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History of modifications

List of datasets covered by this document

Related documents

Acronyms 

Main variables

Data access information

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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 primary objective of this guide is to assist users in comprehending both the features and potential limitations of the dataset. Furthermore, it aims to provide clear instructions on how to access, read, and effectively utilize the data.

Executive summary

The NGCD is an observational gridded dataset that covers Fennoscandia, encompassing Finland, Norway, and Sweden. It exclusively relies on in-situ observations. The dataset includes the following main variables: daily mean temperature (TG); daily maximum temperature (TX); daily minimum temperature (TN); daily total precipitation (RR).

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For data access, please refer to the provided links in the "Data access information" section. A comprehensive description of NGCD is presented in the "Product information" section. Additionally, Appendix A details the evaluation for ver. 18.03, which is consistent with the methodologies employed for all versions up to ver. 25.03. Lastly, Appendix B showcases examples of 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 D1, 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 D2 in Section Related Documents.

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ii) While there's a mention of a version, signaling the methodology deployed in data production, the source of these observations diverges from the historical archive of the corresponding version.

Data format

The key fields provided in this product are as given in Table 1.

The provided data is single-layered, situated near the surface, and gridded on a regular grid covering Finland, Norway, and Sweden. Excluding a narrow buffer that extends a few kilometers into the sea, the grid is masked in regions beyond this domain and over the ocean due to the absence of in-situ observations. Utilizing the Lambert Azimuthal Equal Area projection as its coordinate reference system, the grid spacing is of 1 km in both the Easting and Northing directions. Specifically, its dimensions span 1550 units in Easting and 2020 in Northing. Figures 5-7 graphically represent this spatial domain.

On accessing files from the CDS, users receive individual files tailored to each specific day, variable, and requested NGCD-type. Notably, these fields carry a time dimension, which consistently measures a length of one.

Product content examples

Figures 8-10 provide illustrations of NGCD products for two distinct days.

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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 Temperature and Precipitation are based on NGCD version 18.03 and the data used covers the 46-year period from 1971 to 2016.

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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.

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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