Experiment Name: Eta-32 with new radiance processing and modified cloud microphysics, EDAS precipitation assimilation, gauge adjustment of Stage IV precip analyses, and new radiation physics
|2003/10/24/00||Ferrier, H.-M. Lin||
|2003/10/10/12||Ferrier, H.-M. Lin||
In the case of snow, surface moisture flux now accounts for snowcover patchiness, with evaporation (sublimation) from the snowpack (weighted by the snowcover fraction), and surface evaporation (canopy evap, bare soil, transpiration) elsewhere (weighted by 1-snowcover fraction).
At each physics time step, ADJPPT computes the beginning and ending time of the time step to determine how much of the observed hourly rainfall should be from this time step. If this timestep falls entirely within an hour, then this amount is simply
hourly rainfall * (length of phys time step in sec)/3600.
The (length of physics time step in sec)/3600. is the 'time step as fraction of the hour'.
If this timestep straddles two different hours, we need to compute the amounts of time from each of the two hours that this time step is consist of, i.e. 'fraction1' and 'fraction2', then use these two amounts to compute how much each hour's observed precipitation contributes to the amount of precipitation falling into this time step.
In the 32-km control EDAS, fraction2 was not computed correctly because the fix which was placed in the production 12-km EDAS was inadvertently left out of the 32km version of the new Eta forecast code implemented in July 2003. In the case of the 32km eta parallel, where the physics time step is 540 seconds, during the timestep that straddles the 1st and 2nd hours (3,240 sec to 3,780 sec) fraction1 and fraction2 should be 0.1 and 0.05, respectively, but computed by the old executable, fraction2=0.90. In the 2003092812 ETAV run, during the first EDAS segment, precip obs at the 'test point' was 4.6mm and 10.4mm, respectively, so the amount falling between this timestep (3,240 sec to 3,780 sec) should be 0.98mm; but with the incorrect 'fraction2', the amount allocated to this timestep was 9.82mm.
Page Last Modified: October 30, 2003