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List of datasets covered by this document
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Related documents
| Reference ID | Document | ||||||
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D1
| NGCD Algorithm Theoretical Basis Document | ||||||
D2
| Climate and Forecast (CF) Conventions and Metadata; http://cfconventions.org | ||||||
D3
| R Core Team (2017). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/ |
Acronyms
Acronym | Definition |
CDS | |
MET Norway | |
FMI | |
KNMI | |
SMHI | |
NGCD | Nordic Gridded Climate Dataset (DOI:https://doi.org/10.24381/cds.e8f4a10c |
NGCD-1 | NGCD type 1 datasets |
NGCD-2 | NGCD type 2 datasets |
seNorge | Observational gridded dataset over Norway (senorge.no) |
ECA&D | |
TITAN | |
OI | Optimal Interpolation |
| RMSE | Root Mean Squared Error |
General definitions
Symbol | Definition |
TG | Daily mean temperature (from day before the date in the timestamp at 06 UTC, to date in the timestamp at 06 UTC) |
TX | Daily maximum temperature (from day before the date in the timestamp at 18 UTC, to date in the timestamp at 18 UTC) |
TN | Daily minimum temperature (from day before the date in the timestamp at 18 UTC, to date in the timestamp at 18 UTC) |
RR | Daily precipitation total (from day before the date in the timestamp at 06 UTC, to date in the timestamp at 06 UTC) |
Data access information
Anchor table_data_access table_data_access
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The list of Known issues is available at the following link.
Scope of the document
This document is the user guide for the NGCD observational gridded dataset produced under the service contract C3S2_311 Lot3 (Collection and processing of in situ observations - Access to high-resolution gridded datasets over Europe based on in situ observations) on behalf of Copernicus.
The main aim of this document is to aid the user in understanding the features and limitations of the data, and then to enable them to read and use the data.
Executive summary
NGCD is an observational gridded dataset covering Fennoscandia (Finland, Norway and Sweden) based on in-situ observations only. The variables included in the dataset are (see General definitions): daily mean temperature, TG; daily maximum temperature, TX; daily minimum temperature, TN; and daily total precipitation, RR.
NGCD consists of two independent datasets, NGCD-1 and NGCD-2, derived using different spatial interpolation methods applied to the same input observation dataset. The description of the input data and the methods is available in the NGCD Algorithm Theoretical Basis Document (Nordic Gridded Climate Dataset (NGCD): Product User Guide and Specification (PUGS)). NGCD programs are written using R-language Nordic Gridded Climate Dataset (NGCD): Product User Guide and Specification (PUGS). The NGCD algorithms and scripts are available at github.com/metno/NGCD.
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The data can be found at the links specified in the Data access information. The main description of NGCD is in the Product information section. Then, Appendix A reports the evaluation made for ver. 18.03, which shares the same methods used for ver. 22.03. Appendix B contains examples of the file structures.
Product information
Product description
The description of the input data and the methods is available in the NGCD Algorithm Theoretical Basis Document [D1]. As specified in Nordic Gridded Climate Dataset (NGCD): Product User Guide and Specification (PUGS), the user must be aware that the NGCD input data are non-homogenized time series.
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Figure 7: Daily minimum temperature (TN): spatial distribution of the observing stations used in the production of NGCD when the observational network consists of a smaller number of stations (“sparse” observational network, top row) and a larger number of stations (“dense” observational network, bottom row) with respect to the the time series of available observations (see Figure 3). The left column shows maps over the domain while the right column shows the elevations of the stations (green dots) as a function of their Northing coordinates. As a reference in the background, the gray dots are the elevations of the cells on the 1 km digital elevation model over Fennoscandia.
Data usage information
File naming convention
The data files are in netCDF-4 format and follow the CF-standards, see Nordic Gridded Climate Dataset (NGCD): Product User Guide and Specification (PUGS) in Section Related Documents.
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where the meaning of the variable parts inside the symbols <...> is the same as for the historical archive. It is worth remarking that: i) the provisional files are made for NGCD-2 only; ii) there is reference to a version, which indicates the methodology used in the data production, though the source of the observations is different to that in the historical archive of the same version.
Data format
The key fields provided in this product are as given in Table 1.
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When downloading files from the CDS, users obtain one file for each: day, variable and NGCD-type requested. The fields also have a time dimension, which always has a length of one.
Product content examples
Examples of NGCD products on two generic days are shown in Figures 8-10.
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Figure 10: Daily minimum and maximum temperatures (TN top row, TX bottom row, oC) for 30 May 2021: NGCD-1 in the left column; NGCD-2 in the right column.
Data usage acknowledgments
All users of NGCD must provide clear and visible attribution to the Copernicus programme and are asked to cite and reference the dataset provider. Acknowledge according to the licence to use Copernicus Products.
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We acknowledge the data providers in the ECA&D project. Klein Tank, A.M.G. and Coauthors, 2002. Daily dataset of 20th-century surface air temperature and precipitation series for the European Climate Assessment. Int. J. of Climatol., 22, 1441-1453. Data and metadata available at https://www.ecad.eu
Appendix A - Evaluation of version 18.03
The evaluations presented in this Appendix for Nordic Gridded Climate Dataset (NGCD): Product User Guide and Specification (PUGS) and Nordic Gridded Climate Dataset (NGCD): Product User Guide and Specification (PUGS) are based on NGCD version 18.03 and the data used covers the 46-year period from 1971 to 2016.
Temperature
The strategy used for evaluation is cross-validation by means of a leave-one-out procedure. In this way, NGCD is evaluated against independent observations, which are used as reference values. NGCD values are interpolated to the observation locations using a bilinear interpolation. The score considered in the evaluation is the root mean square error (RMSE) based on the deviations between estimated and reference values.
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Figure A9: Daily mean temperature (TG): RMSE (oC), same as Figure A8 but for August.
Precipitation
For precipitation the cross-validation study is carried out on a selection of 50 stations (Figure A10), which have not been used in the production of NGCD. This cross-validation approach differs from the one used for temperature because all 50 stations are reserved for evaluation simultaneously and not one at a time, as in leave-one-out cross-validation. The estimates are compared with the independent observations by means of standard verification scores like probability of detection (POD), false alarm rate (FAR, also known as probability of false detection or POFD), equitable threat score (ETS) and bias score. We refer to the page of the 7th International Verification Methods Workshop for the score definitions.
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Figure A14: Bias score (dimensionless) of daily precipitation totals (RR) for events exceeding given thresholds (0.1,0.5,1,5,10 and 25 mm) for NGCD-1 (black boxes) and NGCD-2 (red boxes).
Appendix B - Example file structure
Example file structure can be seen directly from the web-browser at the following URLs.
Var | URL with example of file structure |
RR | |
TG | |
TX | |
TN |
References
Klein Tank, A. M., Wijngaard, J. B., Können, G. P., Böhm, R. , Demarée, G. , Gocheva, A. , Mileta, M., Pashiardis, S. , Hejkrlik, L. , Kern‐Hansen, C. , Heino, R. , Bessemoulin, P. , Müller‐Westermeier, G. , Tzanakou, M. , Szalai, S. , Pálsdóttir, T. , Fitzgerald, D. , Rubin, S. , Capaldo, M. , Maugeri, M. , Leitass, A. , Bukantis, A. , Aberfeld, R. , van Engelen, A. F., Forland, E. , Mietus, M. , Coelho, F. , Mares, C. , Razuvaev, V. , Nieplova, E. , Cegnar, T. , Antonio López, J. , Dahlström, B. , Moberg, A. , Kirchhofer, W. , Ceylan, A. , Pachaliuk, O. , Alexander, L. V. and Petrovic, P. (2002), Daily dataset of 20th‐century surface air temperature and precipitation series for the European Climate Assessment. Int. J. Climatol., 22: 1441-1453. doi:10.1002/joc.773
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This document has been produced in the context of the Copernicus Climate Change Service (C3S). The activities leading to these results have been contracted by the European Centre for Medium-Range Weather Forecasts, operator of C3S on behalf of the European Union (Delegation agreement signed on 11/11/2014). All information in this document is provided "as is" and no guarantee or warranty is given that the information is fit for any particular purpose. The users thereof use the information at their sole risk and liability. For the avoidance of all doubt , the European Commission and the European Centre for Medium - Range Weather Forecasts have no liability in respect of this document, which is merely representing the author's view. |
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