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Recent Developments of Medium-Range EPS at JMA

Recent Developments of Medium-Range EPS at JMA

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Recent Developments of Medium-Range EPS at JMA

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  1. Recent Developments of Medium-Range EPS at JMA Haruki YAMAGUCHI*, Masakazu HIGAKI, and Masayuki KYOUDA Numerical Prediction Division, Japan Meteorological Agency, Tokyo, Japan The 4th THORPEX-Asia Science Workshop (31 October 2012)

  2. Outline • Introduction of One-week EPS and Typhoon EPS of JMA • Experiment A • Impact of enhancing horizontal resolution of forecast model in One-week EPS • Experiment B • Impact of increasing ensemble size in typhoon track forecasts in Typhoon EPS • Summary The 4th THORPEX-Asia Science Workshop (31 October 2012)

  3. Specification of medium-range EPS at JMA Will be extended to 264 hours by next March More detailed information is available at the JMA part of the latest “WMO Technical Progress Report on GDPFS and NWP Research” and the standardized EPS documentation in Excel spreadsheet format at http://tigge.ecmwf.int/models.html The 4th THORPEX-Asia Science Workshop (31 October 2012)

  4. Planned upgrades of the two EPSs • Both EPSs: Enhancing forecast model • Apply several improvements in high-res deterministic forecast GSM, including increase of vertical levels • Increase horizontal resolution for better weather forecast in Japan • One-week EPS: Increasing frequency of operation to two times in a day as almost retaining ensemble size per day to offer forecasters more fresh materials. • Typhoon EPS: Almost doubling ensemble sizeto improve reliability of probabilistic typhoon track forecasts The 4th THORPEX-Asia Science Workshop (31 October 2012)

  5. Experiments • Planned changes are broken down into several small changes and have been examined by multiple experiments. Two of them are introduced. • Experiment A:Enhancing horizontal resolution of One-week EPS to examine impacts in • Reducing “gap” with high-res deterministic GSM • Better orographic effects • Experiment B: Increasing ensemble size of Typhoon EPS to examine impacts in • Improving probabilistic typhoon track forecasts The 4th THORPEX-Asia Science Workshop (31 October 2012)

  6. Experiment A: Impact of enhancing Horizontal resolution Equivalent horizontal grid representing land around Japan TL319 TL479 Better resolve Japan archipelago The 4th THORPEX-Asia Science Workshop (31 October 2012)

  7. Tropical cyclone • Typhoons reproduced in the experiment tend to get closer to those of high-res GSM in the ways that: • The typhoons have deep center with strong wind near the center • Actually they are often too strong compared to analysis Unperturbed member of the EPSs, initial time 27 AUG 2011 12UTC, FT 72 hr Operation(TL319) Experiment (TL479) GSM (JMA’s high-res TL959 forecast) Analysis (For this case, forecasts are too strong) Surface wind speed [m/s] west-east section across the typhoon center Sea level pressure [hPa] Surface wind speed [m/s] TL319 TL959 TL479 TL479 strong TL319 TL959 deep The 4th THORPEX-Asia Science Workshop (31 October 2012)

  8. Winter monsoon • Typical weather with winter monsoon • Upwind orographic precipitation and stripe precipitation pattern in Pacific • Experiments shows finer precipitation pattern • Not so obvious difference of upwind orographic precipitation between operation and experiment Unperturbed member of the EPSs, initial time 23 DEC 2011 12UTC, FT 72 hr GSM (JMA’s high-res TL959 forecast) Observation (For this case, forecasts are too weak) Experiment (TL479) Operation(TL319) Precipitation [mm/24hr] The 4th THORPEX-Asia Science Workshop (31 October 2012)

  9. Impact in precipitation probability In some cases, there is a difference near border of orographic precipitation Operation(TL319) Probability of precipitation exceeding 1mm/24hr [%] DIFF(Experiment-Operation) & Observation [%] Green dot (event occurred) Black dot (not) Experiment (TL479) [%] Initial time 2012/1/7 12UTC, FT144 The 4th THORPEX-Asia Science Workshop (31 October 2012)

  10. Verification of precipitation probability • AMeDAS rain gauge observation on land across Japan, converted 0.5625deg x 0.5625deg verification grid, is compared with forecast • Period: 2012 JAN 3~ FEB 3 12UTC • Brier score of probability of precipitation exceeding 1mm/24hr • Brier skill score is improved by improving both reliability and resolution term. • Score of Experiment is also comparable or superior to that of 51-member Operation Reliability term of Brier score Brier skill score good good Experiment(M27) Resolution term of Brier score Operation(M51) Operation(M27) good The 4th THORPEX-Asia Science Workshop (31 October 2012)

  11. Experiment B: Increasing ensemble size of Typhoon EPS • Typhoon EPS has the following features: • Identical forecast model with One-week EPS • Specialized for Typhoon forecast in RSMC Tokyo • Initial perturbations are composed of singular vectors targeted at RSMC Tokyo and around typhoons like the right figure • High frequency operation (up to 4 per day) but with smaller ensemble size than One-week EPS Targeted area over RSMC Tokyo Targeted areas around up to three typhoons The 4th THORPEX-Asia Science Workshop (31 October 2012)

  12. Impact on increase of ensemble size Operational EPS (11 members) Experiment (25 members) • Ensemble TC tracks of Typhoon “Talas”up to 120 hours derived from the Typhoon EPS (left panel) and an experimental EPS (right panel). • - Initial time is 12UTC 28th August 2011. • - Black lines and color lines indicate the best track and the forecast tracks, respectively. The 4th THORPEX-Asia Science Workshop (31 October 2012)

  13. Verification of strike probability Reliability diagrams of strike probability that the center of a typhoon will pass within 120km during the next five days • Verification target: Typhoon EPS operated initial times during 6 Jun 2012 00UTC ~ 5 Aug 00 UTC Operation (11 members) Experiment (25 members) Reliability term is improved The 4th THORPEX-Asia Science Workshop (31 October 2012) 13

  14. Close look to position error of track forecasts • Verification target: Typhoon EPS operated initial times during 6 Jun 2012 00UTC ~ 5 Aug 00 UTC • There found no significant improvement of ensemble mean track forecasts between operation and experiment. • Common difficulties in the both cases are found: • Too large ensemble spread during earlier forecast time, possibly be deteriorating ensemble mean • Spread seems not to be enough for large error cases during later forecast time Position error of ensemble mean forecast is larger than that of control run. Need to tune amplitude of initial perturbations. For large position error cases, larger spread is desired. The 4th THORPEX-Asia Science Workshop (31 October 2012) 14

  15. Summary • JMA prepares the next upgrade of its two EPSs. Two preliminary experiments are introduced. • Results of the experiment enhancing horizontal resolution of One-week EPS • Expected tendency of resemblance to high-res GSM • The center of typhoons tend to be stronger though they often exceed analysis • Improvement of precipitation probability forecast in winter • Results of the experiment increasing ensemble size of Typhoon EPS • Improvement of reliability of strike probability • Little impact in ensemble mean track forecast. • Regardless of ensemble size, there is a need to tune ensemble spread The 4th THORPEX-Asia Science Workshop (31 October 2012)