Transcript Christoph Schraff

Introduction to KENDA as COSMO Priority Project
Christoph Schraff
Deutscher Wetterdienst, D-63067 Offenbach, Germany
KENDA: Km-scale ENsemble-based Data Assimilation
•
Motivation, implementation, status
•
Current & future work
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
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Motivation : Why develop
Ensemble-Based Data Assimilation ?
convection-permitting NWP:
after ‘few’ hours, a forecast of convection is a long-term forecast
 deliver probabilistic (pdf) rather than deterministic forecast
 need ensemble forecast and data assimilation system
(strategic aims in COSMO)
 forecast component: COSMO-DE EPS
developed & operational at DWD
perturbations:
LBC
+
IC
+
physics
perturb.
GME, IFS, GFS, GSM
 ensemble-based data assimilation component missing & required

replace current nudging-based DA by state-of-the-art DA with flow-dependent B
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
Motivation : Why develop
Ensemble-Based Data Assimilation ?
 data assimilation: priority project within COSMO consortium
Km-scale ENsemble-based Data Assimilation (KENDA):
Germany
Greece
Italy
Poland
Romania
Russia
Switzerland

similar
configurations
x = 1 – 3 km ~ 2016 : x  2 km , LETKF

Local Ensemble Transform Kalman Filter (LETKF, Hunt et al., 2007) ,
(because of its relatively low computational costs)
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
3
LETKF (km-scale COSMO) :
implementation
•
analysis step (LETKF) outside COSMO code
 ensemble of COSMO runs, collecting obs – f.g.  4D -LETKF
 separate analysis step code, LETKF included in 3DVAR package of DWD
ensemble
K
deterministic
•
analysis for a deterministic forecast run : use Kalman Gain K of analysis mean
xA = xB + K [yo – H(xB)]
 deterministic run must use same set of observations as the ensemble system !
 deterministic run may have higher resolution (not optimal if deterministic f.g. deviates
strongly from ensemble mean f.g.)
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
Lateral BC /
other LETKF implementations
•
perturbed lateral BC :
(or at DWD)
IFS EPS (MCH, ARPA-SIM)
hybrid EnVar for ICON (GME)
variational formulation
(Buehner et al 2005)
high resolution
deterministic
analysis
lower resolution
analysis
ensemble
(40 members)
•
CNMCA (Lucio Torrisi et al.) : LETKF for 10-km COSMO operational
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
implementation of LETKF features
in KENDA
main development of LETKF at DWD (Hendrik Reich , Andreas Rhodin),
main implemented features:
•
adaptive multiplicative covariance inflation (based on Desroziers statistics)
•
adaptive estimation of obs errors in obs space
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adaptive estimation of obs errors in ensemble space (to account for limited Nens)
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adaptive localisation to keep effective Nobs constant (to account for limited Nens)
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multi-step analysis
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
implementation & LETKF tests
(so far using TEMP, aircraft, surface, wind profiler)
•
DWD:
 stand-alone scripts for 2-day period: many LETKF tests, e.g. adaptive methods
 LETKF in operational experimentation system NUMEX  slow (archive)
 ‘BACY’ (basic cycling scripting environment for KENDA, Hendrik Reich):
• fast (speed: DA with BACY ~ 1 – 2, i.e. ~ 5 – 10 times faster than with NUMEX)
• largely portable (if obs / GME fields provided)
• automatic plotting suite
• model equivalent calculation (MEC) from forecasts for input to verification
 potential: tool to ease collaboration with academia
•
scripting environments for LETKF DA cycle also at
 MeteoSwiss: 1-hourly LETKF DA cycle for 1 month using conventional obs
 ARPA-SIM: first tests, setting up OSSE (Chiara Marsigli)
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
KENDA :
main short-term goal
Main aim: reach operationability in (mid/end) 2015
•system complete (e.g. ana + perturb surface / soil) + robust + efficient
•quality KENDA ≥ quality nudging-based opr. DA (incl. LHN)
(deterministic)
(using similar obs set)
•additional: provide IC perturbations for EPS
evaluation of EPS:
•
EPS: how to use KENDA IC perturbations for EPS (COSMO-DE-EPS)
(PP COTEKINO / Richard Keane, DWD)
replace or rather combine with current IC perturbations
 HErZ LMU: structure & impact of KENDA IC perturbations (Florian Harnisch)
•
Diagnostics: FSO (forecast sensitivity of observations) (Matthias Sommer, LMU)
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
KENDA :
•
short-term tasks
general testing, tuning, optimization of LETKF setup
 specification of observation errors
 use of adaptive methods (localisation, cov. inflation, R in ensemble space),
 multi-step and multi-scale analysis with different obs / localisation scales
 ensemble size (40 ?),
 update frequency at ?
RUC 1 hr  at  15 min ! (high-res. obs)
non-linearity vs. noise / lack of spread / 4D property ?
•
inclusion of additive covariance inflation,
probably using self-evolving perturbations (Lucio Torrisi, CNMCA)
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testing SPPT in DA cycle, possibly also perturbed physics parameters
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inclusion of LHN (latent heat nudging) (as long as reflectivity not ready for use)
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robustness: create new ensemble members, if few crash
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
9
Extended Use of Observations (1)
Aim:
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(implementation,) forecast improvements from using these observations
3D radar radial velocity
Complete obs operator and efficient approximations suitable for DA developed,
thinning and superobbing strategies implemented, preliminary DA cycles
Yuefei Zeng, Uli Blahak (DWD)
(Status of Y. Zeng after June 2014 or other resources at DWD unclear)
•
3D radar reflectivity (direct use)
Complete obs operator and efficient approximations suitable for DA developed,
thinning and superobbing strategies implemented, preliminary DA cycles
Virginia Poli, Tiziana Paccagnella (ARPA-SIM);
Klaus Stephan (DWD), Theresa Bick (U. Bonn)
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
10
Extended Use of Observations (2)
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GPS Slant Path Delay
Obs operators (incl. ray tracer) implemented in DWD global 3DVar;
Aim: implement complete and efficient obs operator in COSMO by end of 2014
Michael Bender ; Erdem Altunac (tomography) (DWD)
No resources available yet after 2014 for use in LETKF
(challenge to use horizontally + vertically non-local obs in LETKF)
•
Cloud Top Height (CTH) derived from Meteosat SEVIRI
Fully implemented, single-obs experiments, cycled DA with dense obs for low-stratus cases
Annika Schomburg (DWD, talk on Monday)
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Direct use of SEVIRI IR window channels in view of assimilating cloud info
Obs operator (RTTOV) + data flow implemented, next monitoring + DA tests
Africa Perianez , DWD, until Feb. 2015, no resources yet thereafter
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Exploratory: SEVIRI VIS/NIR window channels (Leonhard Scheck. LMU)
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
11
Extended Use of Observations (3) :
Future
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Mode-S (high-resolution) wind and temperature data (from aircraft)
and application to high-res airport model COSMO-MUC (with radar data)
Heiner Lange, Tijana Janjic-Pfander (HErZ LMU)
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Screen-level observations (T-2m, q-2m, uv-10m)
(C. Schraff, DWD)
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(+ Master Thesis at MeteoSwiss on station selection)
Direct use of SEVIRI WV channels (for T, qv; for cloud info; linked to IR window)
Great interest by HErZ-LMU for a project, starting 2015
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
12
thank you for your attention
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
13
LETKF for km-scale COSMO :
method
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implementation following Hunt et al., 2007
•
basic idea: perform analysis in the space of the ensemble perturbations
– computationally efficient, but also restricts corrections to
subspace spanned by the ensemble
– explicit localization (doing separate analysis at every grid point,
select only obs in vicinity and scale R-1)
– analysis ensemble members
are locally linear combinations
of first guess ensemble members
forecast
members
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
14
KENDA :
Analysis & Perturbation
of Lower Boundary Fields
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Snow cover and depth, idea:
apply snow analysis independently to ensemble members (with perturbed obs ?)
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Sea surface temperature (SST), idea: add perturbations to deterministic analysis
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Soil moisture (soil temperature) perturbations only: as in EPS (COTEKINO)
Longer-term additional tasks
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Soil moisture (soil temperature) analysis, by using screen-level obs ;
2 ideas:
 add 1 analysis level in LETKF for the soil, and
apply strong localization for calculating the transform matrix for this level
 use the ensemble in current stand-alone variational SMA (perturbations ?)
•
Soil moisture analysis (+ perturbations) using satellite soil moisture data in LETKF
Eumetsat fellowship at CNMCA
Introduction to KENDA
KENDA Mini-Workshop., Munich, 28 Feb. 2014
[email protected]
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