Re: [ferret_users] how to control domain of mode INTERP without awkward file writing/reading

[Lev Tarasov <lev@xxxxxx>]

Hi Russ;

> I take it that H and Hw are on different grids (space?,time?) and that is why
> you are using the set interpolate mode. I think the problem is that

	H and Hw are on the same grid (see below). I also tried all the 
following 3 variants you suggested, and they had no impact:
 LET mask_grounded = if H*rhoI/rhoO gt Hw[g=H@AVE] then 1 else 0
 LET mask_grounded = if H*rhoI/rhoO gt Hw[g=H@LIN] then 1 else 0
 LET mask_grounded = if H*rhoI/rhoO gt Hw[g=H@MIN] then 1 else 0

I need set mode INTERP to interpolate from the 40km model grid to the 
location of the observational data. However, that causes the mask to
take fractional values which breaks the event crossing algorithm:

yes? stats mask_grounded
             IF H*RHOI/RHOO GT HW[G=H@MIN] THEN 1 ELSE 0
             LONGITUDE: 143.1E (interpolated)
             LATITUDE: 66.5S (interpolated)
             T: -120.05 to 0.05
 Total # of data points: 1201 (1*1*1*1201)
 Minimum value: 0
 Maximum value: 0.46
 Mean    value: 0.23324 (unweighted average)

So how can I keep set mode INTERP but have mask_grounded only
take on values 1 and 0?

Cheers,

Lev


yes? show grid Hw
    GRID (G001)
 name       axis              # pts   start                end
 XLONA1    LONGITUDE          360mr   0.5E                 0.5W
 YLATA5    LATITUDE            75 r   89.75S               52.75S
 normal    Z
 T120K100YR T                1201 r   -120                 0
yes? Show grid H
    GRID (G001)
 name       axis              # pts   start                end
 XLONA1    LONGITUDE          360mr   0.5E                 0.5W
 YLATA5    LATITUDE            75 r   89.75S               52.75S
 normal    Z
 T120K100YR T                1201 r   -120                 0


Lev Tarasov -   Dept of Physics and Physical Oceanography,
		Memorial University of Newfoundland.
                email: lev@xxxxxx
                http://www.physics.mun.ca/~lev/
		Sabbatical Tel (519)-821-3555
		Fax (709)-864-8739

On Thu, 8 Aug 2013, Russ Fiedler wrote:

> Hi Lev,
>
> I take it that H and Hw are on different grids (space?,time?) and that is why 
> you are using the set interpolate mode. I think the problem is that 
> interpolations are being performed by ferret in places and at times where you 
> don't expect it.
>
> I would explicitly regrid variables to a common grid and avoid any ambiguity.
>
> Changing your mask definition to
>
> LET mask_grounded = if H*rhoI/rhoO gt Hw[g=H@AVE] then 1 else 0
> or
>  LET mask_grounded = if H*rhoI/rhoO gt Hw[g=H@LIN] then 1 else 0
> or maybe some other like @MIN may make sense.
>
> That should allow you to run with interpolate mode off.
>
>
> Cheers,
> Russ
>
>
>
> On 08/08/13 01:42, Lev Tarasov wrote:
> > I have a routine to figure out the time when a location last becomes free 
> > of grounded ice (ie for comparing model results to data for the last 
> > glacial cycle Antarctic ice sheet). To figure out whether the ice is 
> > floating, we need to use mode INTERP. However, this ends up messing up the 
> > @EVNT algorithm for finding out when the last crossing (in this case 
> > ungrounding of ice) occurs., ie: in the below, with mode interp on, 
> > mask_grounded (= if H*rhoI/rhoO gt Hw then 1 else 0) ends up with 
> > fractional values.
> >
> > set region/x=143.14 /y=-66.48
> > ! H and Hw are 2D space + 1D time fields
> > LET rhoI = 910  ![kg/m3]
> > LET rhoO = 1028 ![kg/m3]
> > LET mask_grounded = if H*rhoI/rhoO gt Hw then 1 else 0
> > LET grounded_event=mask_grounded[T=-120:0@EVNT:1]      ! find all the
> >         instances when ice grounded (this starts at -120, incrementing for 
> > each event)
> > LET last_event = grounded_event[T=@max]                ! find the value of 
> > the last event
> > LET mask_last = IF grounded_event EQ last_event THEN 1 ! make a mask based 
> > on last event value, ie domain with event value = last value
> > LET idx= mask_last[T=@LOC:1]                           ! get the index of 
> > the first value in the mask \ie the last grounded event
> > LET out = idx + 0.05 ! the 0.05 is to adjust the idx to output the time 
> > between grounded and floating
> >
> > Now we can work around this by setting mode INTERP, saving the timeseries 
> > for each site, CAN DATA/ALL, can var/all, opening the saved timeseries and 
> > then doing the above masking operation. But for our large datasets, this
> > becomes awkward/slow. Anyway around this?
> >
> > To be concrete, with the above work around for one data site and model, I 
> > get out= -31.75
> > without the work around I get out=-119.9 with CAN MODE INTERP and -70.57 
> > with SET MODE INTERP
> >
> > Cheers,
> >
> > Lev
> >
> > Lev Tarasov -   Dept of Physics and Physical Oceanography,
> >         Memorial University of Newfoundland.
> >                 email: lev@xxxxxx
> >                 http://www.physics.mun.ca/~lev/
> >         Sabbatical Tel (519)-821-3555
> >         Fax (709)-864-8739
> >
> > This electronic communication is governed by the terms and conditions at
> > http://www.mun.ca/cc/policies/electronic_communications_disclaimer_2012.php 

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