# [IDV #ANI-315803]: calculation of perturbations using SAVS-like function (GEMPAK)

• Subject: [IDV #ANI-315803]: calculation of perturbations using SAVS-like function (GEMPAK)
• Date: Wed, 03 Mar 2010 08:06:03 -0700

```Hey Cory-

Hope you are doing well.

So, it's only been a few months, but I finally implemented the SAVG
function in the IDV.  It's in today's nightly build.

> Ok...it's much much later today :-)...dumb question...what is the function
> SAVG?, I know of AVG(s1,s2) but never came across savg?

I'm not sure what the difference is between SAVG and SAVS.  The docs just say
that SAVS works on a subset.  In the IDV, you would just use SAVG and subset
the grid using the map subset in the properties.  I only implemented an savg
procedure for the formulas.

You should now be able to use the Grids->Create a grid diagnostic formula and
put in:

sub(u,savg(u))

and then choose the U component when prompted for a parameter (or whatever else
you want to do).

Don Murray
________________________________________
> From: Unidata IDV Support [address@hidden]
> Sent: Wednesday, August 12, 2009 6:31 PM
> To: Joshua C Demko
> Cc: address@hidden; Joshua C Demko
> Subject: [IDV #ANI-315803]: calculation of perturbations using SAVS-like
> function (GEMPAK)
>
> Hi Cory-
>
> > I'm getting slower and slower with these responses...not good...maybe I
> > just need a beer.
>
> No problem.  I haven't had time to look at this.  We start the IDV training
> workshop tomorrow so I've been getting ready for that.
>
> Anyway...the mean is across 1 time step (mean for one forecast output time
> i.e. 1 hour for me). As for the GEMPAK code...I use the function below
> >
> > GFUNC    = sub(un(wnd),savs(un(wnd)))
>
> What does savs give you over savg.  Are you subsetting by region or by level?
>
> > This function I use in GDCROSS where I set my CXSTNS equal to my lat;long
> > of the endpoints. So as I read this, I am subtracting the mean u component
> > calculated on each pressure surface along the crossection I defined from
> > each u.
>
> Okay, I understand what you are trying to do now.
>
> I check this with what I obtain in IDL and both agree. At this stage in my
> life, if I get just 2 things to agree I'm stoked (I totally ignore if both
> precedures are incorrect in the same way!!).
> >
> > I have attached a figure which shows several crossectional averages for
> > different parameters (only need to focus on the black contour lines with
> > show u(prime). I would like to do this in IDV only show a 3D image of u'
> > (and other parameters) over the mountain. Essentially a 3D box over the
> > mountain to show which levels/sides are contributing more to
> > convergence/divergence .
> >
> > whew.....that's alot...anything else you need on your end?
>
> That'll do it (except for the savs vs savg question above).
>
> We'll put this request on the TODO list.  We've got a lot of other things on
> the list right now (like reading GEMPAK point/sounding files), but we might
> be able to sneak it in at some point.  The hard part will be to do an average
> at each level instead of over the entire volume, but that's just an index
> space thing.
>
> Don
>
> > ________________________________________
> > From: Unidata IDV Support [address@hidden]
> > Sent: Tuesday, July 28, 2009 8:34 AM
> > To: Joshua C Demko
> > Subject: [IDV #ANI-315803]: calculation of perturbations using SAVS-like
> > function (GEMPAK)
> >
> > Hi Cory-
> >
> > > Full Name: Cory Demko
> > > Organization: UWYO
> > > Package Version: 2.7b3 build date:2009-06-16 07:07 UTC
> > > Operating System: Windows XP
> > > Hardware: Java: home: C:\Program Files\IDV_2.7b3\jre version: 1.6.0_11
> > > j3d:1.5.2 fcs (build4)
> > > Description of problem: Don:
> > >
> > > Sorry for the delay...decided to make a new support email...to answer
> > > your question, I am looking at calculating the mean u component along a
> > > constant pressure surface to determine u' along the same pressure...I
> > > will then make a cross section of u'...for each timestep...
> >
> > And sorry for our delay.  There is no method to do this in the IDV
> > currently, but we are thinking about adding this capability.  So, I have a
> > couple of questions:
> >
> > - is the mean across all timesteps, or for each timestep?
> > - can you send me instructions on how you would do this in GEMPAK?
> >
> > Don
> >
> >
> > Ticket Details
> > ===================
> > Ticket ID: ANI-315803
> > Department: Support IDV
> > Priority: High
> > Status: Open
> >
>
>
> Ticket Details
> ===================
> Ticket ID: ANI-315803
> Department: Support IDV
> Priority: High
> Status: Open
>

Ticket Details
===================
Ticket ID: ANI-315803
Department: Support IDV
Priority: Critical
Status: Open

```