Recent Developments with the NCEP GEFS

1
Recent Developments with the NCEP GEFS

• Yuejian Zhu,
• Zoltan Toth, Richard Wobus, Qingfu Liu and
  Mozheng Wei
• Environmental Modeling Center
• NOAA/NWS/NCEP
• Acknowledgements
• Bo Cui, DingChen Hou, Mark Iredell and Stephen
  Lord EMC
• David Michaud, Brent Gordon and Luke Lin NCO

2
GEFS Changes (Aug. 2005)

• Extend T126 portion of forecast after 180 hours
• This change is intended to improve ensemble
  support for 5-10 days and week-2 forecast by
  providing high resolution (T126) and continue (no
  resolution change) forecast
• Results
• Increased spread for week-2 forecast
• Improving probabilistic skill beyond 180 hours
• Initial perturbations (breeding cycle), 6-hour
  instead of 24-hour cycle (see next slide)
• This change is intended to enable for relocation
  of perturbed tropical storm. Tuning initial
  perturbation size is for reducing spread for
  short-range forecast
• Results
• Decreased spread for short-rang (1-3) forecast
• Improving forecast skill for first 3 days
• Improving probabilistic forecast skill for short
  lead-time

3
Current breeding cycle 24 hours
New breeding cycle 6 hours
Re-scaling
24hrs
Up to 16-d
6hrs
Up to 16-d
Next T00Z
T00Z 10m
T00Z 40m
Re-scaling
24hrs
Up to 16-d
Re-scaling
T06Z 10m
T06Z 40m
Up to 16-d
Re-scaling
24hrs
Up to 16-d
Re-scaling
T12Z 10m
T12Z 40m
Re-scaling
Up to 16-d
24hrs
Up to 16-d
Re-scaling
T18Z 10m
T18Z 40m
Re-scaling
Up to 16-d
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GEFS Changes (Aug. 2005, Cont.)

• Relocation of Perturbed tropical storm
• Add 5 of TS to initial perturbation
• This change is intended to reduce track forecast
  error and uncertainty for short lead-time (1-3
  days)
• Results
• Reducing mean track errors by 10 for 12-48 hours
• Reducing the ensemble track spread (uncertainty)
  for short lead-time
• Improving track forecast skills

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GFS TS relocation
Ensemble TS relocation
6hrs fcst
Fcst/guess
3hrs
9hrs
6hrs
P
N
C
Use GFS Track information
Use ens. Track information
Use ens. Track information
Relocated TS to Observed position
Use GFS Track information
To separate into env. Flow (EF) And storm
perturbation (SP)
GDAS (SANL)
Ens. Rescaling For SP (pn)
Ens. Rescaling For EF (pn)
Combined
FCST
FCST
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Hurricane Track Plots (case 1)
Frances (08/28)
With relocation
Without relocation
Reduced initial spread
Large initial spread
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Hurricane Tracks Plots (case 2)
Ivan (09/14)
Without relocation
With relocation
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Track errors and spreads2004 Atlantic Basin
(8/23-10/1)
From Timothy Marchok (GFDL)
Reduced mean track errors and spreads
9
Hurricane track errors2 basins (Atlantic and
e-Pacific)
Percentage improvement to operational ensemble
Track errors (miles)
Period 20040824-20040930 (53-103 cases)
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GEFS Changes (May 2006)

• Increase the number of perturbed ensemble members
• 14 (in place of current 10) perturbed runs for
  each cycle (20 by early 2007)
• NAEFS requirement
• This change is intended to improve ensemble based
  prob. forecasts
• Results improved probabilistic skill, slightly
  improved ensemble mean skill (seasonally
  dependent)
• Add control runs for 06, 12 and 18Z cycles
• This change is intended to enable for relocation
  of perturbed tropical storm
• Facilitates comparison of high lower resolution
  ensemble controls
• If lores control and ensemble mean differ
  indication of nonlinearities
• If high lores controls differ indication for
  possible effect of resolution
• Introduce Ensemble Transform (ET) into GEFS
  breeding method
• ET breeding method creates globally orthogonal
  initial perturbations
• Uses simplex method to create individual (not
  paired) perturbations
• This change is intended to improve probabilistic
  forecast skill
• Results Improved probabilistic forecast skill
  Slightly reduced ensemble mean hurricane track
  errors for 12-96 hours

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GEFS configurations
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Ensemble Transform Bred Vector (New)
Bred Vector (Current)
Rescaling
Rescaling
P1 forecast
P2 forecast
P1
ANL
ANL
N1
P3 forecast
P4 forecast
tt1
tt0
tt2
tt0
tt2
tt1
P, N are the pairs of positive and negative P1
and P2 are independent vectors Simple scaling
down (no direction change)
P1, P2, P3, P4 are orthogonal vectors No pairs
any more To centralize all perturbed vectors (sum
of all vectors are equal to zero) Scaling down by
applying mask, The direction of vectors will be
tuned by ET.
P2
ANL
N2
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Summary of Retrospective and Parallel Runs

• Period
• 08/20/2005 09/30/2005 (retrospective runs)
• 03/01/2006 04/26/2006 (NCO real time parallel)
• Statistics for
• Hurricane track errors (retrospective runs only)
• Atlantic-, East Pacific-, West Pacific- basins,
  total basins
• RMS errors and AC scores for ensemble mean
• NH and SH ex-tropic
• Probabilistic verifications (ROC)
• NH and SH ex-tropic
• Conclusions
• Tropical mean of track error (slightly
  improved)
• Improved (48-, 72-, 96-hours over all)
• Northern hemisphere
• Mean -improved from retrospective runs-similar
  from NCO real time
• Probabilistic (improved)
• Southern hemisphere
• Mean similar from retrospective runs -improved
  from NCO real time
• Probabilistic (improved)

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Hurricane Track Errors (Period 08/20-09/30/2005)
Atlantic Basin
East Pacific Basin
ENSs-operational ensemble ENSx-retrospective
runs GFSs-operational GFS
Hours
Cases 174 157 141 128
101 75 48
Cases 181 165 149 135 109
85 69
All Basins
West Pacific Basin
Cases 177 161 145 129
101 66 44
Cases 532 483 435 392
311 226 161
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Ensemble mean evaluations
Improving skills from/after day 3
65 AC scores useful skill Ens. extended add.
20 hours
ENS_s opr. ensemble ENS_x real time parallel
Northern Hemisphere
RMSs are very similar
ENS_s opr. ensemble ENS_x retrospective runs
Much better than GFS after 72 hours
Right Real Time Parallel
Left Retrospective Runs
Southern Hemisphere
RMSs are very similar
Improved
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Probabilistic Evaluation (ROC)
ENS_s operational ensemble ENS_x
retrospective runs
Improved
Northern Hemisphere
Improved
ENS_s operational ensemble ENS_x real time
parallel runs
Right Real Time Parallel
Left Retrospective Runs
Improved
Southern Hemisphere
Improved
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First Implementation of NAEFS Summary

• Bias corrected members of joint MSC-NCEP ensemble
• Decaying accumulated bias (past 50 days) for
  each var. for each grid point
• For selected 35 of 50 NAEFS variables
• 32(00Z), 15(06Z), 32(12Z) and 15(18Z) joint
  ensemble members
• Bias correction against each centers own
  operational analysis
• Weights for each member for creating joint
  ensemble (equal weights now unequal weights to
  be added later)
• Weights dont depend on the variables
• Weights depend on geographical location (low
  precision packing)
• Weights depend on the lead time
• Climate anomaly percentiles for each member
• Based on NCEP/NCAR 40-year reanalysis
• Used first 4 Fourier modes for daily mean,
• Estimated climate pdf distribution (standard
  deviation) from daily mean
• For selected 19 of 50 NAEFS variables
• 32(00Z), 15(06Z), 32(12Z) and 15(18Z) joint
  ensemble members
• Adjustment made to account for difference between
  oper. re-analysis
• Provides basis for downscaling if local
  climatology available
• Non-dimensional unit

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Bias Correction Method Application

• Bias Assessment adaptive (Kalman Filter type)
  algorithm

decaying averaging mean error (1-w) prior
t.m.e w (f a)
For separated cycles, each lead time and
individual grid point, t.m.e time mean error
6.6

• Test different decaying weights.
• 0.25, 0.5, 1, 2, 5 and
• 10, respectively
• Decide to use 2 ( 50 days)
• decaying accumulation bias
• estimation

3.3
1.6
Toth, Z., and Y. Zhu, 2001

• Bias Correction application to NCEP
  operational ensemble 15 members

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List of Variables for Bias Correction,
Weightsand Forecast Anomalies for CMC NCEP
Ensemble
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Summary of NAEFS First Implementation

• Period
• 04/10/2006 Current (NCO real time parallel)
• Maps comparison for bias (before and after)
• 500hPa height, 2m temperature
• Statistics for
• Bias reduction in percentage
• Height, temperature, winds
• RMS errors
• Probabilistic verifications (ROC)
• NH, SH and tropic
• Conclusions
• Bias reduced (approximately 50 at early lead
  time)
• RMS errors improved by 9 for d0-d3
• Probabilistic forecast
• Improved for all area, all lead time
• Typically for NH, 20-24 hours improvement from d7

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500hPa height 120 hours forecast (ini
2006043000)
Shaded left raw bias
right bias after correction
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2 meter temperature 120 hours forecast (ini
2006043000)
Shaded left raw bias
right bias after correction
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Bias Improvement (absolute value) after Bias
correction
Overall bias reduction (globally) D0-3
50 D3-8 40 D8-15 30
500hPa height
850hPa temperature
There is daily variation after bias correction,
more bias reduced for valid 12Z cycle
Sea level pressure
2m Temperature
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Bias Improvement (absolute value) after Bias
correction
10m V-component
10m U-component
Overall bias reduction (Tropic) D0-3 50 D3-8
45 D8-15 40
Sea level pressure
2m temperature
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Evaluation after bias correction (16 cases)
Probabilistic skill Extended 20-h for d-7
Northern Hemisphere
Southern Hemisphere
Black-operational ensemble (10m) Red-real time
parallel ensemble (14m) Green-real time parallel
ensemble after bias correction (14m)
RMS errors for ensemble mean reduced for 48-h
forecast (9)
Tropics
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NAEFS Performance Review
Appendix 6 KEY PERFORMANCE MEASURES
   
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NAEFS Configuration Review (NCEP)
Appendix 8 MINIMAL (PREFERRED) CONFIGURATION FOR
THE GLOBAL ENSEMBLE FORECAST SYSTEMS OPERATIONAL
AT CMC AND NCEP  
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GEFS Major Implementation Plan (FY07)

• Upgrade vertical resolution from 28 to 64 levels
  for 20 perturbed forecasts
• 4 cycles per day
• T126L64
• Up to 384 hours (16 days)
• Real-time generation of hind-cast at T126/L64
  resolution.
• 4 cycles per day
• 27 hind-casts for each cycle since 1979
• Using reanalysis II initial conditions (T62L28
  resolution)
• Add random noise to high frequency (T63-T170) by
  using
• Cycling (6-hr T170 model forecast)
• Other method?
• (Alternate) upgrade both horizontal and
  vertical resolution to T170/L64
• Introduce ESMF scheme that allows concurrent
  generation of all ensemble members.
• Add stochastic perturbation scheme to account for
  model errors (tentative plan)

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NAEFS upgrade plan (FY07)

• Add approximately 15 new variables to current 51
  pgrba for NAEFS data exchange.
• Such as vertical shear, helicity, u,v, t, RH for
  100, 50hPa, LH, SWR, LWR at surface, and etc..
• Add GFS high resolution control bias correction
  by using current method for ensemble.
• There is a problem when we estimate bias after
  GFS change resolution after 180 hours
• Set up GFS low resolution (ensemble) control run
  on NCOs real time parallel prior to GFS upgrade
  in the future.
• As bias estimation of GFS major/minor
  implementation
• Need to compare the bias of ensemble mean and
  control
• Improve bias correction algorithm.
• Pending on hind-cast information
• Two weights one from real-time (analysis and
  forecast) bias estimation (mainly for week-1),
  another one from hind-cast (mainly for week-2)

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NAEFS Expansion and Future Plan

• Plans to be coordinated with THORPEX
• Links with Phase-2 TIGGE archive and beyond
  (GIFS)
• Expansion
• FNMOC
• Experimental data exchange by Dec 2006
• Preliminary evaluation by Dec 07
• Operational implementation by Dec 08 (subject to
  improved performance)
• UK Metoffice
• Decision on going operational possibly joining
  NAEFS - by 2008
• KMA, CMA, JMA
• Expressed interest, no detailed plans yet
• Data exchange with MSC
• Replace current ftp with more reliable telecom by
  Dec 08
• Statistical post-processing
• Continual enhancements to current methods (2nd
  moment correction, addtnl vars)
• Testing (Dec 08) possible implementation (09)
  of advanced methods
• Products
• Week-2 experimental by Nov 06
• Web graphics

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THORPEX LINKSPRODUCT DEVELOPMENT

• Goals
• Develop new numerical modeling applications
• Develop new product generation tools and products
• Participants / Contributions
• Scott Jacobs et al. (NCO)
• NAWIPS ensemble functionalities
• Richard Verret et al. (Meteorological Service of
  Canada, MSC)
• NAEFS web-based products
• David Unger et al. (CPC) and Richard Verret et
  al. (MSC)
• Week-2 NAEFS products
• Bob Grumbine (EMC)
• Sea ice ensemble application
• Dingchen Hou (EMC)
• River flow ensemble application
• Steve Silberberg, Binbin Zhou (NCEP)
• Aviation weather guidance
• Yuejian Zhu (NCEP)
• NAEFS coordination

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Background !!!!!
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RPSS before/after bias correction
RPSS performance for past 5 years