Using Flux Observations to Improve Land-Atmosphere Modelling:

A One-Dimensional Field Study

Robert Pipunic, Jeffrey Walker & Andrew Western

The University of Melbourne

Cathy Trudinger & Ying Ping Wang

CSIRO Marine and Atmospheric Research

Supported by an Australian Postgraduate Award Scholarship and

University of Melbourne – CSIRO Collaborative Research Support Scheme

Synthetic Twin Experiments

21.2 21.9 0.018 3.0

52.2 37.4 0.0303.7

22.0 20.42.0

74.1 47.8 0.046 3.1

21.4 21.7 0.020 2.9

54.1 38.4 0.032 3.3

25.5 21.43.4

21.8 21.3 0.0201.7

56.6 36.1 0.032 2.4

0.017

0.013

LE (W/m^2) H (W/m^2) Root θ (v/v) Root Tsoil(˚C)

Model Outputs

Sta

cked

RM

SE

fro

m a

ll as

sim

ilati

on

ru

ns

Tskin fortnightly

Tskin 2-daily

θ every 3 days

LE&H fortnightly

LE&H 2-daily

H fortnightly

H 2-daily

LE fortnightly

LE 2-daily

Assimilation Runs

Pipunic et al., 2007. Remote Sensing of Environment, In Press.

Kyeamba Creek Experimental Site

3D sonic anemometer & open path gas analyser for LE & H, 3m above ground: 10Hz measurements, 30min averages recorded

Barometric pressure sensor: 1 reading per hourAir temperature & relative humidity probe, 2m above ground: 30min averages recordedWind direction and speed: 30min averages recordedTipping rain gauge bucket: 30min totals recorded4-way radiometer, incoming & outgoing shortwave & longwave radiation: 30min averages recorded

Below the Ground

30cm

60cm

90cm

8cm

(Not to scale)

CS615 Soil Moisture Probes: Measuring every 30 mins

Soil heat flux plates: 30min averages recorded

5cm10cm2cm

20cm

50cm

100cm

Soil temperature probes: Measuring every 30 mins

CSIRO Biosphere Model (CBM) / CABLE

Long Wave Radiation

Short Wave Radiation

Precipitation

LEH

CO2

G Snow

(Not to scale)

L1L2

L5

L4

L3

L6

Wind

Canopy model (Wang & Leuning, 1998):

• LE, H and CO2 for a ‘sunlit’ and a ‘shaded’ leaf canopy;

• LE and H calculated from both vegetation and bare soil based on fraction of transmitted radiation through canopy.

Six computational soil layers using the soil and snow scheme by Kowalczyk et al. (1994):

• Uniform properties for all layers;• Individual volumetric moisture and

temperature - moisture governed by Richard’s equation.

Ensemble Member Generation

obsnew yyPerturbing meteorological variables:

Random number generated at each time step in series, zero mean

Random number generated once for each ensemble and applied to whole series, zero mean

Air Temperature Ensembles

05

1015202530354045

0 1 2 3Days

Tem

per

atu

re (

Deg

.C)

Ensemble MembersObserved Series

Turner et al., 2007. Remote Sensing of Environment, In Press.

Assimilation Over 1 Year Period (2005)• LE+H assimilated on MODIS timescale – twice a day where SW

radiation is >500Wm-2 (representing no cloud cover).

• Surface soil moisture on SMOS timescale – every 3 days.

0 50 100 150 200 250 300 350

Days

Assimilated LE+H Observations

Assimilated Soil Moisture Oservations

Initial Conditions

04080

120160200240280320

0 5 10 15 20 25 30 35 40 45Initial Soil Moisture (%Vol/Vol)

Dep

th (

cm)

♦ Observed Spin-up

Using spin-up with best available parameters (1 January 2005)

04080

120160200240280320

-5 0 5 10 15 20 25 30 35 40Initial Soil Temperature (Deg. C)

LE and H: Diurnal Results

-1000

100200300400500600700800900

1000

5 6 7 8 9 10

LE

(W

m-2

)

Offline - Spun-upLE ObservedSurface Soil Moisture AssimilationLE+H AssimilationAssimilated LE

-1000

100200300400500600700800900

1000

5 6 7 8 9 10Days

H (

Wm

-2)

H ObservedAssimilated H

LE and H: Daily Average Results

050

100150200250300350400450

0 60 120 180 240 300 360

LE

(W

m-2

)

Offline - Spun-upObservedSurface Soil Moisture AssimilationLE+H Assimilation

050

100150200250300350400450

0 60 120 180 240 300 360Days

H (

Wm

-2)

Root Zone Soil Moisture and Temperature

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0 50 100 150 200 250 300 350Days

So

il M

ois

ture

(V

ol/V

ol)

Offline - Spun-upObserved Root Zone MoistureSurface Soil Moisture AssimilationLE+H Assimilation

0

10

20

30

40

50

0 60 120 180 240 300 360Days

Ro

ot

Zo

ne

Te

mp

era

ture

(D

eg

.C)

Summary of Results

0.29

113.187.6

0.12

140.2103.1

LE (W/m^2) H (W/m^2) Root ZoneSoil Moisture

(Vol/Vol)

Sta

cked

RM

SE

fro

mb

oth

ass

imil

atio

n r

un

s

Surface SoilMoisture

LE+H

Assimilation Runs

Conclusions

• LE and H assimilation results are better than SM results for estimating LE and H, but slightly worse for soil moisture

• The land surface model used exhibits soil moisture and temperature biases when using standard parameters and forcing; this is likely to be typical of most NWP land models

• Temperature and moisture biases need to be accounted for using a bias-aware assimilation approach

www.cahmda3.info Abstracts due: 1 July 2007