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v2.3 (19 Dec 2019)#

This document explains the changes made to Iris for this release (View all changes.)

Features#

Support for CF 1.7

We have introduced several changes that contribute to Iris’s support for the CF Conventions, including some CF 1.7 additions. We are now able to support:

You can read more about each of these below.

Additionally, the conventions attribute, added by Iris when saving to NetCDF, has been updated to CF-1.7, accordingly.

Climatological Coordinate Support

Iris can now load, store and save NetCDF climatological coordinates. Any cube time coordinate can be marked as a climatological time axis using the boolean property: climatological. The climatological bounds are stored in the coordinate’s bounds property.

When an Iris climatological coordinate is saved in NetCDF, the NetCDF coordinate variable will be given a ‘climatology’ attribute, and the contents of the coordinate’s bounds property are written to a NetCDF boundary variable called ‘<coordinate-name>_bounds’. These are in place of a standard ‘bounds’ attribute and accompanying boundary variable. See below for an example adapted from CF conventions:

dimensions:
  time=4;
  bnds=2;
variables:
  float temperature(time,lat,lon);
    temperature:long_name="surface air temperature";
    temperature:cell_methods="time: minimum within years time: mean over years";
    temperature:units="K";
  double time(time);
    time:climatology="time_climatology";
    time:units="days since 1960-1-1";
  double time_climatology(time,bnds);
data:  // time coordinates translated to date/time format
  time="1960-4-16", "1960-7-16", "1960-10-16", "1961-1-16" ;
  time_climatology="1960-3-1",  "1990-6-1",
                   "1960-6-1",  "1990-9-1",
                   "1960-9-1",  "1990-12-1",
                   "1960-12-1", "1991-3-1" ;

If a climatological time axis is detected when loading NetCDF - indicated by the format described above - the climatological property of the Iris coordinate will be set to True.

New Chunking Strategy

Iris now makes better choices of Dask chunk sizes when loading from NetCDF files: If a file variable has small, specified chunks, Iris will now choose Dask chunks which are a multiple of these up to a default target size.

This is particularly relevant to files with an unlimited dimension, which previously could produce a large number of small chunks. This had an adverse effect on performance.

In addition, Iris now takes its default chunk size from the default configured in Dask itself, i.e. dask.config.get('array.chunk-size').

Lazy Statistics

Several statistical operations can now be done lazily, taking advantage of the performance improvements offered by Dask:

Bugs Fixed#

  • Cube equality of boolean data is now handled correctly.

  • Fixed a bug where cell measures were incorrect after a cube transpose() operation. Previously, this resulted in cell-measures that were no longer correctly mapped to the cube dimensions.

  • The AuxCoord disregarded masked points and bounds, as did the DimCoord. Fix permits an AuxCoord to contain masked points/bounds, and a TypeError exception is now raised when attempting to create or set the points/bounds of a DimCoord with arrays with missing points.

  • iris.coord_systems.VerticalPerspective coordinate system now uses the CF Vertical perspective definition; had been erroneously using Geostationary.

  • CellMethod will now only use valid NetCDF name tokens to reference the coordinates involved in the statistical operation.

  • The following var_name properties will now only allow valid NetCDF name tokens to reference the said NetCDF variable name. Note that names with a leading underscore are not permitted.

  • Rendering a cube in Jupyter will no longer crash for a cube with attributes containing \n.

  • NetCDF variables which reference themselves in their cell_measures attribute can now be read.

  • quiver() now handles circular coordinates.

  • The names of cubes loaded from abf/abl files have been corrected.

  • Fixed a bug in UM file loading, where any landsea-mask-compressed fields (i.e. with LBPACK=x2x) would cause an error later, when realising the data.

  • iris.cube.Cube.collapsed() now handles partial collapsing of multidimensional coordinates that have bounds.

  • Fixed a bug in the PROPORTION aggregator, where cube data in the form of a masked array with array.mask=False would cause an error, but possibly only later when the values are actually realised. ( Note: since netCDF4 version 1.4.0, this is now a common form for data loaded from netCDF files ).

  • Fixed a bug where plotting a cube with a iris.coord_systems.LambertConformal coordinate system would result in an error. This would happen if the coordinate system was defined with one standard parallel, rather than two. In these cases, a call to as_cartopy_crs() would fail.

  • iris.cube.Cube.aggregated_by() now gives correct values in points and bounds when handling multidimensional coordinates.

  • Fixed a bug in the iris.cube.Cube.collapsed() operation, which caused the unexpected realization of any attached auxiliary coordinates that were bounded. It now correctly produces a lazy result and does not realise the original attached AuxCoords.

Internal#

  • Iris now supports Proj4 up to version 5, but not yet 6 or beyond, pending fixes to some cartopy tests.

  • Iris now requires Dask >= 1.2 to allow for improved coordinate equality checks.

Documentation#

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