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Development of a LAM ensemble for the
2014 Winter Olympic Games
Andrea Montani, C. Marsigli, T. Paccagnella
ARPA Emilia-Romagna Servizio IdroMeteoClima, Bologna (I)
ServizioIdroMeteoClima
COSMO meetingLugano, 10-13 September 2012
A.Montani; The COSMO-LEPS system.
Outline
• Introduction to COSMO-LEPS system: methodology and implementation.
• Limited-area ensemble activity for FROST-2014: relocation of COSMO-LEPS: COSMO-FRost-EPS.
• Performance of COSMO-FROST-EPS: time-series verification using SYNOP reports and comparison
against ECMWF;
case-study assessment;
• Conclusions and open issues.
A.Montani; The COSMO-LEPS system.
COSMO-LEPS (developed at ARPA-SIMC)
• What is it?It is a Limited-area Ensemble Prediction System (LEPS),
based on COSMO-model and implemented within COSMO (COnsortium for Small-scale Modelling, including Germany, Greece, Italy, Poland, Romania, Russia, Switzerland).
• Why?It was developed to combine the advantages of global-
model ensembles with the high-resolution details gained by the LAMs, so as to identify the possible occurrence of high-impact and localised weather events (heavy rainfall, strong winds, temperature anomalies, snowfall, …)
generation of COSMO-LEPS to improve the forecast of high-
impact weather in the short and early-medium range.
Dim
2
Initial conditions Dim 1
Dim
2
Possible evolution scenarios
Dim 1 Initial conditions
ensemble size reduction
Cluster members chosen as representative members (RMs)
LAM integrations driven byRMs
LAM scenario
LAM scenario
LAM scenario
COSMO-LEPS methodologyCOSMO-LEPS methodology
A.Montani; The COSMO-LEPS system.
Outline
• Limited-area ensemble activity for FROST-2014: relocation of COSMO-LEPS: COSMO-FRost-EPS.
• As for Sochi-2014 Winter Olympics, Roshydromet is organizing a blended RDP/FDP (Research and Development Project / Forecast Demonstration Project) under the auspices of WMO: FROST-2014 (Forecasting and Research: the Olympic Sochi Testbed; http://frost2014.meteoinfo.ru).
A.Montani; The COSMO-LEPS system.
COSMO activities for FROST-2014COSMO is performing a number of activities related to FROST-2014 WWRP
RDP/FDP, coordinated in the framework of the Priority Project CORSO:
a) deterministic forecasting,
b) probabilistic forecasting:
b1) FDP initiatives (COSMO-FROST-EPS: relocation of COSMO-LEPS over the Sochi area),
b2) RDP initiatives (development of a convective-scale ensemble system for the Sochi area),
c) post-processing and product generation,
d) verification (development of VERSUS software for probabilistic verification).
Relocation of COSMO-LEPS system over the Sochi area so as to provide:
• probabilistic forecasting at high resolution for the Olympic competitions,
• support to the deterministic forecasting,
• initial and boundary conditions for the development of a convective-resolving EPS.
A.Montani; The COSMO-LEPS system.
Main milestones of COSMO-FROST-EPS
• 11/3/2011. Nothing present.
• 2/5/2011. Submission of a new ECMWF Special Project (Title: “Implementation of a limited-area ensemble prediction system for Sochi Olympic Games”; Project investigators: Majewski, Montani, Steiner; duration: 3 years) for provision of computer time to run the system on ECMWF super-computers;
• 5-9/9/2011. Discussion during the COSMO meeting about the system set-up;
• 6/12/2011. Approval of the Special Project by ECMWF Council;
• 6-9/9/2011. Visit of Russian colleagues at ARPA-SIMC to define specifics of the new ensemble system;
• 19/12/2011. Beginning of provision of COSMO-FROST-EPS products on a daily basis.
A.Montani; The COSMO-LEPS system.
COSMO-FROST-EPS @ ECMWF: present status
d+3d+3dd d+2d+2d+1d+1
ECMWF EPS
clustering interval
Cluster Analysis and RM identificationCluster Analysis and RM identification
4 variables
Z U V Q
3 levels
500 700 850 hPa
2 time steps
Cluster Analysis and RM identificationCluster Analysis and RM identification
Black-Sea area
Complete Linkage
10 Representative Members driving the 10
COSMO-model integrations (weighted according to the cluster
populations)
employing either Tiedtke or Kain-Fristch
convection scheme (randomly choosen)
+perturbations in
turbulence scheme and in physical
parameterisations
clustering area
• Δx ~ 7 km; 40 ML; fc+72h;• initial time: 00/12 UTC;• At the moment, computer time
(~ 2 million BUs for 2012) is provided by an ECMWF Special Project;
• suite managed by ARPA-SIMC; • contributions from ECMWF
member states could be needed in the future.
Integration Domain
A.Montani; The COSMO-LEPS system.
Disseminated products
All post-processing is done using with COSMO-software fieldextra:
probability fields for the exceedance of thresholds for surface fields;
ensemble mean and ensemble standard deviation for some fields;
individual ensemble members for the generation of point-forecasts;
hourly boundary conditions (from fc+0h to fc+48h) for convective-resolving ensemble (RDP part).
10 perturbed COSMO-model runs (ICs and BCs from 10 selected EPS members): start at 00UTC and 12UTC; t = 72h;
1 deterministic run (ICs and BCs from the deterministic ECMWF forecast) to “join” deterministic and probabilistic approaches: start at 00UTC and 12UTC; t = 72h;
A.Montani; The COSMO-LEPS system.
Outline
• Performance of COSMO-FROST-EPS:verification using SYNOP reports and comparison against ECMWF-EPS;
case-study assessment;
A.Montani; The COSMO-LEPS system.
COSMO-FROST-EPS vs ECMWF-EPS
Main features of verification:
variable: 12h cumulated precip (18-06, 06-18
UTC);
period : from Jan 2012 to Mar 2012;
region: 40-50N, 35-45 (SOCHIDOM);
method: nearest grid point; no-weighted
fcst;
obs: synop reports (about 60
stations/day);
fcst ranges: 6-18h, 18-30h, 30-42h, 42-54h, 54-66h;
thresholds: 1, 5, 10, 15, 25, 50 mm/12h;
scores: ROC area, BSS, RPSS, Outliers, …
systems:
- COSMO-FROST-EPS (10m, 7 km, 40 ML)
- ECMWF-EPS (51m, 25 km, 62 ML)
“Large-scale” verification tends to smooth out differences between higher and lower resolution systems ECMWF-EPS should be favoured.
A.Montani; The COSMO-LEPS system.
Impact of higher resolution
-40
500010 300020001000500100
ECMWF-EPS orography (25 km)
COSMO-FROST-EPS orography (7 km)
7 km still not enough to resolve some scale-scale features
need of statistical post-processing to downscale the information
A.Montani; The COSMO-LEPS system.
ROC area Area under the curve in the HIT rate vs FAR diagram; the higher, the better … Valuable forecast systems have ROC area values > 0.6. Consider the event: 12-hour precipitation exceeding 10 mmConsider the event: 12-hour precipitation exceeding 10 mm
COSMO-FROST-EPS outperforms ECMWF-EPS for all forecast ranges.
12-hour cycle of the score for both systems, which better predict precipitation occurring during daytime (6-18Z).
ROC area values show little dependence on the threshold (not shown).These results need to be confirmed over higher-resolution observational networks.
A.Montani; The COSMO-LEPS system.
Brier Skill Score BSS is written as 1-BS/BSref. Sample climate is the reference system. Useful forecast systems if
BSS > 0. BS is equivalent to MSE for deterministic forecast. BS measures the mean squared difference between forecast and observation in probability
space.
Lower threshold: COSMO-FROST-EPS wins for all forecast ranges.
Higher thresholds: similar performance of the two systems, but fewer obs are available.
Performance of the systems shown for 2 events:• total precipitation exceeding 1 mm in 12 hours
(dashed lines),• total precipitation exceeding 5 mm in 12 hours (solid
lines).
A.Montani; The COSMO-LEPS system.
Ranked Probability Skill Score
BSS “cumulated” over all thresholds. RPSS is written as 1-RPS/RPSref. Sample climate is the reference system. RPS is the extension of the Brier Score to the multi-event situation.
Useful forecast systems for RPSS > 0. RPSS depends on the ensemble size and penalises small ensemble sizes. Consider debiased RPSS: RPSSD = 1 –(RPS/(RPSref + RPSref /N))
In either case (RPSS or RPSSD) COSMO-FROST-EPS has higher scores than ECMWF-EPS for all forecast ranges, despite the lower ensemble size.
RPSS
RPSS
D
A.Montani; The COSMO-LEPS system.
Outliers How many times the analysis is out of the forecast interval spanned by the ensemble members. … the lower the better … In a “well-constructed” ensemble system of N members, the percentage of outliers should
asymptotically approach its theoretical values (= 2/N+1).
COSMO-FROST-EPS has fewer outliers than ECMWF-EPS, especially for shorter forecast ranges.
COSMO-FROST-EPS approaches quickly the theoretical limit; ECMWF-EPS is away from its limit.
A.Montani; The COSMO-LEPS system.
Case-study assessment
1. Heavy precipitation event: snowfall started on 31 January, at 00UTC in the mountains and at 3UTC on the coast. Snowfall lasted 2 days (31 Jan and 1 Feb). In the first day, 18 cm of snow in Sochi, 5 cm in Adler.
2. Foehn event: started on 3 February in the evening (local time) and lasted until 6 February.
Sochi local time = GMT + 4 hours
GMT = Sochi local time – 4 hours
A.Montani; The COSMO-LEPS system.
Probability maps of tp > 20 mm eq water / 24h
All maps verify on 1 Feb 2012, 12UTC
(4pm local time)
IC: 31/1, 00UTC +12-36h
IC: 30/1, 00UTC +36-60h IC: 30/1, 12UTC +24-48h
A.Montani; The COSMO-LEPS system.
• The new COSMO-based ensemble system over the Sochi-area (COSMO-FROST-EPS) was developed, implemented and runs on a daily basis.
• Preliminary verification results indicate the added value of the system with respect to ECMWF-EPS; positive results are confirmed also for case-study analysis.
• 7 km not enough to resolve some small-scale features:
– statistical post-processing to downscale the information FDP?
– dynamical downscaling to generate convective-resolving EPS RDP?
Conclusions and open issues
• COSMO-FROST-EPS is running throughout 2012 (and not only for 6 months), thanks to the Swiss contribution.
• Improve dissemination:
– develop new products “on demand” (in the future “multi-model” products?);
– produce meteograms and/or xml output files,
– Concentrate on issues related to data format / grid / ...
• Improve probabilistic verification:
– COSMO-software VERSUS is being developed to address probabilistic verification,
– need of good-quality observations at high resolution.
A.Montani; The COSMO-LEPS system.
Important ingredients
1. Provide reasonable “numbers”. addressed
2. Develop experience with probabilities.
3. Feedback on the top-priority products. being addressed
4. Snow analysis.
5. Soil-field initialisation.
6. Observations to assess the quality of the system. . being addressed
7. Computer time. addressed
8. Timeliness in product delivery. addressed
9. …
anything to add/remove?
A.Montani; The COSMO-LEPS system.
Thank you !