2008 CCSM Distinguished Achievement Award
Niu Yang, 2003, 2006
Yang et al., 1997, 1999
Niu, Yang, et al., 2005
Niu, Yang, et al., 2007
Yang Niu, 2003
Collaborators UT (Z.-L. Yang, G.-Y. Niu, R.E.
Dickinson) NCAR (G.B. Bonan, K. Oleson, D.
Lawrence)
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Noah LSM with hydrological enhancements

Collaborators UT (Z.-L. Yang, G.-Y. Niu, D.
Maidment), NCAR (Fei Chen, Dave Gochis) NCEP
(Ken Mitchell)
Subgrid Disaggregation
Dynamical Routing Methodologies

• fully distributed flow/head
• reservoir levels
• distributed soil moisture
• distributed land/atmo fluxes
• distributed snow depth/SWE

1-D Noah Community Land Surface Model
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Observing The Surface Energy Balance
FLUXNET http//daac.ornl.gov/FLUXNET/ See also
other flux measurement networks (e.g., Ameriflux,
CarboEurope, Fluxnet Canada, and iLEAPS).
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International Programs
GEWEX http//www.gewex.org/ Many others
http//www.gewex.org/links-org.htm