[ferret_users] Lesson, be careful with data only defined above a surface Re: [ferret_users] How to project 3D data onto an arbitrary 2D surface?

[Lev Tarasov <lev@xxxxxx>]

Thanks to Steve's suggestion to plot the fields in the YZ plane, I 
identified the problem as the field I was projecting was only defined 
above the surface. So when downscaling model output to a surface, check 
that the field fully intersects the surface.

Lev

Lev Tarasov -   Dept of Physics and Physical Oceanography,
		Memorial University of Newfoundland.
                email: lev@xxxxxx
                http://www.physics.mun.ca/~lev/
		Tel (709)-737-2675
		Fax (709)-737-8739

On Wed, 15 Apr 2009, Steve Hankin wrote:

> At a glance it looks correct.  The trick may be to visually inspect each of 
> the fields to spot the problem.  For example, if Z[g=Thz] and HSFC were in 
> different units?  The checkerboard that you're describing would be consistent 
> with the idea that the zeroh and kernel fields weren't "smooth".  You should 
> be able to see this using the LIST command.  Pick a fixed X, for example, and 
> LIST the kernel field in the YZ plane.
>
> If this leads you to an answer, please report it to the email group to close 
> the question.
>
>   - Steve
>
> Lev Tarasov wrote:
> > Hi;
> >     I have a 4D temperature field (TFIELD below), and I want to project it 
> > onto a surface topography defined by HSFC(i,j)
> >
> >  name     title                             I         J         K 
> > L
> >  LEV      level (-999 is surface)          1:8       ...       ... 
> > ...
> >  HSFC     Surface topography               1:128     1:64      ... 
> > 1:12
> >  TFIELD   Level temperature                1:128     1:64      1:8 
> > 1:12
> >  HFIELD   Level altitude                   1:128     1:64      1:8 
> > 1:12
> >
> > Finding the closest analogue in the FAQ, I tried used @WEQ, but this did 
> > not work (the surface temperature turned into a checkerboard of 
> > discontinuous values). Specifically, I did the following:
> >
> > 1) transform from native pressure levels to a height grid:
> >
> > define AXIS/Z=-50:5500:50 /UNIT=meters zha
> > LET Thz  = ZAXREPLACE(TFIELD,HFIELD, z[gz=zha])
> > !plots of this looked good
> >
> > 2) project onto HSFC surface height field:
> >
> > set mode interp
> > let zeroh=Z[g=Thz]-HSFC
> > LET kernel = zeroh[Z=@WEQ:0]
> > LET integrand = kernel*Thz
> > Let Ts=integrand[Z=@SUM]
> > !plots of Ts were nuts
> >
> > What's the simplest way to do this correctly?
> >
> > thanks,
> >
> > Lev
> >
> >
> >
> > Lev Tarasov -   Dept of Physics and Physical Oceanography,
> >         Memorial University of Newfoundland.
> >                 email: lev@xxxxxxxxxxxxxx