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TRANSCRIPT
Experimental Extended Range GEFS
Malaquías Peña, Dingchen Hou, Dick Wobus, YuejianZhu Acknowledgment: EMC’s Ensemble Group, EMC’s Global
C&W Modeling Branch
10 Jan 2014 WMO InternaTonal Conference on Subseasonal to Seasonal PredicTon
Global operaTonal ensemble predicTon systems at NCEP
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CFSv2 GEFS
Coupled Yes Atmos-‐Land
Ensemble size 16 80
ResoluTon T126L64 T254L42
Year of operaTon 2011 2012
Ensemble GeneraTon Lagged ETR
Community served Climate Weather
Hindcast CFSRR (Saha et al) ESRL (Hamill et al)
CFS -‐> NMME, IMME GEFS -‐> NAEFS, TIGGE
Both use the GFS as the Atmospheric component
Historical RPSS for GEFS
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2005 2010
• GEFS constantly improving: I.C., higher resoluTon, GFS, perturbaTon methods • GEFS currently outperforms climatology beyond 16 days; slowly approaching to zero
20 Member Ensemble every 6h
Befer than predicTng climatology
ConTnuos Rank Probability Score
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QuanTfies the distance between two staTsTcal objects, which can be two probability distribuTons or samples; or the distance between one point and a distribuTon
CRPS = 1Cases
Fifcst (x)−Fi
obs (x)"# $%−∞
∞
∫i=1
Cases
∑2
dx
CRPSS = (C −CRPS) /C
AC score CRPSS
WH Time Series of Mag(RMM1, RMM2) WH Time Series of Mag(RMM1, RMM2)
From Yuejian Zhu From Yuejian Zhu
10-‐day lead skill and the MJO
Lingering predicTon skill beyond 2 weeks?
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Courtesy of Qin Zhang (CPC)
• GEFS in operaTons in 2007 • T120L42 • AC > 0.5 at around 19 days for the
two MJO leading modes • Decaying average BC in solid line;
CFSv1 in grey dashed lines • The period coincided with a period
of high amplitude of the MJO • Does seem to have value here.
Cheers to the GFS developers! • Plan to use it in the NAEFS project
Can this good skill be reproduced for other periods?
… or Beginner’s Luck? AC of RMM1 and RMM2
Experimental Setup • GEFS runs out to 1080h (45 days) Three forecast segments:
High ResoluTon: T254L42; 00h to 192h (1-‐8 days) Low ResoluTon: T190L42; 192h to 384h (+8 to 16 days)
Extended ResoluTon: T126L42; 384h to 1080h (45 days)
• Daily runs iniTalized at 00Z, no cycling • First two segments same as operaTonal GEFS and ESRL’s Reforecast
• Last segment has addiTonal 10% computaTonal cost to current GEFS
• Hybrid EnKF-‐3DVar iniTal condiTons
WH-‐ MJO Forecast AC Skill
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Courtesy of Qin Zhang (CPC)
Strong Case GEFS Ensemble Mean Raw
Compare AC at lead 0
WH-‐ MJO Forecast Skill
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Courtesy of Qin Zhang (CPC)
Weak Case GEFS Ensemble Mean Raw
We don’t expect the EGEFS as it is now to be a good predicTon model when MJO is weak
Lagged forecasts
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OperaTonal GEFS Experimental GEFS
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Forecast Lead (days) Forecast Lead (days)
GEFS Reforecast
• Produced at ESRL (Hamill et al 2012) • ETR, only 00 UTC, 10 members+control. • 6h cycle was preserved –cycling only 10 membs • StochasTc tendency same as operaTonal • ResoluTon. 1-‐8 days: T254L42 (~40 km at 40 lat) • +8 to 16: T190L42 (54 km at 40 lat) • 29yrs: Dec 1984-‐Nov 2012
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Several deficiencies reported
Under-‐dispersive MJO (The reforecast has 6 members only) 23
Hamill and Kiladis 2013
Expected GEFS upgrades (while a suitable coupled GFS is available)
• Higher resoluTon: T574L42 • EnKF based 3D mask perturbaTons • Surface perturbaTons at iniTal Tme • Tuning of stochasTc perturbaTon parameters • RealisTc evolving (two-‐Ter) SSTs
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PrioriTes and Challenges • AccounTng for model uncertainty properly in ensemble predicTons of extended ranges
• Understanding the predictability of the S2S and sensiTvity to surface perturbaTons
• Assess the benefit of reforecast at leads beyond 2 weeks
• Analyze error growth: systemaTc error growth to opTmize resources to carry on new reforecasts datasets; Phase versus amplitude error
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Concluding Remarks • An extended GEFS is in the preparaTon phase • The EGEFS is intended as a benchmark for a possible coupled versions GEFS.
• The EGEFS does not affect the skill the short and medium range skill of the operaTonal GEFS.
• The EGEFS was run for three periods during 2011-‐2012, corresponding to regular, strong and weak MJO.
• Raw forecasts show that skill averaged (in the NH) for each period correspond to the amplitude of MJO forcing
• It is an predicTon system of “opportunity” that will take advantage of the experiences and data from the CFSv2 and the ESRL’s hindcast.
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