From: ccm@sage.cgd.ucar.edu (CCM Group Directories)
Message-Id: <199410131948.NAA07372@grub.cgd.ucar.edu>
Subject: Re: HELP
To: fan@meteor.atms.purdue.edu (Zengquan Fan)
Date: Thu, 13 Oct 94 13:48:37 MDT
In-Reply-To: <9410122123.AA17652@meteor.atms.purdue.edu>; from "Zengquan Fan" at Oct 12, 94 4:23 pm
>Problem w/CCM2 Perpetual Run Simulations!!
> - We recently ran a perpetual run using January initial conditions with
> the intent of running out about 400 days; thus, the only difference from
> the original code is that we flipped the switch from seasonal to perpetual
> mode!! After approximately 50 days the model blows up, indicating that we
> have incorrect values for specific humidity which we definitely do as the
> model outputs negative specific humidity values!? Upon closer inspection,
> the error comes about due to a sudden, dramatic increase in the global
> RMS divergence, which we feel is probably due to an anomalous regional
> increase in surface convergence in the tropics (this may not be confined
> to tropics but just happens to be where the model bombs on us; 35th long.
> and 37th lat. parallel). The anomalous convergence field leads to a huge
> perturbation in the vertical velocity field, resulting in a violation
> of the vertical CFL condition in the model!! In turn, in the subsequent
> time step the horizontal CFL condition is violated(dramatically) and the
> global rms. temp rises by 25K, presumably in response to ridiculously
> large condensational heating. The negative 'Q' values result from
> excessive condensation as more water vapor is condensed than is actually
> available in the local atmospheric column. So it is undoubtedly a
> positive feedback loop, probably kicked off by an anomaly in the near sfc.
> horizontal wind field, which screws up the div. field, etc., etc...
> Has anyone encountered this before? Is it something specific to
> a perpetual simulation??
==============================================================================
As we have indicated in previous messages, an integral component of
the CCM2 is the User's Guide documentation (NCAR/TN 379+IA, available
in postscript format from the NCAR CGD Gopher) which clearly and
completely identifies the available namelist options. ANNCYC is NOT
one of the documented namelist options, and by definition should be
presumed not to work. There are several other undocumented "optional"
configurations appearing in the model code. One can think of these as
"hooks" intentionally left in the model for the convenience of the
developers, and other knowledgable users who might want to modify the
documented configuration to address their particular needs. The mere
existence of these hooks, however, does not imply that they work in
any way.
Enabling a perpetual-mode capability involves the modification of
several CCM2 modules, most importantly the routine that computes
surface/sub-surface temperature change, and the routine that handles
Julian day evaluation for sun angle calculations. The particular
details of a perpetual implementation are a function of end-user
needs, and hence are the responsibility of the end-user.
CCM Core Group
(0)