Experimental Extended Range GEFS

Transcription

1 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

2 Global operatonal ensemble predicton systems at NCEP Both use the GFS as the Atmospheric component CFSv2 GEFS Coupled Yes Atmos- Land Ensemble size ResoluTon T126L64 T254L42 Year of operaton Ensemble GeneraTon Lagged ETR Community served Climate Weather Hindcast CFSRR (Saha et al) ESRL (Hamill et al) CFS - > NMME, IMME GEFS - > NAEFS, TIGGE 2

3 Historical RPSS for GEFS 20 Member Ensemble every 6h Befer than predictng climatology GEFS constantly improving: I.C., higher resoluton, GFS, perturbaton methods GEFS currently outperforms climatology beyond 16 days; slowly approaching to zero 3

4 ConTnuos Rank Probability Score 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 = 1 Cases Cases i=1 "F # fcst i (x) F obs i (x) $ % dx 2 CRPSS = (C CRPS) / C 4

5 10- day lead skill and the MJO AC score From Yuejian Zhu CRPSS From Yuejian Zhu WH Time Series of Mag(RMM1, RMM2) WH Time Series of Mag(RMM1, RMM2)

6 Lingering predicton skill beyond 2 weeks? or Beginner s Luck? AC of RMM1 and RMM2 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? Courtesy of Qin Zhang (CPC) 6

7 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

8 Three experimental periods Regular Strong Weak 8

9 CFSv2 hindcast skill Courtesy of Qin Zhang (CPC) 9

10 WH- MJO Forecast Skill GEFS Ensemble Mean Raw Regular Case Courtesy of Qin Zhang (CPC) 10

11 WH- MJO Forecast AC Skill GEFS Ensemble Mean Raw Strong Case Courtesy of Qin Zhang (CPC) Compare AC at lead 0 11

12 WH- MJO Forecast Skill GEFS Ensemble Mean Raw Weak Case Courtesy of Qin Zhang (CPC) We don t expect the EGEFS as it is now to be a good predicton model when MJO is weak 12

13 CRPSS Strong ~ 19 days Weak ~ 16 days 13

14 RMSE and Spread Weak Strong Spread Spread Default stochastc parameters 14

15 Forecast uncertainty in the tropics Area of current development Weak Weak 15

16 New approach to estmate uncertainty Peña and Toth 2014 under review in Tellus 16

17 Lagged forecasts OperaTonal GEFS Experimental GEFS Forecast Lead (days) Forecast Lead (days) 17

18 Lagged 16 mem vs 20 mem at 00Z

19 Gridpoint- wise SystemaTc Error of the 500hPa (m)

20 Gridpoint- wise SystemaTc Error of the 500hPa

21 Gridpoint- wise SystemaTc Error of the 500hPa

22 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 Nov

23 Several deficiencies reported Hamill and Kiladis 2013 Under- dispersive MJO (The reforecast has 6 members only) 23

24 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 24

25 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 25

26 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 , 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. 26