# Presentation: 317517

## Recent Upgrade and Plans For NCEP Global Ensemble

- Yuejian Zhu,
-  David Michaud, Zoltan Toth, Richard Wobus and Mozheng Wei
- Environmental Modeling Center
- NOAA/NWS/NCEP
- Acknowledgements:
- Dingchen Hou, Ken Campana, Mark Iredell and Stephen Lord  EMC
- Brent Gordon and Luke Lin  NCO

## Analysis of Product Volume

- IBM CCS Disk
- NCEP Global Ensemble Forecast System (GEFS) Component of NAEFS
- Increase of 50 Gig/Cycle
- Increase of 659 Gig Total Disk Storage (18 Days for Bias Correction)
- CMC Component of NAEFS
- Increase of 3.5 Gig/Cycle
- Decrease of 27 Gig Total Disk Storage (18 Days for Bias Correction)
- Total Increase of 633 Gig Total Disk Storage for NAEFS
- IBM CCS Tape Storage
- Increase of 23 Gig/Day
- FTPPRD
- Increase of 8 Gig/Day
- NWS TOC FTP Server
- Increase of 1 Gig/Day

## Analysis of Production Resources

## Analysis of Production Resources

|  | Production |  | Proposed |  |
| --- | --- | --- | --- | --- |
| Job Type | Members -Nodes/Tasks | Average Runtime (Min) | Members -Nodes/Tasks | Average Runtime (Min) |
| Initialization | 1/5 | 2.5 | 1/1 | 56 |
| Global Forecast
(0-384 Hours) | 11 – 3/24 | 32 | 15 – 2/16 | 36 |
| Global Post
(0-384 Hours) | 11 – 1/4 | 34 | 15 – 1/4 | 37 |

- NCEP GEFS Forecast (0-384 Hours)

- New System Fits Within Allocated Production Window

- End-to-End Runtime   38.5 Nodes	    37min	         37.5 Nodes	         37min

## Analysis of Production Resources

|  | Production |  | Proposed |  |
| --- | --- | --- | --- | --- |
| Job Type | Members -Nodes/Tasks | Average Runtime (Min) | Members -Nodes/Tasks | Average Runtime (Min) |
| Mean/Spread Post | 1/1 | 21 | 1/1 | 40 |
| Bias Correction
Climate Anom
Weights |  |  | 
1/8 | 
40 |
| GEMPAK | 2/11 | 0.5 | 1/8 | 40 |

- NCEP GEFS Post-Processing

- Post Processing for Proposed Implementation Run in Parallel with Forecast While Production Runs After Forecast
- Mean/Spread Post Starts Delivering Product 58 Minutes Earlier

## Planned Changes for GEFS- Summary

- 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
- Changes of File Names and Structures

## GEFS configurations

|  | Current | New |
| --- | --- | --- |
| Model | GFS | GFS |
| Initial uncertainty | BV | ETBV |
| Model uncertainty | None | None |
| Tropical storm | Relocation | same |
| Daily frequency | 00,06,12 and 18UTC | same |
| Hi-re control 
(GFS) | T382L64 (d0-d7.5)
T190L64 (d7.5-d16) | same |
| Low-re control (ensemble control) | T126L28 (d0-d16)
00UTC only | T126L28 (d0-d16)
00,06,12 and 18UTC |
| Perturbed members | 10 for each cycle | 14 (20) for each cycle |
| Forecast length | 16 days (384 hours) | same |
| Implementation  | August 17th 2005 | May 30th 2006 |

_**GEFS configurations**_

## Ensemble Transform Bred Vector

- P1

- N1

- P2

- N2

- P#, N# are the pairs of positive and negative
- P1 and P2 are independent vectors
- Simple scaling down (no direction change)

- _Ensemble Transform Bred Vector_
- (New)

- 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.

- _Rescaling_

**ANL**

**ANL**

**ANL**

- _Bred Vector_
- (Current)

_**P1 forecast**_

_**P4 forecast**_

_**P3 forecast**_

_**P2 forecast**_

- t=t1

- t=t0

- t=t0

- t=t2

- t=t2

- t=t1

- _Rescaling_

## Changes of File Names and Structures

- Pressure GRIB Files Split into Two
- Pgrba – 51 Variables For NAEFS Exchange
- Pgrbb – Remaining 278 Variables
- Perturbation runs from pairs to single size
- P1, n1, p2, n2 ... convert to p0, p02, p03, p04 ...
- Enspost.* and Ensemble.* Files Eliminated
- Data Was Duplicate to Pressure GRIB Data Packed in Different Format
- Ensemble Extensions Corrected in Pressure GRIB Files
- 6-Hourly Precipitation/Max/Min Accumulations Available in Pressure GRIB Files
- GEMPAK Files Created for NAEFS Members for Raw and Bias Corrected pgrba Files
- GEMPAK Metafiles For HPC Medium Range Desk Created in Production

## Early studies for ET

- Northern Hemisphere

- Southern Hemisphere

- Tropical

_**Early studies for ET**_
- Winter of 2002-2003
- ROC scores for 32 cases
- ENS-o  control runs
- ENS-s  ET-20 members
- ENS-x  ET-10 members

## 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)

## GFS TS relocation

- Fcst/guess

- 3hrs

- 9hrs

- 6hrs

-       Relocated TS to
-      Observed position

**GDAS**
**(SANL)**

**FCST**

- P

- C

- N

- _6hrs fcst_

**Use ens. Track information**

**Use GFS Track information**

**Use GFS Track information**

**Use ens. Track**
**information**

- To separate into env. Flow (EF)
- And storm perturbation (SP)

**FCST**

- Ensemble TS relocation

- Ens. Rescaling
- For SP (p+n)

- Ens. Rescaling
- For EF (p+n)

- Combined

- _August 2005 Implementation_

## Track errors and spreads2004 Atlantic Basin (8/23-10/1)

- From Timothy Marchok (GFDL)

- Reduced mean track errors and spreads

## Hurricane track errors2 basins (Atlantic and e-Pacific)

- Track errors (miles)

- Percentage improvement to operational ensemble

- Period: 20040824-20040930 (53-103 cases)

## Hurricane Track Errors (Period: 08/20-09/30/2005)

**Cases      174      157      141      128      101       75         48**

**Hours**

- _ENSs-operational ensemble_
- _ENSx-retrospective runs_
- _GFSs-operational GFS_

_**Atlantic Basin**_

**Cases      181      165     149      135      109       85         69**

**Cases      177      161      145      129      101       66         44**

**Cases      532      483      435      392      311       226      161**

_**All Basins**_

_**West Pacific Basin**_

_**East Pacific Basin**_

## Ensemble mean evaluations

- _Improving skills from/after day 3_

- _Much better than GFS after 72 hours_

- _65% AC scores – useful skill_
- _Ens. extended add. 20 hours_

- _ENS_s – opr. ensemble_
- _ENS_x – retrospective runs_

- _Improved_

- _RMSs are very similar_

- _RMSs are very similar_

- _ENS_s – opr. ensemble_
- _ENS_x – real time parallel_

- Northern Hemisphere

- Southern Hemisphere

- Right – Real Time Parallel

- Left – Retrospective Runs

## Probabilistic Evaluation (ROC)

- _ENS_s – operational ensemble_
- _ENS_x – retrospective runs_

- _ENS_s – operational ensemble_
- _ENS_x – real time parallel runs_

- _Improved_

- _Improved_

- _Improved_

- _Improved_

- Northern Hemisphere

- Right: Real Time Parallel

- Left: Retrospective Runs

- Southern Hemisphere

## Probabilistic Evaluation (RPSS)

- _ENS_s – operational ensemble_
- _ENS_x – retrospective runs_

- _ENS_s – operational ensemble_
- _ENS_x – real time parallel runs_

- _Improved_

- _Improved_

- _Improved_

- _Improved_

- Northern Hemisphere

- Right: Real Time Parallel

- Left: Retrospective Runs

- Southern Hemisphere

## Tropical scores for

- _There is no big effect in Tropical by apply ET in generally_

- _Probabilistic skills_

_**Tropical scores for**_
_**NCO real time parallel**_

_**Ensemble mean**_

_**Ensemble probabilistic**_

## Perturbation versus Error Correlation Analysis (PECA)

- Retrospective runs

- NCO parallel runs

## NCEP GEFS Plans

- New computer will be in operation by early 2007
- Increasing the power of factor of 3-5
- GEFS Configurations
- 20 members each cycle by early 2007
- Increasing horizontal/vertical resolution by later 2007
- Either T126/L64 (keep same horizontal resolution)
- Or T170/L42
- Stochastic perturbation Scheme
- Representing model related uncertainty
- Assumption: the perturbations (diff. Between ens. Numbers and ctl) in the conventional tendencies provide a sample of realizations of additional stochastic forcing “S”
- Strategy: Generate the “S” term from (random) liner combination of the conventional perturbation tendencies.
- General approach: adding a stochastic forcing term “S” into the tendencies of the model equations.
- Desired properties: forcing applied to all variables; approximately balanced; smooth variation in space and time; flow dependent and quasi-orthogonal.
- Expected results: increased spread, reduced systematic error and improved probabilistic forecast

## NAEFS Configuration Review (NCEP)

** **

## Background !!!!!

## NAEFS Performance Review

**KEY PERFORMANCE MEASURES**

** **
_** **_

## Representing Model Related UncertaintyA Proposed Stochastic Perturbation Scheme

**Strategy**: Generate the S terms from (random) linear combinations of the conventional perturbation tendencies.

**General Approach: **Adding a stochastic forcing term in to the tendencies of the model equations.
**Assumption: **The perturbations (difference between ensemble members and the control) in the conventional tendencies provide a sample of realizations of the additional stochastic forcing S.

**Desired Properties **
- 1.    Forcing applied to all variables
- 2.   Approximately balanced
- 3.   Smooth variation in space and time
- 4.    Flow dependent
- 5.    Quasi-orthogonal

**Expected Results**
- Increased spread
- Reduced systematic error
- Improved probabilistic forecast

## Outliers: H500, day 6 forecast, 20041002 

**Without SP**
- large number of outliers with
- negative and positive forecast bias

**With SP**
- the number of outliers is
- significantly reduced

## Statistics: Ensemble Spread and Error of Ensemble MeanIncreased Spread, Reduced Mean Error (ME)Reduced Mean Absolute Systematic Error (MASE)----- Without SP      ------- With SP

- MASE

- Mean Error

- Mean Error

- Solid, rmse
- Dash: spread

- Solid: rmse
- Dash: spread

## Comparison with Post-Processing (PP) RPSS: Improved in both cases (SP and PP)SP is more effective in week 2 forecast

- ---- Without SP
- ---- With SP
- ---- Without SP
-     but optimal pp
-     (upper limit)

- ---- Operation
- ---- Operation +1%PP
- ---- Operation +
-        optimal pp
-        (upper limit)

- Stochastic Parameterization (SP)

- Bias-correction (1%PP)