RELEASE NOTES FOR CRU TS v4.06: 26 May 2022

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 4.06 release of the CRU TS dataset covers the period 1901-2021.

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


1. What's new in 4.06

1.1 Process changes

The underlying climatology, CRU CL v1, which is used to convert gridded
anomalies into actuals for publication, has been updated. This will be
documented in a forthcoming Technical Note, but in essence it was
necessary to recalculate the climatologies - and this was done by
regridding the higher-resolution CRU CL v2. The results of this change
are widespread, though only significant in certain places, and are
consistent (for a given month) over the whole time period. Hence, no
trends have been affected.

The process by which CLD observations are synthesised from primary
variables has been overhauled. New regressions were established between
CLD and DTR in 5°x5° bins. These were then interpolated onto the 0.5°
CRU TS grid. The resulting gridded coefficients were then applied to the
gridded DTR anomalies arising from earlier DTR production in the main
process, yielding grids of synthetic CLD anomalies. These are then fed
into the main gridding process for CLD, alongside the CLD observations
(and with the usual rules about observations taking precedence, etc).
This approach follows more closely the approach taken in the earliest
versions of CRU TS:

New, M., Hulme, M. & Jones, P. D. Representing twentieth-century space–
time climate variability. Part II: development of 1901–96 monthly grids
of terrestrial surface climate. J. Climate 13, 2217–2238,
https://doi.org/10.1175/1520-0442(2000)013<2217:RTCSTC>2.0.CO;2 (2000).

1.2 Bug fixes

Only to the climatology (see above).

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. 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