[ferret_users] Time regridding from descriptor file returns missing values

Hi,

I discovered an odd inconsistency when time regridding with Ferret that is most likely a bug, or at least an annoying feature, assuming I am not doing something wrong. Attached is a script and data files necessary to reproduce the issue. If I read a variable directly from a netcdf file, assign a time axis to it, and then regrid to a second time axis I get the desired result. In my case, the data in the netcdf file is every 3 hours and I would like to regrid to daily data. So far so good. Next, I wrap the netcdf file with a descriptor file to take care of mapping the 3-hourly time axis for the data in the netcdf file. Then, I do the same time regridding to the daily time axis. This time the result is missing values instead of daily data.

For the attached simplified case, there is the trivial fix of not using the des file. However, in production situations, this complicates things a lot for me. Is this "missing value" feature a bug? Am I doing something wrong? I have been able to reproduce the problem in both Ferret v6.9.3 and v7.1 on a Linux box.

Thanks for any suggestions.

-Bill

The script that produces the error:

---SCRIPT BEGIN---

! Script demonstrating a Ferret bug/feature when doing time interpolation

! from input directly from a netCDF file vs. input that has been read via

! a descriptor file. For some reason, when regridding data read via the

! descriptor file results in all missing values. However, bypassing the

! des file and assigning the time grid from the Ferret command line

! before doing the regridding works.

! William.Gustafson@xxxxxxxx, 18-Apr-2017

use timeseries.nc

use timeseries.des

! Define needed time axes

define axis/t/t0="1-jan-2011:00"/t="1-jan-2011:00":"1-may-2011:00":3/units=hour tax3h

define axis/t/t0="1-jan-2011:00"/t="1-jan-2011:00":"1-may-2011:00":1/edges/units=day taxday

! Set up daily data from 3-hourly data via nc file. First, map the data

! to the 3-h grid, and then regrid to the final daily grid. This works.

let nc3h = t2[gt=tax3h@asn,d=1]

let nc1day = nc3h[gt=taxday]

! Set up daily data from 3-hourly data via des file. The descriptor file

! is responsible for putting the data on the 3-h grid this time. Then,

! we regrid to the daily grid. This returns missing values.

let des3h = t2[d=2] !des file defines this as 3-hourly

let des1day = des3h[gt=taxday]

list nc1day, des1day

---SCRIPT END---

---TRUNCATED OUTPUT FROM SCRIPT BEGIN---

TIME: 01-JAN-2011 00:00 to 01-MAY-2011 00:00

X: 100

Y: 100

Column 1: NC1DAY is NC3H[GT=TAXDAY]

Column 2: DES1DAY is DES3H[GT=TAXDAY]

NC1DAY DES1DAY

01-JAN-2011 12 / 1: 250.5 ....

02-JAN-2011 12 / 2: 256.0 ....

03-JAN-2011 12 / 3: 253.7 ....

04-JAN-2011 12 / 4: 250.0 ....

05-JAN-2011 12 / 5: 241.8 ....

06-JAN-2011 12 / 6: 237.3 ....

07-JAN-2011 12 / 7: 251.9 ....

08-JAN-2011 12 / 8: 247.3 ....

09-JAN-2011 12 / 9: 247.0 ....

---TRUNCATED OUTPUT FROM SCRIPT END---

___________________________________________________________________

William I. Gustafson Jr., Ph.D.

Scientist 

ATMOSPHERIC SCIENCES AND GLOBAL CHANGE DIVISION

 Pacific Northwest National Laboratory

P.O. 999, MSIN K9-30

Richland,WA 99352

Tel: 509-372-6110

William.Gustafson@xxxxxxxx

http://www.pnnl.gov/atmospheric/staff/staff_info.asp?staff_num=5716

http://www.researcherid.com/rid/A-7732-2008