RELEASE NOTES FOR CRU TS v4.08: 27 June 2024

The CRU TS dataset was developed and has been subsequently updated,
improved and maintained with support from a number of funders,
principally the UK's Natural Environment Research Council (NERC) and the
US Department of Energy. Long-term support is currently provided by the
UK National Centre for Atmospheric Science (NCAS), a NERC collaborative
centre. 

The 4.08 release of the CRU TS dataset covers the period 1901-2023.

The new interpolation algorithm is unchanged since v4.03.

To understand this dataset, it is important to understand its
construction and limitations. It is therefore recommended that all users
read the relevant paper:

Harris, I., Osborn, T.J., Jones, P. et al. Version 4 of the CRU TS
monthly high-resolution gridded multivariate climate dataset.
Sci Data 7, 109 (2020). https://doi.org/10.1038/s41597-020-0453-3

0. IMPORTANT

After a partial release on 24 June, inconsistencies were found in the
DTR product, and those secondary and tertiary variables that use DTR.
The problem was traced to a minor change in code earlier this year,
which turned out to be a major change! The whole version has been
recalculated in two runs:

#2406270035:  TMP, PRE, DTR, VAP, WET
#2406270856:  CLD, FRS, PET, TMN, TMX

Internal consistency between variables has been maintained.

1. What's new in 4.08

1.1 Process changes

For TMP and PRE, the selection process for interpolant stations
('cohorts') for each gridcell has been enhanced, in that cohorts that
appear broadly similar interms of behaviour will be used instead of
the closest eight or fewer (which is what the process was). For TMP
and PRE, this has reduced some periodic excessive variablility, and
will be fine-tuned in future releases. It is planned that this
enhancement will be extended to DTR in the next release.

As part of this change, new quality variables have been produced (and
are included in the NetCDF versions) for most variables. They are:

MAE: Mean Absolute Error. The mean of the absolute differences between
     interpolant anomalies and the resultant gridded value.
MAEA: MAE Anomaly, relative to the long-term mean.

As before, there is also 'stn', giving a count of the number of
interpolant stations for each gridded value.

2. Output files

For now, the approach of issuing NetCDF and ASCII files in parallel will
remain, as will the publications of decadal files as well as full-length
versions. However, decadal files may not be archived when superceded, in
order to make best use of space.

As always, please contact BADC in the first instance if you have any
questions, observations or suggestions (and have acquired CRU TS from
them). If, however, you wish to contact CRU directly about these datasets,
please contact me at i.harris@uea.ac.uk, as mail to other members of the
Unit will be passed through to me anyway.

Ian Harris
NCAS-Climate
Climatic Research Unit
School of Environmental Sciences
University of East Anglia
Norwich
NR4 7TJ

i.harris@uea.ac.uk