The SCM Experiments at ECMWF

1
The SCM Experiments at ECMWF

• Gisela Seuffert and Pedro Viterbo
• European Centre for Medium Range Weather
  Forecasts

ELDAS Progress Meeting 12./13.12.2002
2
The Goals at ECMWF in ELDAS

• Build a system that complements the use of 2T/2RH
  information to get an optimal estimate of soil
  water assimilating
• - thermal IR heating rates
• - MW brightness temperature
• - precipitation and radiation
• Test, validate amd intercompare that system
• (Single-Column Experiments, comparison with
  measurements)
• Annual soil moisture data base for Europe
  (1.10.1999 31.12.2000)
• ECMWF expects to have a system that can go into
  pre-production by
• the end of ELDAS (2004)

3
Experiment Design
Atm. initial conditions dynamics forcing
from ECMWF reanalysis (ERA40)
Single-column model of the ECMWF NWP model
microwave emissivity model
Observation of precipitation radiation
First guess T2m,RH2m,Tb
Increments (daily)
Soil moisture analysis scheme OI or Extended
Kalman Filter
Observations T2m,RH2m,Tb
Soil moisture
Background error
4
Soil moisture analysis systems

• Optimal Interpolation
• Used in the operational ECMWF-forecast since 1999
  (Douville et al., 2000)
• Fixed statistically derived forecast errors
• Criteria for the applicability of the method
• - atmospheric and soil exceptions
• - corrections when T and RH error are negatively
  correlated

• Extended Kalman Filter
• Used in the operational DWD-
• forecast since 2000 (Hess, 2001)
• Updated forecast errors
• Criteria for the applicability of the method
• - no direct atmospheric exceptions
• - soil exceptions still to be tested
• Changes
• - Assimilation of 2m- T and RH, mw-Tb
• Model forecast operator accounts for water
  transfer between soil layers
• Test adaptive EKF

5
Extended Kalman Filter
Forecast (first guess)
Analysed forecast for new soil moisture at t24h
Comparison with observations T2m,RH2m,Tb
Opt. Soil moisture
t9h
t12h
t15h
t24h
t0
Time
Simulated T2m,RH2m,Tb
Minimization 3 perturbed forecasts for each
state variable
6
Changes to the original algorithm

• Model forecast operator M accounts for water
  transfer between soil layers
• Q-Problem
• 1) Q constant
• - defined by innovation error and size of
  soil moisture increments
• 2) Adpative Kalman Filter (Mayer and Tapleys
  estimator, 1976)

forecast
?j
t
t24
time
?p,j
Perturbed forecast layer i
7
Observations

• Murex
• 1.6 9.10.1997 (1995- 1998)
• Forcing
• SW , (unbiased) LW , precipitation
• Validation
• Soil Moisture, Rnet, H, G, LERnet-H-G, Ts
• Assimilation/Validation
• T2m, RH2m, synthetic mw-Tb
• SGP 97
• 15.6 19.7.1997
• Little Washita site (2) (Central Facility
  site(3))
• Forcing SW , LW , precipitation
• Validation Soil Moisture, Rnet, H, G, LE, Ts
• Assimilation/Validation T2m, RH2m, mw-Tb

8
Correction of downward longwave radiation

• Procedure to correct downward longwave radiation
• Bias
• Height difference between model and observation
• Model error using measurements at Carpentras

9
Comparison of OI-Weights and EKF-Gain matrix
Temperature blue - OI weights green/black EKF
gain matrix
Relative Humidity blue - OI weights green/black
EKF gain matrix

• OI weights and KF gain matrix
• adapt similarly to atmospheric
• conditions
• OI puts more weight on
• RH-observations

10
Soil moisture increments
11
Murex Experiment (1.6- 9.10.1997)
Soil Moisture
Latent Heat Flux
12
T2m error
RH2m error
13
Soil moisture, Ts, Tg (5cm), mw-Tb at 6 LT
14
Soil moisture, Ts, Tg, mw-Tb at 6 LT (Tb every
3rd day)
15
SGP97 (15.6 20.7. 1997)
Soil moisture
Latent Heat Flux
16
Soil moisture, Ts, Tg, mw-Tb at 12 LT
17
Conclusions
Gisela Seuffert

• EKF and OI give nearly similar results
• Assimilation of mw-Tb improves the soil moisture
  simulation
• Assimilation of screen level T, RH and mw-Tb
  gives best results
• - especially when mw-Tb data are not available
  every day
• Assimilation of T, RH and mw-Tb improves either
  soil moisture
• or latent heat flux

18
Plans

• Assimilation aspects
• Minimize the combined errors in prediction of
  soil moisture, latent heat flux and screen level
  observations
• Further mw-Tb assimilation experiments (viewing
  angle, times)
• Assimilation of heating rates
• Technical aspects
• Paper(s) focusing on the
• - new features of assimilation method
• - assimilation of mw-Tb
• - assimilation of heating rates
• Summer 2003 Build production system for the
  annual data base
• End of 2003 Start production