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SciTools / iris-grib

GRIB interface for Iris.
https://iris-grib.readthedocs.io/
BSD 3-Clause "New" or "Revised" License
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Saving Iris Cubes containing GRIB-2 data is changing 'Fixed Surface' settings to inconsistent values. #338

Open mgange659 opened 1 year ago

mgange659 commented 1 year ago

Octets 23-34 in Section 4 of GRIB-2 messages store settings relating to the vertical coordinates describing the GRIB-2 data.

For GRIB-2 files loaded into a cube, iris.save makes these alterations before saving in a new file

Type of first fixed surface=6 (Maximum Wind Level) changed to Type of first fixed surface=1 (Ground) Type of first fixed surface=7 (Tropopause) changed to Type of first fixed surface=1 (Ground)

and for all screen-level parameters at 1.5 metres:- Scale Factor of first fixed surface=1 (101) changed to Scale Factor of first fixed surface=0 (100) Scaled Value of first fixed surface=15 (1.5m) changed to Scaled Value of first fixed surface=2 (2m)

trexfeathers commented 1 year ago

@SciTools/peloton: this is a known limitation due to our minimal implementation; good to have it recorded officially.

It is unclear when we will have resource to address this. Any information on priority / other context would be helpful for decision making (remembering that this a public repo!). Thanks 🙂

mgange659 commented 1 year ago

This issue is currently LOW priority. I am exploring possible options for creating re-gridded GRIB products from full sized MDDA GRIB-2 files so that older code can be decommissioned.

pp-mo commented 7 months ago

I think we can't expect iris-grib to preserve the scaling, but ideally it would always selectt a sensible one. I think that links this to #205