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PUBLIC INFO. STATEMENT...TECHNICAL IMPLEMENTATION NOTICE 99-08
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
1130 AM EDT THU MAY 13 1999
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 TO THE NCEP OPERATIONAL ETA MODEL SYSTEM
AT 1200 UTC 13 MAY 1999 THE 3-D VARIATIONAL (3DVAR) ANALYSIS
USED IN THE OPERATIONAL ETA MODEL RUNS (00Z...03Z...12Z AND 18Z)
AND USED IN THE ETA DATA ASSIMILATION SYSTEM (EDAS) WAS CHANGED
TO CORRECT PARAMETERS INFLUENCING THE BALANCE BETWEEN THE
ANALYZED MASS AND WIND FIELDS. IN NOVEMBER 1998...THESE
PARAMETERS WERE ADJUSTED IN SUCH A WAY AS TO DRAW MORE CLOSELY
FOR RADIOSONDE DATA BUT THIS ADJUSTMENT HAD THE NEGATIVE EFFECT
OF PRODUCING MUCH WEAKER BALANCE BETWEEN MASS AND WIND ANALYSIS
FIELDS. THIS OCCURRED PRIMARILY IN REGIONS WITH MOSTLY SINGLE
LEVEL OR SINGLE TYPE DATA (E.G. SATELLITE TEMPERATURE PROFILES...
FLIGHT-LEVEL AIRCRAFT DATA OR SATELLITE CLOUD-DRIFT WINDS). THE
RESULT WAS FREQUENT POOR ETA ANALYSES ESPECIALLY OVER OCEANIC
REGIONS AND POOR FORECASTS ESPECIALLY AT LONGER RANGES. THE
CORRECTED 3DVAR PRODUCES MORE BALANCED MASS AND WIND ANALYSES AT
SLIGHT EXPENSE OF THE INITIAL FIT TO RADIOSONDE DATA. TESTS OF
THE CORRECTED 3DVAR ANALYSIS PRODUCED MUCH HIGHER FORECAST
ACCURACY.
FURTHER DETAILS ON THIS CHANGE CAN BE FOUND AT :
HTTP://WWW.NWS.NOAA.GOV/OM/TPB/3D-ETA.HTM /LOWER CASE/
IF YOU HAVE FURTHER QUESTIONS...CONTACT
GEOFFREY J DIMEGO
NATIONAL CENTERS FOR ENVIRONMENTAL PREDICTION
ENVIRONMENTAL MODELING CENTER
MESOSCALE MODELING BRANCH
NWS OFA ROUTE: W/NP22
5200 AUTH RD 207 WWBG
CAMP SPRINGS MD 20746-4304
(301)763-8000 X7221
INTERNET ADDRESS: GEOFF.DIMEGO/AT SIGN/ NOAA.GOV
THIS AND OTHER NOTICES ARE ON THE INTERNET AT
HTTP://WWW.NWS.NOAA.GOV/OM/NOTIF.HTM /LOWER CASE/
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