Re: [gembud] Possible bug in ensemble functionality with precipitation

Hi, Pete,

Try summing as follows:  ens_ssum(mul(gt(p03i,0),p03i)).  This will keep
any negative values out of the summation.


On Mon, Dec 10, 2012 at 4:23 PM, <pmanousos@xxxxxxxxxxxxxxxxxxx> wrote:

> Greetings.  We believe we may have found a bug when using the cumulative
> precipitation functionality with ensemble functions in GEMPAK gridded
> programs.
> We are wondering if this is a known bug and if not wanted to bring it to
> the user communities attention.  Any thoughts welcome.  Details below.
> Pete
> *Reference the Attached Images*
> Values plotted are scaled ("scale=2") QPF from the 03Z SREF Dec 10 2012
> run using gdplot3 for "gdfile = {sref | 03}"
> *1. 2012121003f24_sref_p03i_ens_ssum.gif*
> Sum of all 21 members 3h QPF predictions at f24 using
> "gdpfun=ens_ssum(p03i)".  Note the values of "339" in near Philadelphia and
> "5" near Cincinnati.
> *2. 2012121003f27_sref_p03i_ens_ssum.gif*
> Same as #1, but for f27.  Note the values of "171" in near Philadelphia
> and "2" near Cincinnati
> *3. 2012121003f27_sref_p06i_ens_ssum.gif*
> One would expect a 6hr total of 510 at Phili and 7 at Cinci.  However
> using "gdpfun=ens_ssum(p06i)" at f27 yields negative values in Cinci (but
> expected values at Phili).
> Our concern is that with light precipitation events (especially if
> converted via precip type - say like freezing rain) the functionality as
> invoked above will yield erroneous results.
> *Additional Findings and Information*
>    - Using GEMPAK 6.4.0 on x64 system running RHEL 6.2
>    - Confirmed error also occurs with GEMPAK 6.2.0 gempak gridded programs
>    - Confirmed error occurs for either a p06i or p06m
>    - Confirmed error occurs for any given SREF run
>    - Confirmed each member being referenced by the ensemble function
>    "ens_ssum" has valid data at each grid point
>    - Confirmed error does NOT occur when applied to single members
>    (models).  Example - no such error occurs when "GDFILE = nam | 12" and
>    "gdpfun = p06i" for any given fhr)
>    - All members were pulled in from NOMADS and processed using NAGRIB2
>    - By the way we were using the "ens_ssum" to verify the wierdo results
>    we found using ens_savg -- which is how we found this bug
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