On the Closure of the Surface Energy Balance in
Highly Complex Terrain
Mathias W. Rotach, Pierluigi Calanca, Andreas Weigel, Marco Andretta
Swiss Federal Institute of TechnologyInstitute for Atmospheric and Climate Science
Layout
• Surface energy balance• Data: MAP -Riviera project• Energy balance for a layer• Implications for modeling
MAP-RivieraValley Floor Slope site
Average 15 fair-weather days
Surface Energy balance
NR
G
Ho LvEo
NR-G=Ho+LvEo
Surface Energy balance
• horizontally homogeneous surfaces --> constant turbulent fluxes --> no advection --> closure! [even @ z≠0...]
NR-G=Ho+LvEo
Surface Energy balance
• horizontally homogeneous surfaces --> constant turbulent fluxes --> no advection --> closure! [even @ z≠0...] --> non-closure: measurement error turbulence time scales
NR-G=Ho+LvEo
Surface Energy balance
• horizontally homogeneous surfaces --> constant turbulent fluxes --> no advection --> closure! [even @ z≠0...] --> non-closure: measurement error turbulence time scales
complex terrain...
NR-G=Ho+LvEo
Bellinzona
Biasca Riviera
MAP Riviera project
Lago Maggiore
MAP Riviera project
MAP Riviera Project
MAP-Riviera: Bosco di Sotto
turbulence @ 4 / 16 / 28 m
Local surface: corn, grass
Full radiation comp, precip, profiles,sfc. hydrology
Local slope app. 0.5°
NR
G
Ho LvEozr
H(zr) LvE(zr)
Near-Surface Energy Balance
Near-Surface Energy Balance
NR
G
Ho LvEo
NR-G=Storage+horiz.Adv +vert.Adv
Hr LvEr
z=zr
u Jx
o
zr
dz
w r (J r 1zr
J dzo
zr
)
J cp Lvq
S
G
Corrections
• Sensible Heat flux: --> frequency response (Moore 1986)
--> humidity cross-correlation (Schotanus et al. 1983)• Latent heat flux: --> frequency response (Moore 1986) --> Oxygen (Dijk et al. 2003)
--> WPL-correction (Webb et al. 1980)
Horizontal Advection
Comprovasco
Magadino
u Jx
o
zr
dz
, q
, q
u
J cp Lvq
Riviera
Vertical Advection
, q
, q
zr
w
w r (J r 1zr
J dzo
zr
)
J cp Lvq
Mean vertical wind: from planar fit
Results...
Energy balance terms
NR
H+LE+G
New sum
LE
GH
Average 7 clear sky days
Contributing terms
Sum new terms
Storage air / horiz. advection
Storage soilSum corrections
Vertical advection
Average 7 clear sky days
Vertical advection
ProprtionalDifference in , q....
Vertical advection
Proprtionalmean vertical wind
Energy balance terms
NR
H+LE+G
New sum
LE
GH
Average 7 clear sky days
Conclusions
• Sfc. energy balance in really complex terrain: good to detect processes
• Corrections to turbulent fluxes important• Soil storage term important• Vertical advection!
--> largest--> most uncertain!
Outlook
• If indeed vertical advection is substantial....--> too large a fraction of NR --> H, LE--> cold / dry bias
RAMS simulations - August 25 1999
9.15 UTC 12.08 UTC
observations
model
De Wekker et al. 2003
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del
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od
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del
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edObservedGGGGGGGGGGGGGGGGGGGGGGGGGEEEEEEEEEEEEEEEEEEEEEEEEECCCCCCCCCCCCCCCCCCCCCCCCC
Wheeler FarmNCARAirport All sitesDay: SolidNight: Open
Salt Lake Valley - VTMX
Different models:RAMSMM5ETA
Zhong and Fast 2002
IOP‘s 6,7,10
Outlook
• If indeed vertical advection is substantial....--> too large a fraction of NR --> H, LE--> cold / dry bias
• How to parameterize in numerical models?
Comparisons of observed and simulated sensible heat fluxes
Hydrological modeling – valley floor
Soi
l mo i
stur
e (.
5 m)
ET
und
LE
[m
m/h
]
Pre
cipi
tatio
n [m
m/h
]E
T u
nd L
E [
W/m
2]
Sept 1 1999 Sept 21 1999
ET
und
LE
[W/m
2 ]
time
Observation(Bowen Ratio)
Model (Penman-Monteith)
Eddy Correlation
Hydrological modeling – valley floor
Closed energy balance• Bowen ratio method:
--> if
and
Ho KHz
, LEo Kqq z
KH Kq
Ho
LEoz
q z
Ho NR G11
, LEo NR G1
Planar fitPlot w as a function of (u,v)....
Planar fit on a slope
Common plane vs. local planes
Planar fit vs. Double rotation
(<u
‘w‘>
PF
C -
<u
‘w‘>
DR)/
<u
‘w‘>
DR
(<u
‘w‘>
PF
C -
<u
‘w‘>
PF)/
<u
‘w‘>
PF
C
Andretta et al. (2002)
Finnigan et al. 2003
Energy Balance closure
Data from a ‚flux site‘ in Manaus, Brazil
R 100(H LvE [NR G])