Notice of Intent to Change the NCEP AVN/MRF Forecast System
Brief description of change(s):
1) Minor corrections are made to gravity wave drag, random cloud types in the
convection, and evaporation with trace snow on the ground.
2)Small modification to auto-conversion rate for ice is done to reduce light
precipitation. Effective radius for ice crystals is calculated empirically
based on observations of Heymsfield and McFarquhar (1996). Evaporation of
falling precipitation is also slightly increased. Critical relative humidity
for condensation is now made to be a function of resolution.
Reason for Change(s):
During testing of the package we implemented in May 2001, several minor coding
bugs were discovered. These bugs were not fixed in the package to ensure that
clean tests were done for extended period of time. Tests were done after the
implementation and we found no major impact to these changes. We are now ready
to fix the minor errors in the model. In addition, slight tuning of the cloud
and radiation parameters have also been done to correct biases we found with
the new cloud parameterization scheme.
Schedule for change:
Final testing completed: completed July 2001.
CAFTI approval : not required'
Expected implementation : 14 August 2001.
Description of testing:
Statistical summaries :
http://sgi62.wwb.noaa.gov:8080/STATS/STATS.html
Forecast examples :
http://sgi62.wwb.noaa.gov:8080/STATS/MAPS.html
Anticipated impact on forecasts:
Improvement of the spin up characteristics in the tropics. Stronger tropical
storm are maintained in the forecasts. Slightly less precipitation bias over
mid-latitude land area.
Human point of contact for further information:
Pete Caplan (301-763-8000 ext 7229, peter.caplan@xxxxxxxx)
Field Evaluation:
We have been working with the NCEP HPC and TPC forecasters and the forecaster
response have generally been positive.
Approvals:
EMC Director: Stephen J. Lord Date: 7 August 2001