Bange, J.

Berger, F.H.

Bernhofer, Ch.

Beyrich, F.

Foken, T.

Hennemuth, B.

Huneke, S.

Kohsiek, W.

Leps, J.P.

Lohse, H.

Lüdi, A.

Mauder, M.

Meijninger, W.M.L.

Mengelkamp, H.T.

Wageningen Yield 

 9.1                   ENERGY AND WATER VAPOR FLUXES OVER A HETEROGENEOUS LAND SURFACE:
THE LITFASS-2003 EXPERIMENT
Frank Beyrich* 1), Jens Bange  4), Franz H. Berger 6),Christian Bernhofer 6) , Thomas Foken 5), Barbara
Hennemuth 2), Sven Huneke 3), Wim Kohsiek 7), Jens-Peter Leps 1), Horst Lohse 3), Andreas Lüdi 9), Matthias
Mauder 5), Wouter Meijninger 8), Heinz-Theo Mengelkamp 3)
1) Meteorological Observatory Lindenberg, German Meteorological Service (DWD), Germany
2) Max-Planck Institute for Meteorology, Hamburg, Germany,
3) Institute for Coastal Research - GKSS Research Centre Geesthacht, Germany
4) Institute for Aerospace Systems, Technical University of Braunschweig, Germany
5) Department of Micrometeorology, University of Bayreuth, Germany
6) Institute for Meteorolgy and Hydrology, Technical University of Dresden, Germany
7) Royal Netherlands Meteorological Institute (KNMI), De Bilt, The Netherlands
8) Wageningen University, Meteorology and Air Quality Group, Wageningen, The Netherlands
9) Institute for Applied Physics, University of Bern, Switzerland
1. Introduction
Land surface - atmosphere interaction processes
play an important role in the energy and water cycle
over a wide magnitude of scales. An adequate
description of these processes in numerical weather
prediction and climate models is  fundamental for a
reliable simulation of near surface weather and
climate conditions. However, considerable deficits
are still to be noticed concerning our understanding
and ability to properly describe these processes
consistently over a variety of scales ranging from
the local patch scale to the regional landscape
scale. This does in particular hold for
heterogeneous land surfaces which are typical for
most regions in Central Europe. To overcome these
deficits, both experimental and modelling activities
have to contribute.
2. The LITFASS-2003 Experiment
In 1995, the German Meteorological Service
(Deutscher Wetterdienst, DWD) has initiated the
LITFASS research project (LITFASS = 'Lindenberg
Inhomogeneous Terrain - Fluxes between
Atmosphere and Surface: a Long-term  Study') in
order to develop and to test a strategy for the
determination of the area-averaged turbulent fluxes of
heat, momentum, and water vapour over a
heterogeneous landscape by combining
measurements and numerical model simulations. The
fluxes shall be representative for a horizontal scale of
about 10 km (while the typical patch scale is between
102 to 103 m) corresponding to the size of a grid cell in
the present operational numerical weather prediction
model of the DWD (Beyrich et al., 2002a, b).
The operational measurement program established at
the Meteorological Observatory Lindenberg (MOL) of
the DWD during the LITFASS project includes the
following components
* Corresponding author address: Frank Beyrich,
Meteorologisches Observatorium Lindenberg, Am
Observatorium 12, D - 15848 Tauche OT Lindenberg
email: frank.beyrich@dwd.de
• a boundary layer field site equipped with a 99m
meteorological tower, a 10m profile mast, a sodar
/ RASS, and measurement systems for the
determination of soil, radiation and turbulence
parameters,
• a network of micrometeorological (flux) stations
operated over different land use classes in the
LITFASS area (grassland, farmland, forest,
water),
• networks of automatically recording rain gauges
and global radiation sensors to characterise the
spatial variability of the main meteorological
forcing parameters (insolation, precipitation), and
• a large-aperture scintillometer (LAS) over a path
length of 4.7 km for the estimation of area-
represen-tative sensible heat fluxes (Beyrich et
al., 2002c).
An aerial view across the heterogeneous landscape
close to the MOL is shown in Figure 1.
Figure1
Aerial view across the LITFASS area with the ABL
field site Falkenberg marked by an arrow
Based on these operational measurements, a
mesoscale boundary layer field experiment
(LITFASS-2003) was organised within the frame of
the EVA_GRIPS project (EVAporation at GRId /
Pixel Scale) of the German Climate Research
Program (DEKLIM) in order to provide a
comprehensive data set on land surface and
boundary layer processes over a heterogeneous
landscape with special focus on evaporation.
LITFASS-2003 took place in the area around the
MOL between May 19, and June 17, 2003. Energy
and water vapor fluxes at different scales were
determined from a combination of ground-based in-
situ and remote sensing instruments, and airborne
measurements. The measurement program
comprised, i.a.:
• thirteen micrometeorological stations operated
over different surfaces representing the major
land use types in the area (forest, water, and
different types of agricultural farmland: grass,
triticale, rape, maize),
• three large aperture optical scintillometers
(LAS) and a microwave scintillometer (MWS)
set up along three different paths over
distances of 3 to 10 km (see Meijninger et al.,
this proceedings),
• synchronised high-resolution (10 seconds
sampling rate) measurements of water vapour
and vertical velocity profiles by a Lidar-/RASS-
combination and by a DIAL/Raman Lidar
combination (see Hennemuth et al., this
proceedings),
• more than 60 flight hours with a turbulence
sonde carried by a Helicopter (the Helipod, see
Zittel et al., this proceedings).
Several orders of magnitudes of sampling domains
and footprint scales were covered by a combination
of these measurement systems which is
summarised in Table 1. The overall set-up of the
measurement systems and the measurement
strategy of the LITFASS-2003 field experiment are
illustrated in Figure 2.
Table 1 Sampling characteristics of the flux
measurements performed during LITFASS-2003
measurement
system
sampling
scale
sampling
domain
footprint
scale
sonic / hygrometer
(~ at tower)
laser scintillometer
remote sensing
LAS
Helipod
10-1 m
10-1 m
102 m
102 m
103 m
100 m
10-1 m
10-1 m
102 m
101 m
103 m
104 m
101..102 m
102..103 m
102..103 m
103..104 m
103..104 m
103..104 m
3. Results
The analysis of the flux measurements comprised
several steps which are illustrated here by using
data from May 25, 2003. Time series of the sensible
and latent heat fluxes measured with the eddy-
covariance systems at each of the 13 surface flux
sites are shown in Figure 3. Data from all sites were
processed by a uniform flux calculation and
correction software (see Foken et al., this
proceedings),  and  the  data  quality  was evaluated
Figure 2
The LITFASS-2003 experimental setup (red circles:
surface flux stations, red lines: LAS paths, blue grid:
Helipod grid flight pattern)
based on the scheme suggested by Foken and
Wichura (1996).
In addition fetch and footprint estimates were
performed in order to sort out non-reliable data. As
can be seen from Figure 3, the local energy and
water vapour flux measurements over the different
types of land use showed significant differences
which were most pronounced between the major
land use classes (forest, low vegetation - farmland,
and water). However, significant differences have
also been found between the different types of
agricultural farmland.
For the different types of agricultural farmland
(cereals, rape, maize, and grassland), flux
composites have then been determined by
averaging the data from all measurements
performed over the same type of crops considering
the actual data quality. In order to account for site
specific differences, a correction factor was derived
for each individual site from the measurements
during time periods where data from all sites of a
given type were available with good quality. This
correction factor represents the ratio of the site-
specific flux when compared to the mean flux of the
relevant crop type. An overall farmland composite
was then constructed in the same way taking into
account the relative occurrence frequency of the
four major crop types in the area. Comparison of the
composites shows (Figure 4), that the highest
farmland evaporation was measured over the rape
fields while the sensible heat flux was highest over
the maize fields which consisted of a considerable
portion of bare soil especially during the first two
weeks of the experiment.
In order to validate this averaging strategy, the
farmland composite (as well as the locally measured
forest fluxes) were compared to area-representative
flux values derived directly from the long-range
scintillometer and from the Helipod measurements
(Figure 5). For the sensible heat flux, good
agreement was found between the scintillometer
and the averages from the surface measurements
characterising the surface types upwind of the
scintillometer paths. Also, the heat flux values
derived from the Helipod measurements along low-
level flight legs over either forest or farmland fit well
into the picture obtained from the surface and
scintillometer data. For the latent heat flux, larger
differences were found between the different types
of measurements. Systematically higher latent heat
fluxes have been derived from the microwave
scintillometer data when compared to the composite
of the eddy covariance measurements, and quite
some scatter has to be noticed in the Helipod fluxes.
Interpretation of these differences will be the subject
of further data analysis.
As a final step, area-averaged fluxes for the whole
LITFASS area (20*20 km2) were computed from the
surface flux data by performing a land-use weighted
average of the flux values representing the different
surface types. Area-averaged surface fluxes were
also determined from the Helipod flight data using
an inverse modelling algorithm (see Bange et al.,
this proceedings). These area-averaged flux values
will further be analysed in relation to numerical
model results and to surface flux estimates from
satellite data. A first example is shown in Figure 6.
Here, the output of the operational run of the NWP
model LM of the DWD and the fluxes estimated
from the NOAA-AVHRR image at around noontime
are presented indicating considerable
overestimation of the latent heat flux both in the
model and from the satellite data.
4. Summary and Outlook
A comprehensive and unique data set on land
surface / atmosphere interaction processes over a
heterogeneous land surface at the meso-γ scale has
been collected during the LITFASS-2003
experiment which was embedded in the operational
measurement program of the MOL. A hierarchy of
instruments and methods was used to derive the
fluxes of energy and water vapor from the local to
the regional scale including eddy-covariance
measurements, scintillometry, ground-based remote
sensing systems and airborne measurements using
the Helipod, a turbulence probe carried by a
helicopter. Analysis of the data revealed a
significant variability of the surface layer fluxes
across the area in dependence on both the land use
and the meteorological forcing conditions. Area-
averaged surface fluxes calculated from the local
measurements by using the tile approach are in
good agreement with area-representative values
directly obtained from the scintillometer and Helipod
measurements. The data collected  during
LITFASS-2003 are now used either as boundary
conditions and forcing data for different kinds of
numerical  models or as a verification data set within
the EVA_GRIPS project. The modeling activities in
EVA_GRIPS comprise 1-dimensional models for off-
line simulations of the soil-vegetation-atmosphere
exchange processes (see Johnsen et al., this
proceedings), 3-dimensional non-hydrostatic
mesoscale models and a large-eddy simulation
model (see Uhlenbrock et al., this proceedings).
Moreover, the data are used to validate retrieval
algorithms for the determination of land surface
parameters and energy fluxes from satellite data.
First comparison with output data from the
operational NWP model runs at DWD showed a
systematic overestimation of the latent heat flux
both in the model and from the satellite data. It
should be remarked that in the operational LM, soil
moisture is a  parameter tuned to optimise the
forecast of the temperature at 2m height which of
course effects the modelled latent heat fluxes.
Further work will also include research versions of
the LM. With this, the EVA_GRIPS project will
contribute to improve the surface processes
parameterisation schemes in NWP and climate
models.
Acknowledgements
The LITFASS-2003 experiment was designed and
performed within the EVA_GRIPS project, funded
from the German Federal Ministry for Education and
Research (BMBF) within the frame of the German
Climate Research Program (DEKLIM) under
contract No. 01LD0103. Part of the measurements
was carried out within the frame of the VERTIKO
project, funded by BMBF within the frame of the
Atmospheric Research Programme AFO-2000
under contract No. 07ATF37.
References
Beyrich, F., S.H. Richter, U. Weisensee, H.-J.
Herzog, H.A.R. de Bruin, W.M.L. Meijninger,
2002a: Fluxes over a heterogeneous land
surface: Results and perspectives of the
LITFASS program, in: AMS: Proc. 15th
Symposium on Boundary Layers and
Turbulence, Wageningen / The Netherlands,
653-654
Beyrich, F.; H.-J. Herzog; J. Neisser, 2002b: The
LITFASS project of DWD and the LITFASS-98
experiment: The project strategy and the
experimental setup. Theor. Appl. Climatol. 73, 3-
18
Beyrich, F.; H.A.R. de Bruin; W.M.L. Meijninger;
J.W. Schipper; H. Lohse, 2002c: Results from
one-year continuous operation of a large-
aperture scintillometer over a heterogeneous
landscape. Boundary-Layer Meteorol. 105, 85-
97
Foken Th., and B. Wichura, 1996: Tools for quality
assessment of surface-based flux measure-
ments. Agricult. Forest Meteorol. 78 83-105
Figure 3
Diurnal cycle of sensible and latent heat fluxes measured at the 13 surface flux sites on May 25, 2003
Figure 4
Diurnal cycle of the composite sensible and latent heat fluxes for the major land use types on May 25, 2003
Figure 5
Diurnal cycle of the sensible and latent heat fluxes over farmland and over forest on May 25, 2003 based on
surface eddy covariance ~, large-aperture scintillometer ~ and Helipod measurements
Figure 6
Diurnal cycle of the sensible and latent heat fluxes over farmland, forest and water and as an average over the
LITFASS area on May 25, 2003 compared to the operational LM output and to a noontime estimate from satellite
data
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HV Forest N4 Grass
N2 Grass FS Water
SS W ater A1 Rye
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A8 Triticale A2 Rape
A7 Rape A9 Rape
A4 Maize A6 M aize
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HV Forest Forest Mean
FS Water Water Composite
Grass Cereals
Maize Rape
Farmland
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Farmland LAS/MWS
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Energy and water vapor fluxes over a heterogeneous land surface: the LITFASS-2003 experiment

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Energy and water vapor fluxes over a heterogeneous land surface: the LITFASS-2003 experiment

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