Transcript Allgemein - uni

KENDA status
[email protected]
Deutscher Wetterdienst, D-63067 Offenbach, Germany
Km-scale ENsemble-based Data Assimilation
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priority project in COSMO consortium (CH, D, GR, I, PL, ROM, RU)
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Local Ensemble Transform Kalman Filter (LETKF) ,
(because of its relatively low computational costs)
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provide perturbed initial conditions for COSMO-DE EPS
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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Local Ensemble Transform Kalman Filter
LETKF (Hunt et al., 2007)
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ensemble
mean
forecast
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k perturbed ensemble
forecasts mean fcst.
forecast perturbations
0.9 Pert 1
-0.1 Pert 2
-0.1 Pert 3
-0.1 Pert 4
local
transform
matrix w
Xb
flow-dep background error cov.
Pb
= (k – 1 )
X b (X b )T
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analysis mean
wa
analysis error
covariance
(computed only in
ensemble space)
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analysis
Wa(i)
perturbations
w a ( i )  w a  Wa ( i )
perturbed
analyses
in the (k-1) -dimensional (!) sub-space S spanned by background perturbations :
x  xb  Xb w
set up cost function J(w) in ensemble space,
explicit solution for minimisation (Hunt et al., 2007)
Status KENDA
HErZ LMU, Munich, 6 May 2011
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[email protected]
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LETKF for COSMO :
technical implementation
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analysis step (LETKF) outside COSMO code
 ensemble of independent COSMO runs up to next analysis time
(collecting obs – f.g.  4D -LETKF)
 separate analysis step code, LETKF included in 3DVAR package of DWD
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basically for verification purposes, COSMO obs operators incl. quality control
will be implemented in 3DVAR / LETKF environment
 future: hybrid 3DVAR-EnKF approaches in principle applicable to COSMO
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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LETKF:
status and current work
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deterministic analysis : implemented recently
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ensemble verification yet to be implemented (for upper-air obs by end 2011)
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LETKF not yet included in NUMEX (but should be ‘soon’)
 preliminary LETKF experiments, using Hendrik’s scripts:
– 3-hourly cycles, up to 2 days (7 – 8 Aug. 2009: quiet + convective day)
 near future: 1-hourly / 30-min / 15-min cycles , longer periods
– 32 ensemble members
 near future: ~ 40 ensemble members
– LBC: perturbed (COSMO-SREPS, 3 * 4 members), or unperturbed (C-EU)
 future: perturbed LBC using global GME- / ICON- LETKF
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ensemble lateral BC using GME ensemble from LETKF:
interpolate GME ensemble perturbations to COSMO-DE grid
& add to deterministic COSMO-DE LBC
(our next step ; in NUMEX by Nov. 2011)
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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LETKF:
status and current work
model error : key issue (also for 4DVAR) :
ensemble spread / LETKF is blind to model errors
 lack of ensemble spread  to account for: covariance inflation
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multiplicative
X b   · Xb
(tuning, or adaptive (y – H(x) ~ R + HTPbH))
 works, but large factors required
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additive :
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stochastic physics (revised ECMWF scheme, planned for June 2011, Torrisi, I)
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estimate model error using statistics (Tsyrulnikov, Gorin, RU):
statistical 3DVAR-B  hybrid 3DVAREnKF
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or
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stochastic parameterisation for model error : e = u * M(x) + eadd
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use statistics of distributions of model tendencies and observed tendencies
to estimate parameters u , eadd
(first results encouraging : eadd is reliable , u noisy)
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plan: first practical model error generator available by end of 2011
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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LETKF:
future work: other issues
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localisation (multi-scale DA ?) , update frequency , ensemble size
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non-linear / non-Gaussian aspects, convection initiation (outer loop approaches ?)
MCH: to prepare OSSE with idealised convection, an idealised ensemble setup of
convection will be devised in a master thesis (06/11)
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perturbations of lower BC ?
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how to deal with perturbed lateral BC ?
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technical robustness (must cope with crashes of few ensemble members)
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efficiency
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screen-level obs
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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LETKF (km-scale COSMO) :
current work : new observation types
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radar : radial velocity and (3-D) reflectivity
2 PhD’s at KIT for efficient observation operators mainly (supervised by Uli Blahak)
1st version ready to use by end of Nov. 2011
(Particular issues in LETKF: obs error var + correlations, superobbing + thinning, localisation)
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ground-based GPS slant path delay
(direct use in LETKF , or tomography)
PhD at DWD, job interviews next week
(Particular issue: localisation for (vertically and horizontally) non-local obs )
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cloud information based on satellite and conventional data
Eumetsat Fellow Annika Schomburg at DWD, started March 2011
– derive incomplete analysis of cloud top + cloud base, using conventional obs
(synop, radiosonde, ceilometer) and NWC-SAF cloud products from SEVIRI,
use obs increments of cloud or cloud top / base height or derived humidity
– or use SEVIRI radiances directly
(Issues: non-Gaussian distribution of observation increments, non-linear obs operators, non-local obs)
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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KENDA
thank you for your attention
Status KENDA
HErZ LMU, Munich, 6 May 2011
[email protected]
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