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Issued by: Ole Einar Tveito (MET Norway) and Cristian Lussana (MET Norway)
Issued Date: 3130/0309/2023
Ref: M311_Lot3.3.1.2_NGCD_PUG_ver4ver5
Official reference number service contract: C3S2 311 Lot3
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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 |
Main variables
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
Description | Link |
---|---|
The historical archive for different versions is made available to users via the CDS | https://cds.climate.copernicus.eu/cdsapp#!/dataset/insitu-gridded-observations-nordic |
The data are also available to users via MET Norway OPeNDAP access | https://thredds.met.no/thredds/catalog/ngcd/catalog.html |
MET Norway. Historical archive ver. 23. |
09 (for different versions, replace 23. |
09 with the correct label) |
MET Norway. Provisional archive | https://thredds.met.no/thredds/catalog/ngcd/provisional/catalog.html |
The list of Known issues is available at the following link.
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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 primary objective of this document guide is to aid the user in understanding assist users in comprehending both the features and potential limitations of the data, and then to enable them to read and use 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 covering that covers Fennoscandia (, encompassing Finland, Norway, and Sweden) based . It exclusively relies on in-situ observations only. The variables included in the dataset are (see Main variables)dataset includes the following main variables: daily mean temperature , (TG); daily maximum temperature , (TX); daily minimum temperature , (TN); and daily total precipitation , (RR).
NGCD consists of comprises two independent datasets, : NGCD-1 and NGCD-2, derived using . Both are derived by employing different spatial interpolation methods applied to techniques on the same input observation observational dataset. The description of Comprehensive details about the input data and the methods is available methodologies can be found in the NGCD Algorithm Theoretical Basis Document (D1).. NGCD programs are written using R-language D3. The NGCD algorithms and scripts are available 's programs utilize the R programming language D3, and the algorithms and scripts can be accessed at github.com/metno/NGCD.
The data products are provided structured on a regular grid, using a defined by the Lambert Azimuthal Equal Area coordinate reference system, with a spacing of . The grid spacing is 1 km in both Easting and Northing directions. For each day, 8 eight fields are providedavailable: 4 with four from NGCD-1 methods (i.e. one for each variable) and 4 with four from NGCD-2 methods. Each field of these fields is stored in a separate distinct file, and all the data files are in adopt the netCDF-4 format.
NGCD is fully updated twice a year, The NGCD undergoes full updates biannually, specifically in March and September. Each Following each update yields , a new version is released, which is labelled labeled as Year.Month (e.g. the update in March 2023 yields for instance, the September 2023 update is designated as ver. 23.0309). The halfSemi-yearly updated annual datasets available released through the CDS will be made publicly available accessible for up to 3 three years after the post-release. This document has been updated The latest version of this document pertains to NGCD ver. 23.0309.
Each Every version is made up 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).
In the case of For ver. 23.0309:
The historical archive
coversencompasses the
timeperiod
that rangesfrom January
19711961 to June
2022. Any changes made in2023. Any post-production
onmodifications to the historical archive are
reported ondocumented in the "List of Known issues" and/or
inwithin the "Known
issuesIssues" section on the NGCD page on the MET Norway thredds server.
The provisional archive
includesis exclusive to NGCD-2 files
only. It
begins with files of the 1st of Januarystarts from 1st July 2023 and is
regularly updated every day, suchupdated daily. This means that some
of the files (i.e. usuallyfiles, typically the most recent ones
) may change from day to day, without any particular warnings. The products are obtained using the same methods as for the historical archive of NGCD-2, can vary daily without specific notice. The methodologies employed for the provisional products mirror those used for the NGCD-2 historical archive. However, the
observationsobservation data used as input
data are retrievedis sourced from the open data application programming interfaces of
:FMI, MET Norway, and SMHI.
The provisional archive for the period from January to JuneThe provisional data from July to December 2023 will be
replacedsuperseded by the historical archive
ofin the
nextsubsequent NGCD version.
The data can be found at the links specified in the For data access, please refer to the provided links in the "Data access information" section. The main A comprehensive description of NGCD is presented in the "Product information" section. ThenAdditionally, Appendix A reports details the evaluation made for ver. 18.03, which shares the same methods used is consistent with the methodologies employed for all versions up to to ver. 23.0309. Lastly, Appendix B contains showcases examples of the file structures.
Product information
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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.
The time series of illustrating the number of stations used for the production of NGCD ver to produce NGCD version 23.03 09 are shown depicted in Figures 1-4 for , corresponding to RR, TG, TN and TX , respectively. The number of RR stations in the region decreases, has decreased from around approximately 2400 stations-per-day in 1980 to 1400 stations-per-day in 2020 (≅ -42%). For TG, the situation is the opposite and , marking a decline of about 42%. This number has further decreased by 2023. Conversely, for TG, the number of stations grows has been on the rise after 2010, growing from 800 stations-per-day in 2000 to a bit more than slightly over 1300 stations-per-day in 2020 (≅ +62%). The main reason for the increase is the inclusion , an increase of roughly 62%. This surge is primarily attributed to the integration of sub-regional networks over in Norway, managed overseen by Norwegian public institutions. Note It's worth noting that the number of stations used in the for TG production of TG after 2010 has a larger day-to-day variability than before. exhibits greater daily fluctuations compared to previous years. As for TX and TN undergo a gradual decrease in the number of stations , there's a steady decline in station numbers from 1971 to 1994, which is followed by a turnaround with gradual growth . However, there's a resurgence and gradual increase from 1995 onwards. Between 1971 and 2020, the relative variations changes for TX and TN are more limited less pronounced than for TG, with the minimum number around 700 stations-per-day and the maximum station numbers ranging from a low of about 700 to a high of 1000 stations-per-day (≅ +43%). In 2021 and 2022, there are more stations available than in 2020, for all variables., reflecting an increase of around 43%.
Anchor figure1 figure1
Figure 1: Daily precipitation total (RR): monthly time series of the number of stations used in the production of NGCD ver 23.03 09 from January 1971 1961 to December 2022June 2023. For each month, the number of stations shown is the median of the stations available daily.
Anchor figure2 figure2
Figure 2: Daily mean temperature (TG): monthly time series of the number of stations used in the production of NGCD ver 23.03 09 from January 1971 1961 to December 2022June 2023. For each month, the number of stations shown is the median of the stations available daily.
Anchor figure3 figure3
Figure 3: Daily minimum temperature (TN): monthly time series of the number of stations used in the production of NGCD ver 23.03 09 from January 1971 1961 to December 2022June 2023. For each month, the number of stations shown is the median of the stations available daily.
Anchor figure4 figure4
Figure 4: Daily maximum temperature (TX): monthly time series of the number of stations used in the production of NGCD ver 23.03 09 from January 1971 1961 to December 2022June 2023. For each month, the number of stations shown is the median of the stations available daily.
The Figures 5-7 illustrate the spatial distribution of the observing observation stations over across the domain is shown in Figures 5-7 for for the variables RR, TG and , and TN , respectively. The Since the distribution pattern for TX is similar to that for TN and therefore is not shownclosely mirrors that of TN, it isn't separately depicted. For RR and TG, the two panels on in the top row show the situation when the present scenarios where the number of stations is close to near the minimum available within the period (“sparse” observational network), while period's minimum, indicative of a "sparse" observational network. Conversely, the two panels on the bottom row show the opposite situation, when the maximum number of stations is used. For TN, in Figure 7, the stations are shown for 2020 (“sparse”) and 2021 (“dense”). The panels in the left columns show the map with the distribution of stations over the domain. In the right columns, the panels are used to display the observational coverage as a function of elevation.depict situations with the maximum station count. In the case of TN, Figure 7 contrasts the distributions in 2020 ("sparse" network) and 2021 ("dense" network).
A closer examination of the figures reveals: left column panels provide maps showcasing station distributions throughout the domain; right column panels focus on observational coverage concerning elevation.
Upon assessing RR, a discernible decline in station count over time becomes evident. This decline notably affects the map's representation and, more strikingly, highlights elevation areas not sufficiently covered by the observational network. Specifically, in the northern regions, the network does not cover more than half of the higher elevation range.
In the context of TG, there's a concentration of the increase in station numbers over Norway, leading to a more consistent sampling across various elevations than seen with RR.
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 For RR, the number of stations decreases over the years and the impact is clearly visible both in the map and, especially, over the range of elevations not covered properly by the observational network. In the north, more than half of the elevation range (i.e. the higher elevations) is not covered by the network. In the case of TG, the increase in the number of stations is concentrated over Norway and the range of elevations is more uniformly sampled than for RR. For TN (and TX), the situation is similar to TG, except that until 2021 the observational network over Norway is less dense. From 2021, the observational network is similar for all temperature variables.
Anchor figure5 figure5
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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
Anchor figure6 figure6
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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The data files are in netCDF-4 format and follow the CF-standards, see D2 in Section Related Documents.
For the historical archive, the file names have the format:
NGCD_<Var>_type<Id_type>_version_<ver>_<Date>.nc
Where:
- <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. 23.0309)
- <Date> is in the form YYYYMMDD
...
NGCD_<Var>_type2_version_<ver>_prov_<Date>.nc
where Where the meaning of the variable parts inside components within the symbols <...> is the same as for mirrors that of 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 , it's noteworthy to highlight:
i) Only NGCD-2 is provided in the provisional archive.
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 same corresponding version.
Data format
The key fields provided in this product are as given in Table 1.
Table 1: Key data fields in the output files. Anchor table1 table1
Variable Name | Description |
lon | longitudes of the grid points |
lat | latitudes of the grid points |
projection_laea | specification of the coordinate reference system |
time_bounds | time bounds of the aggregated variable |
TG / TX / TN / RR | daily variable in the file |
The provided data are provided on a single layer, is single-layered, situated near the surface, and gridded on a regular grid covering Finland, Norway, and Sweden. The grid is masked outside the Excluding a narrow buffer that extends a few kilometers into the sea, the grid is masked in regions beyond this domain and over the sea, where no ocean due to the absence of in-situ observations are available, apart from a buffer extending over the sea for a few kilometers. The coordinate reference system is . Utilizing the Lambert Azimuthal Equal Area projection and as its coordinate reference system, the grid has a resolution spacing is of 1 km in both the Easting and Northing directions. The dimension of the data field is 1550 in the Specifically, its dimensions span 1550 units in Easting and 2020 in the Northing. The spatial domain is shown in Figures 5-7 graphically represent this spatial domain.
When downloading On accessing files from the CDS, users obtain one file for each: receive individual files tailored to each specific day, variable, and requested NGCD-type requested. The fields also have Notably, these fields carry a time dimension, which always has consistently measures a length of one.
Product content examples
Examples Figures 8-10 provide illustrations of NGCD products on for two generic days are shown in Figures 8-10.distinct days.
Figure 8 displays the The RR fields for 10 January 2021 are shown in Figure 8. NGCD-1 is based on triangulation and the precipitation is adjusted for local effects in mountainous regions, , which utilizes triangulation, incorporates local adjustments for precipitation in mountainous areas based on elevation. In contrast, NGCD-2 reconstructs offers a more continuous seamless precipitation field than compared to NGCD-1, without as it doesn't make elevation adjustments, so its leading to generally smoother RR fields look generally smoother. For both types, the values in data-sparse regions are representative of larger-scale precipitation than those in data-dense regions, where the reconstructed field variability is usually higher. 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.
Anchor figure8 figure8
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 show respectively depict the TG and TN, TX for a day in spring day, specifically 30 May 2021.
Anchor figure9 figure9
Figure 9: Daily mean temperature (TG, oC) for 30 May 2021: NGCD-1 on the left; NGCD-2 on the right.
Anchor figure10 figure10
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.
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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 Agreement signed on 11/11/2014 and Contribution Agreement signed on 22/07/2021). 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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