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THE WINTER STORM RECONNESSAINCE PROGRAM OF THEUS NATIONAL WEATHER SERVICE

Zoltan Toth

GSD/ESRL/OAR/NOAAFormerly at EMC/NCEP/NWS/NOAA

Acknowledgements:

Yucheng Song – Plurality at EMCSharan Majumdar – U. Miami

Istvan Szunyogh – Texas AMUCraig Bishop - NRLRolf Langland - NRL

THORPEX Symposium, Sept 14-18 2009, Monterey, CA

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OUTLINE / SUMMARY

• History– Outgrowth of FASTEX & NORPEX research– Operationally implemented at NWS in 2001

• Contributions / documentation– Community effort– Refereed and other publications, rich info on web

• Highlights– Operational procedures for case selection, ETKF sensitivity calculations– Positive results consistent from year to year

• Open questions– Does operational targeting have economic benefits?– Can similar or better results be achieved with cheaper obs. systems?– What are the limitations of current techniques?

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HISTORY OF WSR

• Sensitivity calculation method– Ensemble Transform (ET) method developed around 1996

• Field tests– FASTEX – 1997, Atlantic

• Impact from sensitive areas compared with that from non-sensitive areas (“null” cases)

– NORPEX – 1998, Pacific• Comparison with adjoint methods

– CALJET, PACJET, WC-TOST, ATReC, AMMA, T-PARC

• WSR– 1999 - First test in research environment– 2000 - Pre-implementation test– 2001 - Full operational implementation

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CONTRIBUTIONS• Craig Bishop (NASA, PSU, NRL)

– ET & ETKF method development

• Sharan Majumdar (PSU, U. Miami)– ETKF method development and implementation

• Rolf Langland (NRL), Kerry Emanuel (MIT)– Field testing and comparisons in FASTEX, NORPEX, TPARC

• Istvan Szunyogh (UCAR Scientist at NCEP, U. MD, Texas AMU)– Operational implementation, impact analysis, dynamics of data impact

• Yucheng Song (Plurality at EMC/NCEP/NWS/NOAA)– Updates, maintenance, coordination

• Observations– NOAA Aircraft Operations Center (G-lV)– US Air Force Reserve (C130s)

• Operations– Case selection by NWS forecasters (NCEP/HPC, Regions)– Decision making by Senior Duty Meteorologists (SDM)

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DOCUMENTATION• Papers (refereed / not reviewed)

– Methods• ET Bishop & Toth• ETKF Bishop et al, Majumdar et al

– Field tests• Langland et al FASTEX• Langland et al NORPEX• Szunyogh et al FASTEX• Szunyogh et al NORPEX• Song et al TPARC (under preparation)

– Operational implementation• Toth et al 2 papers

– WSR results• Szunyogh et al• Toth et al (under preparation)

• Web– Details on procedures– Detailed documentation for each case in WSR99-09 (11 years, ~200+ cases)

• Identification of threatening high impact forecast events• Sensitivity calculation results• Flight request• Data impact analysis

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OPERATIONAL PROCEDURES • Case selection

– Forecaster input – time and location of high impact event• Based on perceived threat and forecast uncertainty

– SDM compiles daily prioritized list of cases for which targeted data may be collected

• Ensemble-based sensitivity calculations– Forward assessment

• Predict impact of targeted data from predesigned flight tracks– Backward sensitivity

• Statistical analysis of forward results for selected verification cases

• Decision process– SDM evaluates sensitivity results

• Consider predicted impact, priority of cases, available resources– Predesigned flight track # or no flight decision for next day– Outlook for flight / no flight for day after next

• Observations– Drop-sondes from manned aircraft flying over predesigned tracks

• Aircraft based in Alaska (Anchorage) and/or Hawaii (Honolulu)– Real time QC & transmission to NWP centers via GTS

• NWP– Assimilate all adaptively taken data along with regular data– Operational forecasts benefit from targeted data

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HIGHLIGHTS• Case selection

– No systematic evaluation available– Some errors in position / timing of threatening events in 4-6 day forecast range

• Affects stringent verification results– Need for objective case selection guidance based on ensembles

• Sensitivity calculations– Predicted and observed impact from targeted data compared in statistical sense– Sensitivity related to dynamics of flow

• Variations on daily and longer time scales (regime dependency)

• Decision process– Subjective due to limitations in sensitivity methods

• Spurious correlations due to small sample size

• Observations– Aircraft dedicated to operational observing program used– Are there lower cost alternatives?

• Thorough processing of satellite data• UAVs?

• NWP forecast improvement– Compare data assimilation / forecast results with / without use of targeted data

• Cycled comparison for cumulative impact• One at a time comparison for better tracking of impact dynamics in individual cases

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Pre

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Obs

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Figure 1. Winter Pacific forecasts: Verification of mean 500 hPa geopotential rmse up to day 10 for SEAOUT in grey dotted and SEAIN in black: Both experiments are verified using ECMWF operational analysis. Verification regions: (a) North Pacific, (b) North America, (c) North Atlantic and (d) the European region.

WHY TARGETING MAY WORKImpact of data removal over Pacific - Kelly et al. 2007

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FORECAST EVALUATION RESULTS

Based on 10 years of experience (1999-2008)

• Error reduced in ~70% of targeted forecasts– Verified against observations at preselected time / region

• Wind & temperature profiles, surface pressure

• 10-20% rms error reduction in preselected regions– Verified against analysis fields

• 12-hour gain in predictability– 48-hr forecast with targeted data as skillful as 36-hr forecast

without

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WSR Summary statistics for 2004-07

Variable# cases

improved# cases neutral

#cases degraded

Surface pressure 21+20+13+25=79 0+1+0+0=1 14+9+14+12=49

Temperature 24+22+17+24=87 1+1+0+0=2 10+7+10+13=40

Vector Wind 23+19+21+27=90 1+0+0+0=1 11+11+6+10=38

Humidity 22+19+13+24=78 0+0+0+0=0 13+11+14+13=51

25+22+19+26 = 92 POSITIVE CASES

0+1+0 +0 = 1 NEUTRAL CASE

10+7+8 +11 = 36 NEGATIVE CASES 71.3% improved 27.9% degraded

Wind vector error, 2007

With

out

targ

ete

d d

ata

With targeted data

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Valentine’s day Storm2007

• Weather event with

a large societal impact• Each GFS run

verified against its own analysis – 60 hr

forecast• Impact on surface pressure verification

• RMS error improvement: 19.7% (2.48mb vs. 2.97mb)

Targeted in high impact weather area marked by the circle

Surface pressure from analysis

(hPa; solid contours)Forecast Improvement (hPa;

shown in red)Forecast Degradation (hPa;

blue)

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Average surface pressure forecast error reduction from WSR 2000

The average surface pressure forecast error reduction for Alaska (55°–70°N, 165°–140°W), the west coast (25°–50°N, 125°–100°W), the east coast (100°–75°W), and the lower 48 states of the United States (125°–75°W). Positive values show forecast improvement, while negative values show forecast degradation

(From Szunyogh et al 2002)

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Forecast Verification for Wind (2007)

RMS error reduction vs. forecast lead time

10-20% rms error reduction in winds

Close to 12-hour gain in predictability

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Forecast Verification for Temperature (2007)

RMS error reduction vs. forecast lead time

10-20 % rms error reduction

Close to 12-hour gain in predictability

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CONCLUSIONS

• High impact cases can be identified in advance using ensemble methods

• Data impact can be predicted in statistical sense using ET / ETKF methods– Optimal observing locations / times for high impact

cases can be identified

• It is possible to operationally conduct a targeted observational program

• Open questions remain

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OPEN QUESTIONS• Does operational targeting have economic benefits?

– Cost-benefit analysis needs to be done for different regions – SERA research• Are there differences between Pacific (NA) & Atlantic (Europe)?

• Can similar or better results be achieved with cheaper observing systems?– Observing systems of opportunity

• Targeted processing of satellite data• AMDAR

– UAVs?

• Sensitivity to data assimilation techniques– Advanced DA methods extracts more info from any data

• Better analysis without targeted data• Larger impact from targeted data (relative to improved analysis with standard data)?

• What are the limitations of current techniques?– What can be said beyond linear regime?

• Need larger ensemble for that?– Can we quantify expected forecast improvement (not only impact)?

• Distinction between predicting impact vs. predicting positive impact– Effect of sub-grid scales ignored so far

• Ensemble displays more orderly dynamics than reality?– Overly confident signal propagation predictions?

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DISCUSSION POINTSHow to explain large apparent differences between various

studies regarding effectiveness of targeted observations?

• Case selection important– Only every ~3rd day there is a “good” case– Targeting is not cure for all diseases

• If all cases averaged, signal washed out at factor of 1/3

• Measure impact over target area– Effect expected in specific area

• If measured over much larger area, signal washes out by factor of 1/3• 2 factors above may explain 10-fold difference in quantitative assessment of utility in

targeting observations

• Not all cases expected to yield positive results– Artifact of statistical nature of DA methods

• Should expect some negative impact– Current DA methods lead to forecast improvements in 70-75% of cases

• Geographical differences– Potentially larger impact over larger Pacific vs smaller Atlantic basins?

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BACKGROUND

Example: Impact of WSRP targeted dropsondes

1 Jan – 28 Feb 2006 00UTC Analysis

NOAA-WSRP 191 Profiles

Beneficial (-0.01 to -0.1 J kg-1)

Non-beneficial (0.01 to 0.1 J kg-1)Small impact (-0.01 to 0.01 J kg-1)

Binned Impact

Average dropsonde ob impact is beneficial and ~2-3x greater than average radiosonde impact

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Composite summary maps

139.6W 59.8N 36hrs (7 cases) - 1422km 92W 38.6N 60hrs (5 cases)- 4064km

122W 37.5N 49.5hrs (8 cases) - 2034km 80W 38.6N 63.5hrs (8 cases) - 5143km

Verification Region

Verification Region

22 -8

-7

-6

-5

-4

-3

-2

-1

0 Satwind

AMSU-A

SSMI/PRH

Raob

Dropsonde

Aircraft

Land Sfc

Scatwind

Windsat

Modis

Ship Sfc

SSMI/Wnd

North Pacific observation impact sum - NAVDAS

1-31 Jan 2007 (00UTC analyses)Change in 24h moist total energy error norm (J kg-1)

Error Reduction

23 -10-9

-8-7

-6-5

-4-3

-2-1

0 Satwind

AMSU-A

SSMI/PRH

Raob

Dropsonde

Aircraft

Land Sfc

Scatwind

Windsat

Modis

Ship Sfc

SSMI/Wnd

Error Reduction

(x 1.0e5)

Change in 24h moist total energy error norm (J kg-1)

1-31 Jan 2007 (00UTC analyses)

North Pacific forecast error reduction per-observation

Ship Obs

Targeted dropsondes =

high-impact per- ob, low total

impact

24

3649.5

60

63.5

0

1000

2000

3000

4000

5000

6000

0 20 40 60 80

Forecast Hours

Dis

tan

ce (

km)

ETKF predicted signal propagation

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Precipitation verification

• Precipitation verification is still in a testing stage due to the lack of station observation data in some regions.

20.4416.50OPR

18.5616.35CTL

3:14:1Positive vs. negative

cases

10mm 5mm ETS