11 January 2022: Advance Warning: revised climatologies
In September 2021 we were contacted by Bruno Lemke (NMIT, NZ). Together
with his colleagues Matthias Otto (NMIT) and Tord Kjellstrom (HEIT, NZ),
he had identified anomalies in the CRU CL v1.0 0.5° climatologies.
These fields underly CRU TS, as they are used to convert gridded
anomalies back into actuals for publication.
Upon investigation, we found a number of 'unrealistic' areas. There
was no obvious pattern to these areas, occurring in different parts
of the world and on different months, for several variables. A
forthcoming technical note will detail this work in full.
We elected to regenerate the half-degree climatologies from the
ten-minute climatologies (CRU CL v2) published a few years later,
arriving at new half-degree climatologies that eliminate the issues
found. This will affect all CRU TS variables to a greater or lesser
extent. It will not alter changes over time, such as trends, because
the climatology is applied equally to every January, every Febrary,
and so on.
The next version of CRU TS will be v4.06; it was not felt necessary
to increment the primary version number for what is essentially a
'bug fix'. However, in some parts of the world there will be
noticeable differences from v4.05; as usual, comparison plots will
be available.
We thank Bruno Lemke and colleagues for their diligence in locating
these anomalies.
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