chapter 4 the energy balance of the surface kiehl and trenberth (1997) 1.why the seb? 2.what and...
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Chapter 4 The Energy Balance of The SurfaceChapter 4 The Energy Balance of The Surface
Kiehl and Trenberth (1997)Kiehl and Trenberth (1997)
1.1. Why The SEB?Why The SEB?2.2. What and How? What and How? a.a. SEB components (Rn, SH, LE, G, B, Tskin, SEB components (Rn, SH, LE, G, B, Tskin, εε, , αα, examples) , examples) b.b. ABL (neutral, stable, unstable, Ri, z/L, entrainment, LCL, eddy ABL (neutral, stable, unstable, Ri, z/L, entrainment, LCL, eddy
covariance, bulk formulations, examples) covariance, bulk formulations, examples) c.c. SEB measurementsSEB measurementsd.d. SEB remote sensing SEB remote sensing e.e. SEB modeling (LSMs)SEB modeling (LSMs)f.f. International Programs (GEWEX)International Programs (GEWEX)
The Atmospheric Boundary LayerThe Atmospheric Boundary Layer
ABL = The part of the troposphere that is directly influenced by the presence of the earth’s 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.htm http://apollo.lsc.vsc.edu/classes/met455/notes/section9/1.html
The Atmospheric Boundary LayerThe Atmospheric Boundary Layer1. Definition: ABL = The part of the troposphere that is directly influenced by the presence of
the earth’s surface, and responds to surface forcings with a time scale of about an hour or less.
2. Structure: free atmosphere, entrainment zone, mixed layer (where U, θ, q almost constant with height), surface layer (where vertical fluxes of momentum, heat, and moisture are almost constant with height)
3. 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.
4. Both structure and thickness have a strong diurnal cycle.5. Turbulent motions (opposite to laminar flow)
i. chaotic swirls; rapid chaotic fluctuations in winds, temperature, moisture, other massii. generated mechanically (in the presence of strong near surface mean winds), oriii. generated thermally (strong solar heating high buoyancy vertical motion) (mostly daytime, land; also common over the oceans)
6. ABL clouds: fog, fair weather cumulus, stratocumulus
,
Potential TemperaturePotential Temperature
The potential temperature (θ) 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.
θ is a more dynamically important quantity than T. Under almost all circumstances, θ increases upwards in the atmosphere, unlike T which may increase or decrease. θ 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: Γd = g/cp = 9.8 °C/km
θ is a useful measure of the static stability of the unsaturated atmosphere.
stable, vertical motion is suppressed;
unstable, convection is likely
Stüve diagramStüve 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).
T=20°C,P=1000 mb θ= 20°C
T=20°C, P=900 mb θ= 28.96°C
A parcel with P, T, q Td =? q*=?, RH=?, LCL=? Δq=?
Thermodynamics
http://hyperphysics.phy-astr.gsu.edu/Hbase/heacon.html#heacon
Air Flow and Turbulent VorticesAir 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.
Determine Vertical FluxesDetermine Vertical Fluxes
Reynolds Decomposition and Eddy CovarianceReynolds Decomposition and Eddy Covariance
Reynolds Decomposition and Eddy CovarianceReynolds Decomposition and Eddy Covariance
Bulk Aerodynamic Formulas (Parameterizations)Bulk Aerodynamic Formulas (Parameterizations)
τ = ρ CDM Ur2
SH = cp ρ CDH Ur [Ts – Ta(zr)]
LE = L ρ CDE Ur [qs – qa(zr)]
CDN = [κ / ln(zr/z0)]2
CDM = CDN,M fM(RiB)CDH = CDN,H fH(RiB)CDE = CDN,E fE(RiB)
Global Distribution of Sensible Heat FluxGlobal Distribution of Sensible Heat Flux
http://www.cdc.noaa.gov/
Global Distribution of Latent Heat FluxGlobal Distribution of Latent Heat Flux
http://www.cdc.noaa.gov/
Regional Patterns of The Surface Energy BalanceRegional 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.
Modeling of The Surface Energy BalanceModeling 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
NCAR CLM 3.5Biogeochemistry
Ecosystem DynamicsHydrology
Biogeophysics
Niu, Yang, et al., 2007Niu, Yang, et al., 2005
Yang et al., 1997, 1999Niu & Yang, 2003, 2006
Yang & Niu, 2003
Collaborators: UT (Z.-L. Yang, G.-Y. Niu, R.E. Dickinson); NCAR (G.B. Bonan, K. Oleson, D. Lawrence)
2008 CCSM Distinguished Achievement
Award
Collaborators: UT (Z.-L. Yang, G.-Y. Niu, D. Maidment), NCAR (Fei Chen, Dave Gochis); NCEP (Ken Mitchell)
1-D ‘Noah’ Community 1-D ‘Noah’ Community Land Surface ModelLand Surface Model
Dynamical Routing MethodologiesDynamical Routing Methodologies
Explicit diffusive wave overland flow
Explicit saturatedsubsurface flow
Groundwater discharge, reservoir routing &
Explicit channel routing
• fully distributed flow/head• reservoir levels• distributed soil moisture• distributed land/atmo fluxes• distributed snow depth/SWE
Noah LSM with hydrological enhancements
Observing The Surface Energy BalanceObserving The Surface Energy Balance
FLUXNET http://daac.ornl.gov/FLUXNET/
See also other flux measurement networks (e.g., Ameriflux, CarboEurope, Fluxnet Canada, and iLEAPS).
International ProgramsInternational Programs
GEWEX http://www.gewex.org/
Many others http://www.gewex.org/links-org.htm
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