Extreme waves at the great lakes performance of ncep s operational wave models
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Extreme Waves at the Great Lakes: Performance of NCEP’s Operational Wave Models. Jose-Henrique Alves Research Scientist [email protected]/NCEP/EMC. Outline. General Views Past numerical wave models Present Op models Description of op systems at NCEP Performance in typical condtions

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Extreme Waves at the Great Lakes: Performance of NCEP’s Operational Wave Models

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Extreme Waves at the Great Lakes: Performance of NCEP’s Operational Wave Models

Jose-Henrique Alves

Research Scientist

[email protected]/NCEP/EMC


Outline

  • General Views

    • Past numerical wave models

    • Present Op models

  • Description of op systems at NCEP

  • Performance in typical condtions

  • Performance in severe storms

  • Improving model performance during storms

  • What future lies ahead?


General Views: Numerical Ancestry

  • 1974: First Automated NWS wave forecasts for Great Lakes

    • Pore (1979) based on Bretschneider (1970) fetch relations

    • Predictions at set of 64 point in five major lakes

    • Fetches radiating from points in 24 directions

  • Late 70’s: Two-dimensional grid using 2G wave model

    • Mark Donelan’s wave model from an unpublished 1977 report

    • Tweaked for Great Lakes by GLERL (Liu, Schwab et al) using obs

    • Made more accurate via wind analysis developed at GLERL

  • GLERL wave model is the main source of wave now/forecasts in the region today.


General Views: Modern Era

  • Early 2004: Pilot-test using WAVEWATCH III at Marquette WFO

    • Good results : proof of concept , 3G model could be beneficial

    • Motivation to WFOs request toward using WW3 in the region

  • Late 2004: Development o a WW3-based system starts

  • 2005: Testing and interaction with local WFOs

    • Defining best wave spectral resolutions

    • Assessing quality of available winds (ETA, then NAM model)

    • Gathering bathymetric data (NGDC and GLERL) => spatial grids


NCEP Op Implementations

  • 08/2006: Great Lakes Wave system (GLW)is made operational

    • 4 X daily forecasts at 00Z, 06Z, 12Z and 18Z

    • Initialization using 0h nowcast from previous run, with 6h hindcast forced with NDAS, then 84h forecasts

    • Output products made available via ftp://ftpprd.noaa.gov and non-operational NCEP website http://polar.ncep.noaa.gov


NCEP Op Implementations

  • 2008: Experimental GLW/NDFD (GLWN) wave system

    • Request from WFOs for a wave model forced with NDFD winds

  • 2009: Op implementation of the GLWN

    • Identical settings to GLW/NAM: shared spectral resolutions, spatial grids, ice coverage, air-sea temperature differences etc

    • Staggered operational schedule: 03Z, 09Z, 15Z and 21Z

    • Extended forecast horizon (up to 144h)

    • No hindcast: initialization with 6h forecasts of previous cycle


NCEP Op Implementations

  • GLW/GLWN system configuration:

    • WAVEWATCH III model

    • Wave evolution physics parameterizations following Tolman & Chalikov (1996), default WW3 package

    • Single, regular spatial grid covering all lakes

      • 0.05o x 0.035o resolution in longitude by latitude ~ 4km

    • Discrete wave spectrum resolved between 0.05Hz and 0.72Hz

      • Corresponds to the observed wave scales as per buoy data

    • Stability estimated internally using air-sea temperature differences

    • Products output every 3h, made available via NOAA’s operational ftp server and non-operational web site


Performance: Typical Conditions

  • Bulk validation: emphasizes performance in typical conditions

    • Wave model vs buoys: bias, RMS errors and correlation

  • Performance assessment made for years 2008 and 2009

  • Only NDBC buoys used for bulk performance study

    • Lake Superior: 45001, 45004, 45006

    • Lake Michigan: 45002, 45007

    • Lake Huron: 45003, 45008

    • Lake Erie: 45005

    • Lake Ontario: 45012

  • Assessment made relative to reference wave model for the region: GLERL wave model, Great Lakes Op Forecast System (GLOFS)

    • Forecast phase has same forcing winds as in the GLWN model


Performance: Typical Conditions

2009

Winds

24h

48h

Waves


Performance: Typical Conditions

  • Bulk validation in 24h and 48h forecasts

    • NAM and NDFD winds are very similar, almost indistinguishable

    • GLW, GLWN and GLERL have similar biases

    • GLW and GLWN have slightly lower RMS errors than GLERL

    • GLW and GLWN have noticeably better correlations than GLERL

  • Typical conditions: GLW, GLWN, GLERL are statistically similar

    • Generally similar values of bias, RMS error and correlations

  • Standard deviations are very different

    • Normalized STD for GLERL is close to 1 relative to buoys

    • GLW is close to 0.80, GLWN is close to 0.75!


Performance: Severe Sea States

  • 99% wind speeds and wave heights (normalized by obs)

    • Emphasize more severe sea states, storms

2009

Winds

24h

48h

Waves


Performance: Storm Wave Forecasts

  • Assessment included 95% (not shown) and 99% percentiles

  • Results reveal that:

    • NAM and NDFD provide a reasonable representation of stronger winds associated with storms

      • NAM slightly outperforms NDFD at upper wind-speed percentile

    • GLW, GLWN systematically underestimate upper Hs percentiles

      • GLW clearly outperforms GLWN

    • GLERL wave model provides a reasonably accurate representation of observed upper Hs percentiles

  • Both GLERL and GLWN use the same NDFD forecast winds

    • Default WAVEWATCH III physics are not doing a good job in reproducing wave growth in intense storms in areas with short/irregular fetches… nothing new.


Better Physics: Bridging the Gap

  • Recent WAVEWATCH III development focused on better parameterizations of wave evolution physics

  • ONR, USACE and NCEP joined forces in a NOPP

    • Scientists from USA, Canada, Netherlands, France, Australia etc

  • Collaboration that recently produced 1st improved wave physics package, in development version of WAVEWATCH III

    • Team spearheaded by FabriceArdhuin (Ifremer, France)

    • More realistic wave growth and dissipation source terms

    • Input based on Miles exponential growth

    • Negative input due to swells or mature waves

    • Dissipation based on recent empirical data


Better Physics: Bridging the Gap

  • Performance of WW3 + Ardhuin et al. (2010) physics [A+10]

    • Comparative assessment using GLERL wave model as a reference

    • To emphasize model skill, analysis winds were used

    • Wave hindcasts were generated with models forced by GLERL surface wind analyses for 2008 and 2009

    • GLW system was run with the default WW3 physics (Tolman and Chalikov, 1996) and with the new A+10 package

    • GLERL wave model data and GLERL wind analyses were provided by Dave Schwab and Greg Lang from … GLERL!


Better Physics: Bridging the Gap

2009

  • WW3 with A+10 Physics

    • Breakthrough-level improvement to GLW in term of Hs

    • Improved GLW’s already good bulk statistics (bias, RMS error, correlation)

    • Matched GLERL STD

    • Higher precision in tracking observations

    • Much improved wave periods relative to GLERL


Better Physics: Bridging the Gap

2009

  • 99% normalized by obs

  • GLERL wind analyses have a superb quality: great accuracy in upper wind speeds at 99%

  • WW3 with A+10 Physics

    • Breakthrough-level improvement in predicting 99%wave heights


Example Cases: Severe Sea States

  • Buoy 45004, Northeast of Marquette, MI (Lake Superior)

    • Double whammy…

  • September 28 2009

    • Maximum recorded wind speed: 18.25 m/s

    • Maximum recorded Hs: 5.15 m

      http://www.youtube.com/watch?v=2pKgF_QMT14

  • October 10 2009

    • Maximum recorded wind speed: 16.60 m/s

    • Maximum recorded Hs: 5.05 m

      http://www.youtube.com/watch?v=MRczx6Mr0gc


  • Example Cases: Lake Superior 2009


    Future Work

    • Extend cases to include more severe wave events

    • Expand assessment relative to Environment Canada Buoys

      • Towards development of a Great Lakes wave test bed

        • Including also “swell” cases

        • Wave evolution in sudden wind drop cases

        • Nearshore wave evolution (further down the track)

        • Collaboration with NWS WFOs, POC Greg Mann


    Future GLW/GLWN Systems

    • Great reaults, aren’t they??

    • Implement A+10 physics in GLW/GLWN within 1 year

    • Include in the new system several other upgrades:

      • Hindcast phase in GLWN using new RTMA overlake analyses

        • RTMA will have internal adjustment over lakes using GLERL wind analysis algorithm

      • More accurate bathymetries (current not updated since 2004)

      • Possibly higher overall grid resolution (probably double) ~ 2km

      • Deployment of nearshore grids, two-way nested to coarser grid, possibly at ½ km resolution

    • New GLW development to be made in tight collaboration with NWS Great Lakes WFOs.


    This is the last slide!

    QUESTIONS?

    If anything to say or ask later: [email protected]


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