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



Hi Ansley;
	I just tried it, and no difference: Ie
LET mask_grounded = if H*rhoI/rhoO gt Hw then 1
doesn't change the results and
the combo
LET mask_grounded1 = if H*rhoI/rhoO gt Hw then 1
LET mask_grounded = if mask_grounded1 then 1 else 0
gives the same (max=0.46) stats

The problem I guess is that the interpolation is acting
on the result of the IF THEN masking, instead of having
the masking act on interpolated values. Anyway around this (aside
from the awkward file write/read)?

l

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, Ansley Manke wrote:

Lev
Would the logic in your script still work as intended if you define the mask without the ELSE 0,

  if  expression then 1

so that the else is missing rather than 0?  Then define a second mask,

  let newmask = if mask_grounded then 1 else 0

and I think you could use @EVNT with that.


On 8/8/2013 4:46 AM, Lev Tarasov wrote:
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

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