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872
NOUS41 KWBC 070200
PNSNMC
NATIONAL TECHNICAL INFORMATION MESSAGE 96-5
NATIONAL WEATHER SERVICE HEADQUARTERS WASHINGTON DC
200 PM EST WED FEB 7 1996
TO ALL USERS OF NWS PRODUCTS
FROM JOSEPH R. BOCCHIERI...CHIEF... SCIENCE AND
TRAINING CORE
SUBJECT CHANGES TO THE OPERATIONAL EARLY ETA MODEL
(THE FOLLOWING INFORMATION WAS PROVIDED BY GEOFF DIMEGO)
AT 1200 UTC 31 JANUARY 1996 THE FORECAST MODEL CODE AND
POST-PROCESSOR USED FOR THE OPERATIONAL EARLY ETA MODEL RUN WERE
CHANGED TO BE IDENTICAL WITH THE CODES NOW RUNNING THE MESOSCALE
ETA MODEL. THE MAIN REASON FOR THIS CHANGE WAS TO AVOID THE
OCCASIONAL NON-REPRODUCIBLE FAILURES THAT WERE OCCURRING WITH THE
ORIGINAL EARLY ETA VERSION. SINCE NCEP'S AVAILABLE RESOURCES ARE
LIMITED AND THE PROSPECT OF QUICKLY FINDING THE SOURCE OF THE
ERROR WERE SLIM... THE DECISION WAS MADE TO IMPLEMENT THE MESO
ETA CODE WHICH HAS BEEN RUNNING WITHOUT FAILURE SINCE JULY. THE
CONFIGURATION OF THE EARLY ETA REMAINS 48 KM AND 38 LEVELS WHILE
THE MESO ETA RUNS AT 29 KM AND 50 LEVELS. THE CONTENT AND
TIMELINESS OF CURRENT ETA MODEL PRODUCTS AVAILABLE ON THE OSO
SERVER AND THE NOAA INFORMATION CENTER ANONYMOUS FTP SERVER
(NIC.FB4.NOAA.GOV) REMAINS UNCHANGED.
AS A RESULT OF THIS MODEL CODE CHANGE... TWO AREAS OF THE
ETA MODEL'S PARAMETERIZED PHYSICS HAVE BEEN UPGRADED AS DESCRIBED
BELOW.
1) LAND-SURFACE PHYSICS: A TWO-LAYER SOIL MODEL WITH A
VEGETATION CANOPY HAS BEEN ADDED TO THE ETA MODEL'S SURFACE
PHYSICS PACKAGE. THIS SURFACE MODEL IS CAPABLE OF SIMULATING
THE SEASONAL EVOLUTION OF EVAPORATION AND SOIL MOISTURE. IN
ADDITION... A NEW SURFACE PARAMETERIZATION SCHEME WAS INTRODUCED.
HENCE... SOIL MOISTURE AND SOIL TEMPERATURE ARE EXPLICITLY
FORECAST IN THE TWO SOIL LAYERS... ALONG WITH A SURFACE SKIN
TEMPERATURE BASED ON THE SURFACE ENERGY BALANCE. EVAPORATION IS
COMPRISED OF A) DIRECT EVAPORATION FROM THE SOIL SURFACE...
B) DIRECT EVAPORATION FROM WET VEGETATION... AND C) TRANSPIRATION
THROUGH THE VEGETATION CANOPY.
2) TURBULENT VERTICAL TRANSPORTS: THE COMPUTATION OF
TURBULENT KINETIC ENERGY HAS BEEN REVISED. THE PERFORMANCE OF
THE SCHEME IS IN REASONABLE AGREEMENT WITH OBSERVATIONS AND
SHOWED NO ADVERSE IMPACT WHEN TESTED IN PARALLEL ETA MODEL RUNS.
BASED ON MODEL CASE STUDIES... RETROSPECTIVE PARALLEL TESTING...
AND CONCURRENT PARALLEL TESTING... THE FOLLOWING CHANGES SHOULD
BE EXPECTED IN THE EARLY ETA FORECASTS
- IMPROVED SURFACE HEATING AND EVAPORATION AND SKIN
TEMPERATURES
- IMPROVED SOIL MOISTURE EFFECTS (E.G. DRYLINE)
- IMPROVED CONVECTIVE STABILITY INDICES
- IMPROVED DIAGNOSIS OF 2-M TEMPERATURE AND 10-M WINDS
- IMPROVED PRECIPITATION SKILL SCORES WITH AN APPROXIMATE
20% INCREASE IN PRECIPITATION BIAS
- SMOOTHER TIME EVOLUTION OF TURBULENT MIXING
- IMPROVED FORECASTS OF SURFACE RUNOFF OF RAINFALL
- IMPROVED DIURNAL EVOLUTION OF BOUNDARY LAYER STRUCTURE
RESULTING IN A REDUCTION OF THE COLD BIAS NEAR THE TOP
OF THE BOUNDARY LAYER (APPROXIMATELY 850 MB)
FOR ADDITIONAL DETAILS OR QUESTIONS ON THE CHANGES IN THE
EARLY ETA MODEL...PLEASE CONTACT GEOFF DIMEGO OF THE NATIONAL
CENTER FOR ENVIRONMENTAL PREDICTION AT 301-763-8056.
IF YOU HAVE ANY CONCERNS RELATED TO POSSIBLE IMPACTS OF THE
CHANGES IN THE EARLY ETA MODEL... PLEASE CONTACT BRENT BOWER OF
THE OFFICE OF METEOROLOGY AT 301-713-1970.
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