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Issued by: Ole Einar Tveito (MET Norway) and Cristian Lussana (MET Norway)

Issued Date: 3130/0309/2024

Ref: M311_Lot3.3.1.2_NGCD_PUG_ver5ver7

Official reference number service contract:  C3S2 311 Lot3

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List of datasets covered by this document

Related documents

Acronyms 

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The NGCD undergoes full updates biannually, specifically in March and September. Following each update, a new version is released, labeled as Year.Month (for instance, the March September 2024 update is designated as ver. 24.0309). Semi-annual datasets released through the CDS will be publicly accessible for up to three years post-release. The latest version of this document pertains to NGCD ver. 24.0309.

Every version consists of two distinct archives: i) the historical archive and ii) the provisional archive (provisional data for a particular version are deleted when superseded by a subsequent historical archive).

For ver. 24.0309:

• The historical archive encompasses the period from January 1961 to December 2023June 2024. Any post-production modifications to the historical archive are documented in the "List of Known issues" and/or within the "Known Issues" section on the NGCD page on the MET Norway thredds server.

• The provisional archive is exclusive to NGCD-2 files. It starts from 1st January July 2024 and is updated daily. This means that some files, typically the most recent ones, can vary daily without specific notice. The methodologies employed for the provisional products mirror those used for the NGCD-2 historical archive. However, the observation data used as input is sourced from the open data application programming interfaces of of FMI, MET Norway, and SMHI. The provisional data from January July to June December 2024 will be superseded by the historical archive in the subsequent NGCD version.

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. 24.0309. Lastly, Appendix B showcases examples of file structures.

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The time series illustrating the number of stations used to produce NGCD version 24.03 09 are depicted in Figures 1-4, corresponding to RR, TG, TN and TX respectively. The number of RR stations in the region has decreased from approximately 2400 stations-per-day in 1980 to 1400 1550 stations-per-day in 2020, marking a decline of about 42%35%. This number has further decreased by 20232024. Conversely, for TG, the number of stations has been on the rise after 2010, growing from 800 stations-per-day in 2000 to slightly over 1300 stations-per-day in 2020, an increase of roughly 62%. This surge is primarily attributed to the integration of sub-regional networks in Norway, overseen by Norwegian public institutions. It's worth noting that the number of stations used for TG production after 2010 exhibits greater daily fluctuations compared to previous years. As for TX and TN, there's a steady decline in station numbers from 1971 to 1994. However, there's a resurgence and gradual increase from 1995 onwards. Between 1971 and 2020, the relative changes for TX and TN are less pronounced than for TG, with station numbers ranging from a low of about 700 to a high of 1000 1100 stations-per-day, reflecting an increase of around 43%57%.

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Figure 1: Daily precipitation total (RR): monthly time series of the number of stations used in the production of NGCD ver 24.03 09 from January 1961 to December 2023June 2024. For each month, the number of stations shown is the median of the stations available daily.

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Figure 2: Daily mean temperature (TG): monthly time series of the number of stations used in the production of NGCD ver 24.03 09 from January 1961 to December 2023June 2024. For each month, the number of stations shown is the median of the stations available daily.

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Figure 3: Daily minimum temperature (TN): monthly time series of the number of stations used in the production of NGCD ver 24.03 09 from January 1961 to December 2023June 2024. For each month, the number of stations shown is the median of the stations available daily.

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Figure 4: Daily maximum temperature (TX): monthly time series of the number of stations used in the production of NGCD ver 24.03 09 from January 1961 to December 2023June 2024. For each month, the number of stations shown is the median of the stations available daily.

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Regarding TN (and by implication, TX), the pattern echoes that of TG. However, a key distinction arises: until 2021, the observational network over Norway is relatively sparse. From 2021 onwards, a consistent observational network emerges for all temperature-related variables.

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Figure 5: Daily precipitation total (RR): 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 1). The left column shows maps over the domain while the right column shows the elevations of the stations (blue 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

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Figure 6: Daily mean temperature (TG): 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 2). The left column shows maps over the domain while the right column shows the elevations of the stations (red 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.

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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.

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• <Var> is one of: RR, TG, TX and TN
• <Id_type> is either 1 or 2
• <ver> is the version label in the format Year.Month (e.g. 24.0309)
• <Date> is in the form YYYYMMDD

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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.

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Figure 8 displays the RR fields for 10 January 2021. NGCD-1, which utilizes triangulation, incorporates local adjustments for precipitation in mountainous areas based on elevation. In contrast, NGCD-2 offers a more seamless precipitation field compared to NGCD-1, as it doesn't make elevation adjustments, leading to generally smoother RR fields. Regardless of type, in regions sparse with data, values echo broader-scale precipitation. In contrast, data-rich regions typically showcase a higher variability in the reconstructed field.

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Figure 8: Daily precipitation totals (RR, mm) for 10 January 2021: NGCD-1 on the left; NGCD-2 on the right.

Figures 9 and 10 respectively depict the TG and TN, TX for a day in spring, specifically 30 May 2021.

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Figure 9: Daily mean temperature (TG, ^oC) for 30 May 2021: NGCD-1 on the left; NGCD-2 on the right.

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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.

Cite NGCD as indicated on the link to "Citation" under References on the Overview page of NGCD.

MET Norway data

The Norwegian data is freely available from MET Norway via frost.met.no.

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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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