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Applications of Ensemble Prediction - a Historical Perspective Steve Tracton Office of Naval Research Arlington, VA (Formally of NWS/NCEP) KEY POINTS THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION SCREAMING MESSAGE:

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Applications of ensemble prediction a historical perspective l.jpg

Applications of Ensemble Prediction - a Historical Perspective

Steve Tracton

Office of Naval Research

Arlington, VA

(Formally of NWS/NCEP)


Key points l.jpg
KEY POINTS Perspective

THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION

SCREAMING MESSAGE:

THERE WILL ALWAYSBE VARYING DEGREES OF UNCERTAINTIES IN FORECASTS (“Chaos Theory”)


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KEY POINTS Perspective

THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION

ENSEMBLE PREDICTION – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”),

First formal attention to the real possibility of OPERATIONAL

ensemble prediction at ECMWF Workshop on Predictability

In the Medium Range and Extended Range, 1986

Ultimately led to operational GLOBAL EPS at ECMWF and

NMC in Dec 1992

Followed from

Sufficient CPU resources becoming available

Scientific basis for generating “dynamically

constrained” initial state perturbations (SVs, Breeding)

Development of output products


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Give Me Odds Perspective

ENSEMBLE FORECASTING


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KEY POINTS Perspective

THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION

ENSEMBLE PREDICTION – FROM EARLY 90’S ON, REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”), THE OBJECTIVES BEING TO:

PROVIDE RELIABLE INFORMATION ON FORECAST UNCERTAINTIES FROM THE SPREAD (DIVERSITY) AMONGST ENSEMBLE MEMBERS

USE TO:

  • Ascertain most likely deterministic prediction

  • Confidence in deterministic forecast

  • Same, plus identifying relative likelihood of alternative scenarios

  • Full probability distribution – maximum information

  • NET RESULT - ENHANCE UTILITY/VALUE OF NWP FOR VIRTUALLY ALL APPLICATIONS

NOT NECESSARILY SKILL


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Providing EPS = Acceptance and Use Perspective

/

MRF

ECMWF

NOGAPS

UKMET


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WHICH SOLUTION IS PREFERRED? Perspective

 DETERMINISTIC THINKING

RUN TO RUN MODEL CONTINUITY

TODAY’S DAY 3

YESTERDAY’S DAY 4

GOOD

NEW 84

HR MRF

OLD 108

HR MRF

BAD

NEW 96 HR

ECMWF

OLD 120

HR ECMWF


Hpc s extended forecast discussion released mar 2 2001 at 3 38 p m l.jpg

EPS NOW CONSIDERED INDISPENSIBLE TO HPC MEDIUM RANGE FORECASTS (Jim Hoke)

HPC’s Extended Forecast Discussion(released Mar 2, 2001, at 3:38 p.m.)

STEEP LEARNING CURVE

FOR NEW PARADIGM:NO A- PRIORI BEST SINGLE OUTCOME

“DETERMINISM IS DEAD” ??

NOT YET; BUT…


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American Meteorological Society (AMS) Statement: Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

“The AMS endorses probability forecasts and recommends their use be substantially increased.”

“Would allow user (not forecaster!) to make decisions based on quantified uncertainties with resulting economic and social benefits” ( e.g., from taking umbrella along, through canceling a trip ,to evacuation from an impending threat)


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Schematic of how a probabilistic model forecast can be used for risk-based decision-making.

P1

P2

P3

P4

.

.

PN

F(P)

Model

Pcr

Compare T

with Tcr

Take

appropriate

action

T

P

P1, P2 … PN = predicted variables of interest, for example, precipitation amount

Pcr = user-specified “critical value” of P which, if exceeded, requires an action or decision

T = chance of critical value being exceeded

Tcr = user-specified tolerance level (depending on societal, monetary, and/or environmental considerations).


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American Meteorological Society (AMS) Statement: Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

“The AMS endorses probability forecasts and recommends their use be substantially increased.”

“Would allow user (not forecaster!) to make decisions based on quantified uncertainties with resulting economic and social benefits” ( e.g., from taking umbrella along, through canceling a trip, to evacuation from an impending threat)

“Probability Forecasts are particularly useful, even necessary, to reliably provide early warnings of extreme weather events”

TO AVOID, E.G.


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MAJOR SNOWSTORM AMBUSHES WASHINGTON Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

Not Good- especially when effecting DC (just after announce-ment of new Super Computer by NWSHQ


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FOR FORECASTERS, ANOTHER … Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)


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American Meteorological Society (AMS) Statement: Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

“The AMS endorses probability forecasts and recommends their use be substantially increased.”

“Would allow user (not forecaster!) to make decisions based on quantified uncertainties with resulting economic and social benefits” ( e.g., from taking umbrella along through canceling a trip to evacuation from an impending threat)

Requires:

Conveying rationale and nature of uncertainties

Products/graphics/presentations that are readily comprehensible and relevant


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KEY POINTS Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

THERE ARE INEVITABLE UNCERTAINTIES IN NWP DUE TO UNCERTAINTIES IN INITIAL CONDITIONS AND MODEL FORMULATION

ENSEMBLE PREDICTION - REVOLUTIONARY CHANGE IN THE THRUST OF OPERATIONAL NWP (“WAVE OF THE FUTURE”) - CONSISTS OF MULTIPLE PREDICTIONS FROM SLIGHTLY DIFFERENT INITIAL CONDITIONS AND/OR WITH VARIOUS VERSIONS OF MODELS, THE OBJECTIVES BEING TO:

REALIZING THE PRACTICAL UTILITY/VALUE OF ENSEMBLES ACCOMPLISHED VIA A VARIETY OF PRODUCTS DESIGNED TO CONDENSE AND MAXIMIZE INFORMATION CONTENT FOR USERS

Products/graphics/presentations must be readily comprehensible

and relevant

(MUST BE USER SPECIFIC AND USER FRIENDLY)

USER FEEDBACK ESSENTIAL


Products stamp maps l.jpg
Products: Stamp maps Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)


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TYPES OF PRODUCTS Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

Roots of EPS products largely provided by Ed Epstein with graphical depictions to illustrate how uncertainty information could enhance forecast value (1971);

But, no further formalconsideration of post processing and presenting EPS output until 1992 ECMWF Workshop on New Developments in Predictability (List of recommended generic products largely reflected “concept demonstration” mode of EPS experiments at NMC/CAC, Tracton and Kalnay, 1993)

 SPAGHETTI CHARTS: now one of the most recognizable and symbolic products of EPS


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TYPES OF PRODUCTS Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

SPAGHETTI CHARTS

MEAN/SPREAD

PROBABILITIES

STORM TRACKS

CLUSTERS

VERTICAL PROFILES

METEOGRAMS

ENSEMBLE DERIVED MOS


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010519/0000V63 SREFX-CMB; LIFTED INDEX PROB 0F < -4 Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)


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5-Day ECMWF Ensemble Prediction of Typhoon Rusa Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)


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TYPES OF PRODUCTS Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

SPAGHETTI CHARTS

MEAN/SPREAD

PROBABILITIES

STORM TRACKS

CLUSTERS

VERTICAL PROFILES

METEOGRAMS

ENSEMBLE DERIVED MOS

  • CAN BE APPLIED TO VIRTUALLY ALL MODEL AND MODEL DERIVED PARAMETERS AND MODEL OUTPUT DRIVERS OF SECONDARY SYSTEMS, E.G., WAVE, HYDROLOGICAL,POLUTION DISPERSION MODELS

ULTIMATELY CAN (MUST) BE PROPOGATED TO USER SPECIFCIC

QUANTITIES, E.G., UMBRELLA SALES, ENERGY USEAGE, TYPE

OF “SMART” MUNITIONS, ETC., ETC., ETC., ETC., ETC., ETC ….


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MANY NEW AND VARIED PRODUCTS POSSIBLE; Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

BUT, MOST SIGNIFICANT ADVANCE OVER PAST YEARS HAS BEEN EXPONENTIAL GROWTH IN GRAPHICS CAPABILITIES - ANIMATION, ZOOMING, 3-D, ETC. - AND PROLIFERATION OF PCs AND HIGH SPEED INTERNET


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MANY NEW AND VARIED PRODUCTS POSSIBLE; Enhancing Weather Information with Probability Forecasts (3/02 BAMS!)

BUT, MOST SIGNIFICANT ADVANCE OVER PAST YEARS HAS BEEN EXPONENTIAL GROWTH IN GRAPHICS CAPABILITIES - ANIMATION, ZOOMING, 3-D, ETC. - AND PROLIFERATION OF PCs AND HIGH SPEED INTERNET

SO, REAL CHALLENGE IS MORE FULLY EXPLOITING POTENTIAL VALUE OF EPS IN BOTH PUBLIC AND PRIVATE SECTORS



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MON TUES WED THURS FRI

40%

36 28 23 21 31

40

30

20

THIS

10



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Visualizing Uncertainty FRI inMesoscale Meteorology

APL Verification Methodology

21 May 2002

Scott Sandgathe





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END FRI




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  • High Resolution Mesoscale models FRI

    • allow us to see features not in coarser models

    • But: even small timing and placement errors can be significant in attempt to accurately forecast details (see Mass, et al., 3/02 BAMS!!!).

    • ButBut: Forcaster judgement could mitigate

  • One model (even with forecaster input)

  • is an all or nothing proposition =>

“One detailed mesoscale model based

forecast could allow the user to

make highly specific and detailed

inaccurate forecasts.” (after Grumm)


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  • Why we need ensembles FRI

    • Deal with uncertainties in analyses and model formulation

    • But: Requires tradeoffs when computer resources limited (e.g., model resolution)

    • ButBut: Mesoscale predictability often substantially controlled by synoptic predictability (and uncertainties therein)

    • => Subjective or statistically based downscaling possible to get uncertainties in mesoscale weather

    • Ideal: Ensembles with highest resolution justifiable

    • Compromise: Combination of single (or few) high resolution and coarser resolved ensemble


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ADDITIONAL WEB SITES WITH ENSEMBLE PRODUCTS AND INFORMATION FRI

Univ of Utah:

http://www.met.utah.edu/jhorel/html/models/

model_ens.html

FNMOC:

http://152.80.49.204/PUBLIC/

Canada:

http://www.cmc.ec.gc.ca/rpn/ensemble_products/

index.html

CDC:

http://www.cdc.noaa.gov/~map/maproom/ENS/

ens.html

State College:

http://bookend.met.psu.edu/ensembles/Ensemble.html


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Give Me Odds FRI

ENSEMBLE FORECASTING



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YOUR FORECAST HAS A 30% FRI

CHANCE OF BEING 70% CORRECT


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3-day forecast from 00 UTC 11/2/01, spaghetti diagram for ensemble

global

Uncertain location of

incoming western trough

Uncertain amplitude

of eastern trough

From CDC web site:

http://www.cdc.noaa.gov/map/images/ens/ens.html


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ensembleSPAGHETTI” DIAGRAM

564 DM CONTOUR

NCEP ENSEMBLE

SOME NCEP ENSEMBLE MEMBERS OFFER A MORE “DIGGY” CENTRAL U.S. TROF THAN THE OPERATIONAL MRF..BUT NOT AS STRONG AS THE ECMWF

DAY3


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