The Surface Energy Balance: Observational Challenges

Dept. of Micrometeorology

The Surface Energy Balance:

Observational Challenges

Land-Atmosphere Interactions at the Regional Scale

Madrid, Oct. 8-10, 2012

THOMAS FOKEN

University of Bayreuth, Germany

Department of Micrometeorology


Content

The energy balance closure problem

The history

Reasons for energy balance closure

Correction of turbulent fluxes

Relevance for modellers

Conclusions


The problem

The net radiation is always larger than the sum of the

turbulent fluxes (sensible and latent) and the ground heat

flux:

Typical residual are:

EHGs QQQQ *

%100...70%100*

s

EHG

Q

QQQ


-500

-400

-300

-200

-100

0

100

200

0 3 6 9 12 15 18 21 24UTC

en

erg

y i

n W

m-2

Sensible heat flux

Latent heat flux

Net radiation

Ground heat flux

Residual

Energy balance closure

Foken and Oncley (1995), Mauder et al. (2006), Oncley et al. (2007), Mauder and Foken (2006), Foken (2008)


The history

First detection of an unclosed energy balance during

experiments like FIFE and KUREX at the end of the 1980s

Problem addressed during an EGS workshop 1994 at

Grenoble/France

Several experiments in the 1990s and overview papers like:

Foken (1998), Wilson et al. (2002), Culf et al. (2004), Foken

(2008), Foken et al. (2012)

Pieces of the puzzle emerge in the 2000s


i. Measurement errors, especially those relating to the eddy-

covariance technique

ii. Different balance layers and scales of diverse measuring

methods, as well as the energy storage

iii. Advection and fluxes due to longer wave lengths

The main reasons for energy balance unclosure


The eddy-covariance

method Direct method with high data

quality, if the method is correctly

applied

University of Bayreuth,

Nam Co site, Tibetan

Plateau, 2009

Applying one of Reynolds’

Postulates

x w + x w = x w ''

and assumption:

w 0

x w + x w = x w ''


Corrections have

no significant

influence on the

closure problem.

© Mauder and Foken(2006)

The eddy-covariance method - Corrections


The transformation of the buoyancy flux into the sensible heat flux and the transformation of the latent heat flux (CO2 flux) due to density fluctuations can impact the flux to some degree but doesn’t significantly influence the closure problem

LITFASS-2003 Experiment, maize, 6 week average

© Mauder and Foken (2006)

The Eddy-Covariance Method - Corrections







The main reasons for energy balance un-closure


Different balance layers and scales of diverse

measuring methods

There is no balance layer !

Measurements cover an energy budget of a volume

© Foken (2008)


Different balance layers and scales of diverse

measuring methods

© Foken (1998)


Energy Storage

The energy storage in the air and in low plants are very small

There is a relevant storage term in the upper soil layer, often

included into the calculation of the ground heat flux

The storage term in high vegetation (forest) cannot be ignored

© Oncley et al. (2007)

© Heusinkveld et al. (2004): In the dessert the energy balance can be closed

© Liebethal and Foken (2007): In the night the energy balance can be closed

© Haverd et al. (2007), Lindroth et al. (2010)







The main reasons for energy balance unclosure


Application of the eddy-covariance method on

fluxes above volume elements –

Generalized eddy-covariance method

Definition of the method: plane surface, homogeneous terrain

Equation for volume element (only w-component shown)

The eddy-covariance method is only one part of the flux

equation!

dzz

w

zwdz

thwF

h

cc

hc

cn

00

''

WPL-correction

Advection (add. terms for horiz. Adv.)

Storage

Eddy-covariance flux

Aubinet et al. (2003), Finnigan et al. (2003), Foken et al. (2012)


Coordinate rotation for zero vertical wind

in complex terrain

Rotation into stream

lines for longer periods

Finnigan et al. (2003)


The Energy Balance closure EXperiment

EBEX-2000 in California

Problems of measuring

devices can be excluded

The energy storage in

plants and soil is low and

can be determined

Advection is possible,

but complicate to measure

Advection cannot explain

the energy balance closure

completely

Oncley et al. (2007)

Oncley et al. (2007), Leuning et al. (2012)


Extension of the averaging period –

The ogive function

Accumulation of the co-spectrum

0

,0,

f

xwxw dffCofOg

0

,0,

f

xwxw dffCofOg

© Foken et al. (2006)

© Desjardins et al. (1989), Oncley et al. (1990)



The long term calculation

Long-term averaging can close the energy balance, the

sensible heat flux is more affected.

© Finnigan et al. (2003),

Mauder and Foken (2006)

In a heterogeneous landscape this is not true for all sites

© Charuchittipan et al. (2012 subm.)



Meso-scale flux

© Finnigan et al. (2003)

Total flux = 0 meso-scale eddy-covariance

Meso-scale flux:

1. To balance the unsteady horizontal flux

divergence and transient changes in source and

storage terms.

2. To carry the low frequency contribution to the

long-term vertical flux.



Meso-scale flux


Rye Grass

Significant structures in the sensible heat flux only over rye.



Meso-scale flux – Wavelet analysis


sensible heat flux latent heat flux

Significant structures can be found only in the sensible heat flux


Secondary circulations found with LES

simulations for the LITFASS-2003 experiment

© Kanda et al. (2004) Inagaki et al. (2006), for LITFASS-2003 Experiment, according to Uhlenbrock et al. (2004)

Foken et al. (2010)

NIMEX-1 (2004)

Experiment

Nigeria

Residual: 0 %

2003/05/30, 12 UTC 2003/06/13, 12 UTC

1.3 zi 1.3 zi


Fluxes from LAS and LES simulations

Fluxes in higher levels (50-100 m) are larger than at the ground

and can probably close the energy balance

© Foken et al. (2010)


Influence of the heterogeneity of the

landscape on the energy balance closure

EBEX-2000

Experiment

U.S.A., CA

Residual: 10-15 %

© Mauder et al. (2007), Stoy et al. (2012 subm.)

LITFASS-2003

Experiment

Germany

Residual: 25-35%

NIMEX-1 (2004)

Experiment

Nigeria

Residual: 0 %

Negev desert

Israel

Heusinkveld, et al. 2004

Residual: 0 %


Conditions of free convection in a

heterogeneous landscape

p1 p2

p1: no horizontal wind, free convection

p2: horizontal wind (about 2 hours after p1)

© Brötz et al. (2012, subm.)


Modelling outcomes

Heterogeneous surfaces

generate additional fluxes -

mosaic meso-models.

LES models can close the

energy balance with Turbulent

Organized Structures (TOS).

Experimental findings

Forest edges generate additional fluxes

Scintillometer measurements nearly close the energy balance

Aircraft measurements close the energy balance

Long integration times of surface measurements close the energy balance

Tower measurements are closed more thoroughly (80-90 %) than surface measurements (70-80 %)

Probably the sensible heat flux is more affected than the latent heat flux

Comparison of the results

© e.g. Schmid and Bünzli (1995), Friedrich (2000)

© Klaassen et al. (2002), Eder et al. (2012 subm.)


Schematic Overview of the Generation of

Secondary Circulations and the Energy

Balance Closure

© Foken (2008)


Landscape scale (2-50 km)

The energy balance is closed!

This can be controlled by: LES and subgrid modelling, scintillometer and aircraft measurements, (integration of surface measurements

over 24 h)

Plot scale (0.1 – 2 km)

The energy balance is not closed!

- except for measurements in a homogeneous landscape

But: EC measurements are accurate for the plot, process studies are possible, MO-theory is valid, Bowen-ration method fails

Probably no scalar similarity

First conclusions


How to correct the energy balance closure ?

Correction according to the Bowen ratio

Correction according to the buoyancy flux

© Twine et al. (2000)



Why is the energy balance closure problem

relevant for modellers?

The energy balance in a model is closed by definition

But:

Climate models must model surface fluxes with high

accuracy

Surface fluxes are necessary for model validation

Surface fluxes are necessary as ground truth for remote

sensing


Two types of Land-surface models

Models which close the

energy balance by iteration

and a uniform surface

temperature

Similar to the energy

balance closure with the

Bowen ratio

e.g. SEWAB

One of the fluxes is

calculated as a residual

Often the ground heat flux is

overestimated

e.g. REMO, TERRA

© Kracher et al. (2009)

© Mengelkamp et al. (1999)

© Jacob and Podzun(1997)

© Steppeler et al. (2003)


Two types of Land-surface models

LITFASS-2003 Experiment, maize, 6 week average

© Kracher et al. (2009)

Difference SEWAB – Measurements

All fluxes were corrected similarly

Difference REMO – Measurements

Overcorrection of the ground heat

flux


Influence on the Monin-Obukhov similarity theory

- sensible heat flux -

Use of Prt in the profile equation or in the universal

function, e.g. in the universal function by Högström (1988)

For latent heat flux use turbulent Schmidt number

Sct ~ Prt

L

zz

T

T

zH

t

*Pr

01Pr2

1

Lz

Lz

Lz

tH

© Yaglom (1977), Högström (1988), Foken (2006)


The Universal Function by Businger et

al. (1971) modified by Högström (1988)

1061

023.1914

1

Lz

Lz

Lz

Lz

Lz

m

108.795.0

026.11195.02

1

Lz

Lz

Lz

Lz

Lz

H

05.1Pr

14.0 t

Prt in the univ. Fkt. ! © Businger et al. (1971), Högström (1988), Jacobson (2005), Foken (2006)


The Turbulent Prandtl Number

• Remark: Even today the accuracy of the

turbulent Prandtl number is only 5-10 %

• No data for the turbulent Schmidt number

• The reason may be the unclosed energy balance

Author 1/Prt

Businger et al. (1971) 1.35

– Correction according to Wieringa (1980) 1.00

– Correction according to Högström (1988) 1.05

Kader & Yaglom (1972) 1.15 – 1.39

Foken (1990) 1.25

Högström (1996) 1.09 0.04

© Foken (2006)


Final conclusion

The problem of the unclosed energy balance is relevant for

experimentators and modellers

Experimental data should be corrected for energy balance

closure

Modellers must be aware about the problem

A revision of universal functions and the turbulent Prandtl

and Schmidt number should be necessary.


References Aubinet M, Heinesch B and Yernaux M (2003) Horizontal and vertical CO2 advection in a sloping forest. Boundary-Layer Meteorol.

108:397-417.

Brötz B, Eigenmann R, Dörnbrack A, Wirth V and Foken T (2012) Valley wind-controlled convective transport in the early-morning

boundary layer above low-mountain terrain. Boundary-Layer Meteorol:to be submitted.

Businger JA, Wyngaard JC, Izumi Y and Bradley EF (1971) Flux-profile relationships in the atmospheric surface layer. J Atmos Sci.

28:181-189.

Charuchittipan D, Babel W, Mauder M, Beyrich F, Leps J-P and Foken T (2012) Extension of the averaging time of the eddy-

covariance measurement and its effect on the energy balance closure Boundary-Layer Meteorol:to be submitted.

Culf AD, Foken T and Gash JHC (2004) The energy balance closure problem. In: Kabat Pet al (eds.), Vegetation, water, humans and

the climate. A new perspective on an interactive system. Springer, Berlin, Heidelberg, 159-166.

Desjardins RL, MacPherson JI, Schuepp PH and Karanja F (1989) An evaluation of aircraft flux measurements of CO2, water vapor

and sensible heat. Boundary-Layer Meteorol. 47:55-69.

Eder F, Serafimovich A and Foken T (2012) Coherent structures at a forest edge: Properties, coupling and impact of secondary

circulations. Boundary-Layer Meteorol:to be submitted.

Finnigan JJ, Clement R, Malhi Y, Leuning R and Cleugh HA (2003) A re-evaluation of long-term flux measurement techniques, Part I:

Averaging and coordinate rotation. Boundary-Layer Meteorol. 107:1-48.

Foken T and Oncley SP (1995) Results of the workshop 'Instrumental and methodical problems of land surface flux measurements'.

Bull Amer Meteorol Soc. 76:1191-1193.

Foken T (1998) Die scheinbar ungeschlossene Energiebilanz am Erdboden - eine Herausforderung an die Experimentelle

Meteorologie. Sitzungsberichte der Leibniz-Sozietät. 24:131-150.

Foken T (2006) 50 years of the Monin-Obukhov similarity theory. Boundary-Layer Meteorol. 119:431-447.

Foken T, Wimmer F, Mauder M, Thomas C and Liebethal C (2006) Some aspects of the energy balance closure problem. Atmos

Chem Phys. 6:4395-4402.

Foken T (2008) The energy balance closure problem - An overview. Ecolog Appl. 18:1351-1367.

Foken T, et al. (2010) Energy balance closure for the LITFASS-2003 experiment. Theor Appl Climat. 101:149-160.


References Foken T, Aubinet M and Leuning R (2012a) The eddy-covarianced method. In: Aubinet Met al (eds.), Eddy Covariance: A Practical

Guide to Measurement and Data Analysis. Springer, Dordrect, Heidelberg, London, New York, 1-19.

Foken T, Leuning R, Oncley SP, Mauder M and Aubinet M (2012b) Corrections and data quality In: Aubinet Met al (eds.), Eddy

Covariance: A Practical Guide to Measurement and Data Analysis. Springer, Dordrecht, Heidelberg, London, New York, 85-131.

Friedrich K, Mölders N and Tetzlaff G (2000) On the influence of surface heterogeneity on the Bowen-ratio: A theoretical case study.

Theor Appl Climat. 65:181-196.

Haverd V, Cuntz M, Leuning R and Keith H (2007) Air and biomass heat storage fluxes in a forest canopy: Calculation within a soil

vegetation atmosphere transfer model. Agric Forest Meteorol. 147(3–4):125-139.

Heusinkveld BG, Jacobs AFG, Holtslag AAM and Berkowicz SM (2004) Surface energy balance closure in an arid region: role of soil

heat flux. Agric Forest Meteorol. 122:21-37.

Högström U (1988) Non-dimensional wind and temperature profiles in the atmospheric surface layer: A re-evaluation. Boundary-

Layer Meteorol. 42:55-78.

Inagaki A, Letzel MO, Raasch S and Kanda M (2006) Impact of surface heterogeneity on energy balance: A study using LES. J

Meteor Soc Japan. 84:187-198.

Jacob D and Podzun R (1997) Sensitivity Studies with the regional climate model REMO. Meteorol Atmos Phys. 63:119-129.

Jacobson MZ (2005) Fundamentals of atmospheric modelling. Cambridge University Press, Cambridge, 813 pp.

Kanda M, Inagaki A, Letzel MO, Raasch S and Watanabe T (2004) LES study of the energy imbalance problem with eddy

covariance fluxes. Boundary-Layer Meteorol. 110:381-404.

Klaassen W, van Breugel PB, Moors EJ and Nieveen JP (2002) Increased heat fluxes near a forest edge. Theor Appl Climat.

72:231-243.

Kracher D, Mengelkamp H-T and Foken T (2009) The residual of the energy balance closure and its Influence on the results of three

SVAT models. Meteorol Z. 18:647-661.

Leuning R, van Gorsel E, Massman WJ and Isaac PR (2012) Reflections on the surface energy imbalance problem. Agric Forest

Meteorol. 156:65-74.

Liebethal C and Foken T (2007) Evaluation of six parameterization approaches for the ground heat flux. Theor Appl Climat. 88:43-

56.


References

Lindroth A, Mölder M and Lagergren F (2010) Heat storage in forest biomass improves energy balance closure. Biogeosciences.

7(1):301-313.

Mauder M and Foken T (2006) Impact of post-field data processing on eddy covariance flux estimates and energy balance closure.

Meteorol Z. 15:597-609.

Mauder M, Liebethal C, Göckede M, Leps J-P, Beyrich F and Foken T (2006) Processing and quality control of flux data during

LITFASS-2003. Boundary-Layer Meteorol. 121:67-88.

Mauder M, Jegede OO, Okogbue EC, Wimmer F and Foken T (2007) Surface energy flux measurements at a tropical site in West-

Africa during the transition from dry to wet season. Theor Appl Climat. 89:171-183.

Mengelkamp H-T, Warrach K and Raschke E (1999) SEWAB a parameterization of the surface energy and water balance for

atmospheric and hydrologic models. Adv Water Res. 23:165-175.

Oncley SP, Businger JA, Itsweire EC, Friehe CA, LaRue JC and Chang SS (1990) Surface layer profiles and turbulence

measurements over uniform land under near-neutral conditions. 9th Symposium on Boundary Layer and Turbulence, Roskilde,

Denmark, April 30 - May 3, 1990 1990. Am. Meteorol. Soc., pp. 237-240.

Oncley SP, et al. (2007) The energy balance experiment EBEX-2000, Part I: Overview and energy balance. Boundary-Layer

Meteorol. 123:1-28.

Schmid HP and Bünzli D (1995) The influence of the surface texture on the effective roughness length. Quart J Roy Meteorol Soc.

121:1-21.

Steppeler J, Doms G, Schättler U, Bitzer HW, Gassmann A, Damrath U and Gregoric G (2003) Meso-gamma scale forecast using

the non-hydrostatic model LM. Meteorol Atmos Phys. 82:75-96.

Stoy PC, et al. (2012) A data-driven analysis of energy balance closure across FLUXNET research sites: The role of landscape-

scale heterogeneity. Agric Forest Meteorol:submitted.

Twine TE, Kustas WP, Norman JM, Cook DR, Houser PR, Meyers TP, Prueger JH, Starks PJ and Wesely ML (2000) Correcting

eddy-covariance flux underestimates over a grassland. Agric Forest Meteorol. 103:279-300.

Uhlenbrock J, Raasch S, Hennemuth B, Zittel P and Meijninger WML (2004) Effects of land surface heterogeneities on the boundary

layer structure and turbulence during LITFASS-2003: Large-eddy simulations in comparison with turbulence measurements. 6th

symposium on boundary layers and turbulence, Portland (Maine), 9-13 August 2004 2004. Am. Meteorol. Soc., p. paper 9.3.

Wilson KB, et al. (2002) Energy balance closure at FLUXNET sites. Agric Forest Meteorol. 113:223-234.

Yaglom AM (1977) Comments on wind and temperature flux-profile relationships. Boundary-Layer Meteorol. 11:89-102.

The Surface Energy Balance: Observational Challenges

Documents