[RegCNET] Bug in: IMPORTANT - "BUG" FOUND IN REGCM3 - PLEASE READ

[Bridget Thrasher]

If anyone is running from non-6-hourly driving data, I believe the  
equation below will not give you the proper timing for the incoming  
solar radiation. Instead of using the ibdyfrq setting from the  
regcm.in file, calday appears to be hard-coded to every 6 hours  
(dividing by 4). This same equation is also found in solar1.F, and the  
(NNNNNN-NSTRT0)/4. portion is in an equation in lakedrv.F.

-Bridget

------------------------------------------------
Bridget Thrasher
PhD Candidate
Earth & Planetary Science Dept
UC Santa Cruz





On May 23, 2007, at 5:30 AM, FILIPPO GIORGI wrote:

> Dear RegCNETers
>
> With this email I wanted to alert you that, thanks to Jonathan, we  
> have
> found a bug in the current RegCM code. If you have it in your code,  
> you
> need to correct it.
>
> The bug is in the calculation of the eccentricity in subroutine  
> getdat.f.
>
> More specifically, the line of code
>
>       calday = dble(julday)+mod(NNNNNN-NSTRT0,4)/4.+(xtime/60.+gmt)/ 
> 24.
>
> should be replaced with
>
>       calday = dble(julday)+(NNNNNN-NSTRT0)/4. + (xtime/60.+gmt)/24.
>
> The bug sets the eccentricity at the value of the initial day  
> (idate0 in
> regcm.in) and then does not change it any more.
>
> So, for example, if you started your run on Jan 1, the eccentricity  
> will
> remain that of Jan 1 for the whole run. The eccentricity affects the  
> value
> of solin, i.e. the incoming solar radiation at the top of the  
> atmosphere.
> This values varies by about 6-7% from a maximum in January to a  
> minimum in
> July. So, depending on when you start your simulation and how long  
> it is,
> you might have an error of up to 6-7% in the incoming solar radiation.
> This may be more or less important for your simulation, but you need  
> to
> change it and check older runs. If you completed only short runs (say
> 3-months or so), the bug should not affect your simulations much.  
> Also, in
> the winter we do not expect a big effect. The largest effect is for  
> the
> summer climate in a long run started in January, when summer solar
> radiation is too high by up to 6-7%.
>
> Unfortunately, we are not sure of when this bug was put into the  
> model,
> but we suspect it has been there for some time, probably since a  
> late 2004
> version. It also seems that it is not in all versions of the model  
> that
> have been circulating since then, both serial and parallel versions,  
> so
> you need to check yours. In fact, if you have any idea of why, when  
> and
> how this code change was put in, please let us know, so that we can  
> try to
> figure out what happened.
>
> Note that the code in the public website has been already updated and
> corrected, so you can also check there how to remove the bug.
>
> In the process of checking this, we also found that, for reasons too  
> long
> to explain, you should always start your run on 00:00 GMT, otherwise  
> the
> model has some problems in calculating the declination angle with the
> proper timing. Fortunately the model routinely starts at 00:00 GMT,  
> but
> anyways you should be aware of this, especially because we have not  
> been
> able to correct this problem (we are working on it).
>
> It is unfortunate to find such bugs, but it happens. It is part of
> the modeling life, although certainly not a nice part.
>
> Should you have any questions, or any comments that might help us
> understand what happened, do not hesitate to contact me, Bi, or Sara.
>
> best regards,   Filippo Giorgi
>
> ################################################################
> # Filippo Giorgi, Head                                         #
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