RELEASE NOTES FOR CRU TS v3.23: 25 June 2015 (rev. 23 October 2015) The 3.23 release of the CRU TS dataset covers the period 1901-2014. It supercedes all earlier releases. The reference to use is: Harris, I., Jones, P.D., Osborn, T.J. and Lister, D.H. (2014), Updated high-resolution grids of monthly climatic observations – the CRU TS3.10 Dataset. Int. J. Climatol., 34: 623–642. doi: 10.1002/joc.3711 Differences Between CRU TS v3.21 and v3.23, Known Issues, and the forthcoming 4.00 release. In addition to updating the dataset with 2014 data, some new stations have been added for TMP and PRE only. Known issues predating this release remain; the 4.00 release due Summer 2015 will address these. The 4.00 release will utilise Angular-Distance Weighting (ADW) gridding, promising more accurate results with far greater adjustability and logging. It will cover the same spatial, temporal and variate spaces as version 3.23 (land areas excluding Antarctica at 0.5°x0.5°, monthly from 1901 to 2014 with no missing values, 10 variables). Versions 3.23 and 4.00 will run concurrently until 2016, after which the new (ADW) approach will be used. This is to allow comparisons between the methods and results to be made by users of the dataset. 1. Known Issue: Interpolation near the International Date Line Affects: Eastern Siberia, all variables. In April 2014, a user notified BADC that they had discovered a discontinuity in data fields near to the International Date Line (ie, Eastern Siberia). This manifests as a vertical (ie, along a line of longitude) discontinuity approximately 2.5° (five gridcells) to the West of the Date Line (so, at about 177.5°E). Investigation of this phenomenon concluded that it was due to the gridding approach used: this is explained in the documentation, and consists of triangulation, followed by interpolation to the chosen grid points. The triangulation is not 'spherical', and so triangles do not form across the Date Line, this is causing the anomalous data. Despite exhaustive testing of available routines within the package that is being used, none have been found to deliver fields that are free from unwanted artifacts. This has been a significant driver in the imminent move to ADW gridding. 2. Known Issue: Anomalous Canadian data. Affects: Canada (esp. Eastern Canada), temperature variables. In May 2014, a user contacted CRU with statistical work showing a cold bias in CRU TS mean temperature data (TMP) over Eastern Canada, when compared to other datasets and models. This bias apears to begin in 2005 and runs until the present. Resources have not been available to investigate thoroughly. 3. WET (Rain Days) Faults were discovered in production of synthetic WET, and the variable was withdrawn - the bug has been corrected and a revised version of the WET dataset (v3.23.01) is now available and to be used. 4. Known Issue: Anomalous Indian PRE data. Erroneous values were found in the observational record for Cherrapunji station in India (). Correct values have been located in the World Weather Records (WWR) archives: Original WWR 1980 01 12 12 1980 02 684 684 1980 03 212 212 1980 04 740 740 1980 05 0 10414 1980 06 184 14723 1980 07 474 20756 1980 08 492 20796 1980 09 0 5876 1980 10 40 40 1980 11 0 0 1980 12 0 0 These will be included in future releases. 5. Known Issues: General differences from previous release. Affects: All variables, all releases At first glance, an update process should not change any existing published data unless it includes retrospective data for the previous time period. However, these are several ways in which new updates may affect published data from any time: a) New data for a station will change the standard deviation of that station. This is used to assess each observation of that station and to eliminate excessive values. So in 'borderline' cases, new data may block a previously-allowed datum, or alternatively may allow through a previously-blocked value. b) New metadata for any station can result in a relocation. This may simply be a correction, or improved accuracy: but any move will alter the triangulation process, and this can propogate over a wide area as the triangles are not constructed independently of each other. So a station move of perhaps 0.05 degrees could change an interpolated value many degrees away (and all of the others in between). This change will also apply to the whole station series, changing all triangles at every time step. This has been another significant driver in the imminent move to ADW gridding. As always, please contact BADC in the first instance if you have any questions, observations or suggestions. Ian Harris Climatic Research Unit School of Environmental Sciences University of East Anglia Norwich NR4 7TJ