Recent Developments of Medium-Range EPS at JMA

Recent Developments of Medium-Range EPS at JMA

Haruki YAMAGUCHI*, Masakazu HIGAKI, and Masayuki KYOUDANumerical Prediction Division, Japan Meteorological Agency, Tokyo,

Japan

1The 4th THORPEX-Asia Science Workshop (31 October 2012)

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) 2

Specification of medium-range EPS at JMA

3

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)

Will be extended to 264 hours by next March

http://tigge.ecmwf.int/models.html

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 size to improve reliability of probabilistic typhoon track forecasts


Operation Planned upgrades

One-week EPS Typhoon EPS One- week EPS

Typhoon EPS

Horizontal resolution

TL319 (~55km) TL479 (~40km)

Vertical levels 60 levels up to 0.1hPa 100 levels up to 0.01hPa

Initial time 12UTC 00,06,12,18UTC 00,12UTC Not changed

Ensemble size 51 11 27 25

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


Experiment A: Impact of enhancing Horizontal resolution


One-week EPS Operation Experiment A

Horizontal resolution TL319 (~55km) TL479 (~40km)

Ensemble size 51 (27 when comparing to experiment)

27

Initial time 12 UTC 12 UTC (00 UTC omitted)

TL319 TL479

Equivalent horizontal grid representing land around Japan

Better resolve Japan archipelago

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)

Sur

face

win

d sp

eed

[m/s

]

west-east section across the typhoon centerSea level pressure [hPa] Surface

wind speed [m/s]

TL959TL479TL319 TL959

TL479TL319deep

strong

Analysis (For this case, forecasts are too strong)

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

Operation (TL319) Experiment (TL479) GSM (JMA’s high-res TL959 forecast)

Observation (For this case, forecasts are too weak)

Pre

cipi

tatio

n [

mm

/24h

r]

Impact in precipitation probability


Operation (TL319)

Experiment (TL479)

Initial time 2012/1/7 12UTC, FT144

Probability of precipitation exceeding 1mm/24hr

DIFF(Experiment-Operation) & Observation

[%]

[%]

[%]

Green dot (event occurred)Black dot (not)

In some cases, there is a difference near border of orographic precipitation

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


0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 24 48 72 96 120 144 168 192 216

Brie

r ski

ll sc

ore

Forecast time [hr]

Operation(M27) Operation(M51) Experiment(M27)

0.020.0220.0240.0260.028

0.030.0320.0340.0360.038

0.04

0 24 48 72 96 120 144 168 192 216

Brie

r sco

re r

elia

blit

y te

rm

Forecast time [hr]


0.05

0.06

0.07

0.08

0.09

0.1

0.11

0.12

0 24 48 72 96 120 144 168 192 216

Brie

r sco

re r

esol

ution

ter

m

Forecast time [hr]


Reliability term of Brier score

Resolution term of Brier score

Brier skill score

Experiment B: Increasing ensemble size of Typhoon EPS


Typhoon EPS Operation Experiment B

Horizontal resolution TL319 (~55km) Not changed

Ensemble size 11 25

Initial time 00,06,12,18 UTC Not changed

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 areas around up to three typhoons

Targeted area over RSMC Tokyo

Impact on increase of ensemble size

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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)

Verification of strike probability

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Verification target: Typhoon EPS operated initial times during 6 Jun 2012 00UTC ~ 5 Aug 00 UTC

Reliability term is improved


Reliability diagrams of strike probability that the center of a typhoon will pass within 120km during the next five days

Operation(11 members)

Experiment(25 members)

Close look to position error of track forecasts

• 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


Verification target: Typhoon EPS operated initial times during 6 Jun 2012 00UTC ~ 5 Aug 00 UTC

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.

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


Recent Developments of Medium-Range EPS at JMA

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