on the closure of the surface energy balance in highly complex terrain mathias w. rotach, pierluigi...

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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od

eled

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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])