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034
NOUS41 KWBC 051809
PNSWSH
PUBLIC INFO. STATEMENT...TECHNICAL INFORMATION NOTICE 00-12
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
210 PM EDT FRI MAY 5 2000
TO: FAMILY OF SERVICES /FOS/ SUBSCRIBERS...NOAA WEATHER
WIRE SERVICE /NWWS/ SUBSCRIBERS...OTHER NATIONAL
WEATHER SERVICE /NWS/ CUSTOMERS...NWS EMPLOYEES
FROM: LEROY SPAYD...CHIEF...SCIENCE AND TRAINING CORE
SUBJECT: CHANGES IN THE NATIONAL CENTERS FOR ENVIRONMENTAL
PREDICTION OPERATIONAL WAVE MODEL SUITE...EFFECTIVE MAY
10 2000
TWO CHANGES IN THE NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION
OPERATIONAL WAVE MODEL SUITE WILL BE IMPLEMENTED WEDNESDAY...MAY
10 ON THE 1200 UTC MODEL CYCLE RUN. THESE CHANGES IMPROVE THE
MODEL PREDICTIONS IN SHALLOW WATER AREAS...WHILE MAINTAINING
SUPERIOR FORECASTS IN THE OPEN OCEAN. THE CHANGES AFFECT ALL
MODELS BASED ON THE STATE-OF-THE-ART NOAA WAVEWATCH III MODEL
WHICH INCLUDES GLOBAL (NWW3)...ALASKA WATERS (AKW)...AND WESTERN
NORTH ATLANTIC (WNA) DOMAINS.
ONE CHANGE FIXES THE SEEDING ALGORITHM IN THE MODEL. WHEN THE
WIND DIES AND THE SPECTRAL ENERGY PRODUCES NO NOTICEABLE
WAVES...THIS ALGORITHM KEEPS ENOUGH ENERGY AVAILABLE TO GROW THE
WAVE SPECTRUM REALISTICALLY WHEN THE WIND RETURNS. BUT...AS
WRITTEN IN THE MODEL SOFTWARE...THE ALGORITHM SOMETIMES FAILED TO
PUT THE SEED ENERGY IN THE CORRECT PORTION OF THE SPECTRUM...AND
THE MODEL SOMETIMES FAILED TO GENERATE WAVES QUICKLY ENOUGH WHICH
LEAD TO A CONDITION KNOWN AS FLATLINING'. THIS CONDITION HAS
BEEN CORRECTED SO THE ALGORITHM WILL ALWAYS PUT SEED ENERGY IN
THE CORRECT PORTION OF THE MODEL SPECTRUM. THE EFFECTS OF THIS
FIX ARE SYSTEMATICALLY POSITIVE IN THE MODEL SUITE...BUT ARE
CONFINED TO THE GULF OF MEXICO...U.S. EAST COAST...DAVIS
STRAITS...BERING SEA...AND BEAUFORT SEA AS WELL AS OTHER AREAS
OUTSIDE DIRECT U.S. INTERESTS. THE EFFECT IS LARGEST IN THE WNA.
THE OTHER CHANGE WAS MADE BECAUSE THE WAVES NEAR THE MISSISSIPPI
GULF COAST WERE STILL SYSTEMATICALLY LOW EVEN WITH THE POSITIVE
RESULTS FROM THE CHANGE TO THE SEEDING ALGORITHM. THIS SUGGESTED
AN OVER-ESTIMATION OF ENERGY LOSS DUE TO BOTTOM FRICTION. SO THE
BOTTOM ROUGHNESS WAS REDUCED SOMEWHAT WHICH RESULTED IN GENERALLY
POSITIVE RESULTS IN SHALLOW WATER AREAS. THIS IS PARTICULARLY
TRUE IN THE GULF OF MEXICO. THERE ARE SOME NEGATIVE IMPACTS IN
DEEPER WATER IN THE EASTERN BERING SEA AND IN THE BAHAMA ISLAND
CHAIN WHERE MANY OF THE ISLANDS ARE NOT RESOLVED IN THE WNA.
THESE NEGATIVE IMPACTS ARE HIGHLY LOCALIZED...AND THE POSITIVE
IMPACTS FAR OUTWEIGH THE FEW NEGATIVE IMPACTS THAT HAVE BEEN
NOTED.
FOR ADDITIONAL INFORMATION AND TEST RESULTS SEE:
HTTP://POLAR.WWB.NOAA.GOV/WAVES/MOD/SEED/ ...AND
HTTP://POLAR.WWB.NOAA.GOV/WAVES/MOD/BOT1/
/USE LOWER CASE/
END
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