Subject: (none)
From: Phil Rasch (pjr@cgd.ucar.edu)
Date: Thu Apr 10 1997 - 15:06:07 MDT
Gerhard Gross wrote....
> Dear CCM users,
>
> I often get warning messages when I transport chemical
> species as tracers in CCM3, such as HNO2. The messages
> look like this:
>
> > WARNING: fixer for tracer 4 exceeded 0.10000 for
> > 4 points at k,lat = 17 27 Avg/Worst = 1.41335E-01 1.91718E-01
>
> They occur because of large concentration gradients of the
> tracer in certain areas of the model atmosphere. My question is
> whether I should override the fixer limit 'corm' in linemsbc.F
> which is currently set to 0.1? How much 'fixing' (mass adjustment)
> does the SLT transport scheme need?
It has been my philosophic assumption (and so far this has proven to
be valid) that the fixer should be cosmetic in nature, and that if it
is not then it should be disabled for those points. This is what is
happening when that error message is occuring. This of course
implies when it is turned off that mass conservation errors will occur
in the simulation.
I dont like the need to invoke the fixer at all, but right now it is
the only game in town. I generally see it only in two situations
1) during the first day of a simulation when the tracer field is
spinning up.
2) if I have near point sources in the emissions.
I dont worry about it at all in case 1). The model will soon settle
down and the fixer will decrease in importance. In case 2) I try to
assess its importance to the properties of the simulation. So far I
have managed to convince myself that except in the vicinity of the
point source it is not doing much to the simulation.
All this text does not answer your question precisely, cause I dont
think there is one correct answer. The best answer to the question you
have asked is that one should try and assess the simulation in terms
of the balance of processes. And if the fixer is important to the
simulation, you should turn it off, and this will imply that the model
will not conserve global mass precisely.
Phil Rasch
>
>
> ---- If you walk in the jungle don't act like prey! ----
>
> *****************************************************************
> Gerhard W. Gross gery@global.phy.pdx.edu
> Global Change Research Center or jh6gg@odin.cc.pdx.edu
> Portland State University
> *****************************************************************
>
>
>
-- Phil Rasch(National Center for Atmospheric Research, 303-497-1368) internet: pjr@ncar.ucar.edu, pjr@ucar.edu FAX: 303-497-1324
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