About DMI’s Climate Data
By definition climate data is meteorological observation data, which are more than an hour old. DMI's climate data undergoes quality control by our climatologists, through which data is checked and erroneous data is removed. In addition to the quality controlled climate data, there are several additional parameters available, which are not quality controlled, but is useful to the agricultural sector.
DMI's climate data consists of data from Denmark (DNK) and Greenland (GRL). There are, however, some differences between datasets and data availability for Denmark and Greenland, respectively. Furthermore there are some key differences in how quality control is performed for Denmark and Greenland. One of the differences is that for Denmark data gaps in time and location are patched by interpolating from nearby stations, whereas for Greenland erroneous data are removed and data gaps may occur.
The Climate Data service consists of different spatial resolutions as represented in the table below.
| Data sets | Available for Denmark | Available for Greenland | Comment |
|---|---|---|---|
| stationValue | x | x | |
10kmGridValue | x | - | |
| 20kmGridValue | x | - | |
| municipalityValue | x | - | |
| countryValue | x | - |
About stationValue
stationValue is quality controlled meteorological observation data for Denmark and Greenland on station level and derived values such as daily, monthly and yearly values which have been calculated for all stations. In addition to the quality controlled data, there are several additional parameters available, which are not quality controlled, but are used by the agricultural sector. For an overview of which parameters are available in the different time resolutions, please see the parameter list. The stations available for the stationValue service can be seen here. stationValue is available from a stations start date until the termination date of the station.
There are some key differences between stationValue for Denmark and Greenland respectively, as shown below:
| Denmark | Greenland | |
|---|---|---|
| Frequency of manual quality control | daily*, monthly, yearly | monthly |
| Method | Visual control by inspection of interpolated grid maps on which the station data plotted Visual inspection of station series time plots | At the beginning of every month, all data from the previous month is manually checked from time series plots |
| Complete time series | yes (interpolation algorithm is applied to fill in data gaps and replace erroneous data) | no (erronuous data is removed, an interpolation algorithm is not applied on the Greenland data, due to the complicated circumstances of the large geographical area, complex topography and low station density. In certain cases erroneous data is replaced by a manually estimated value) |
* The manual daily QC entails that data usually is available on the next week day after observation time.
Quality Control
Meteorological observation data may contain various errors and data outages. When potential errors are identified they are investigated closely. For example by looking at raw observation data or including other data sources such as nearby stations or other parameters which can help to conclude whether the data must be excluded. Errors are typically due to malfunction of instruments caused by wear and tear or exposure to weather and on rare occasions vandalism.
Typical errors in the observations are unrealistically high or low outliers or small but consistent biases. Furthermore certain stations can be misleading for longer periods, if the station observes data deemed unrepresentative by DMI's climatologists.
Quality Control DNK
stationValue for Denmark undergoes manual quality control on multiple levels:
- Spatial controls on a daily, monthly and yearly level are performed by visually inspecting interpolated grid maps on which the station data plotted
- Visual control of the station series are preformed based on time plots
Erroneous or missing data values are filled in by interpolated values derived from surrounding data.
The manual daily QC entails that data usually is available on the next week day after observation time.
About yearly quality control
Climate data from DMI’s open data is quality controlled daily, monthly and annually, and is usually ready in February. Unfortunately, the quality control status (qcstatus) does not indicate whether or not the data has undergone the yearly quality control. Release notes for the climate data service will be updated, when data has undergone the yearly quality control.
For waste management data packs (danish: deponipakker), DMI recommends to first download the data after it has undergone the annual quality control. Waste management data packs (danish: deponipakker) usually include wind direction, wind speed, mean temperature, precipitation, potentiel evaporation, and relative humidity.
Quality Control GRL
stationValue for Greenland undergoes manual quality control to ensure the data quality:
- At the beginning of every month, all data from the previous month is manually checked from a time series plot
- Identified erroneous data will be labeled as excluded (see validity property here)
- In certain cases erroneous data is replaced by a manually estimated value
Excluded values are not included in derived values. Derived values contain information on the amount of data behind the calculations.
Time resolutions and Types of Days
Station values are available in the following time resolutions:
- Hour
- Day
- Month
- Year
Station values are derived from meteorological observations and represent a parameters value in a specific time interval. For example, the mean temperature of the day November 3rd 2012 for a given station.
However, the exact time a certain time resolution begins and ends depends on the time zone, and how the time resolutions above are defined. Due to historical reasons the time resolutions can differ for the different parameters. Time resolutions also differ between stations values for Denmark and Greenland
The response properties from and to will tell you the exact time interval covered by the station value. If you want to query for station values in a specific time time interval, you will need to know how time resolutions and types of days work.
Hour
Hourly station values are always in UTC. This avoids any confusion that might arise if summer- and winter time was used. The API supports querying time ranges with time zones, so no special knowledge is needed for querying hourly values in a specific time range.
Day
Daily station values operate with different definitions of what a day is. The different definitions can be seen below.
| Type of day | Description |
|---|---|
| Local day | from/to midnight in local time with changes to summer and winter time |
| Old meteorological day | a day which covers the hours from 6:00 am to 6:00 am next day in UTC |
| Manual precipitation day | a day which covers the hours from 12:00 pm to 12:00 pm next day in UTC. It is only used by a few stations on Greenland, where precipitation data is manually measured. |
| The exeption to the rule | only used by the parameter of maximum precipation in 30 minute intervals. This is defined as the local day, but also includes the 30 minutes before midnight, so the maximum precipation at midnight is included. |
The type of day used for a station value, depends on the parameter of a station value. You can see a list of which parameters use which type of day here.
Month
Monthly station values are derived from daily station values. They begin when the first day of the month begins, and end when the last day of the month ends.
Example:
The monthly station value for the parameter mean_temp in March 2018 for a Danish station would represent the time range: 1/3/2018 00:01 CET - 31/3/2018 24:00 CEST. Notice the change to summertime, which happens in Denmark on the last Sunday of March.
Even if a parameter has monthly station values but not daily values (as per the parameter table), the month still begins and ends at the time as the first and last day would have begun and ended if they existed.
Year
Yearly station values are derived from daily station values. They begin when the first day in the year begins (January 1st), and end when the last day in the year ends (December 31st).
Example
The yearly station value for the parameter mean_temp in 2018 for a Danish station would represent the time range: 1/1/2018 00:01 CET - 31/12/2018 24:00 CET.
Even if a parameter has yearly station values but not daily values (as per the parameter table), the year still begins and ends at the time the first and last day would have begun andended if they existed.
About Spatial Resolutions (10kmGridValue, 20kmGridValue, municipalityValue, countryValue)
The climateData service also includes data in different spatial resolutions for Denmark. The data is based on station data from Danish stations, which is interpolated into a 1x1km grid net covering all of Denmark’s land area using a modified inverse-distance algorithm. The calculated values in each grid cell depends on the values of the nearest surrounding station found in 8 sectors. One value is calculated for each area (e.g. one municipality) from the grid cells covering the jurisdiction area combined with a weighting of how much of each grid cell is within the area. The stations are weighted in relation to the distance and climatological comparability (distance to sea) to the grid cell. Aggregated grid cells are used to compile datasets of different spatial resolution.
The different spacial resolutions are calculated/derived from stationValue data as it becomes available. The data is recalculated when the quality controlled stationValue data has been quality controlled by our climatologists. In some instances area data is based on additional parameters, which are not quality controlled. Please see the parameter list for an overview over which parameters are available and whether or not they are quality controlled by our climatologists.
Spatial resolutions are not available for Greenland, as an interpolation algorithm cannot be applied due to the complicated circumstances of the large geographical area, complex topography and low station density.
| Spatial resolution | Description | |
10kmGridValue | climate data in a 10 x 10km grid resolution covering danish land areas For your convenience DMI has created an interactive web page map to inspect the grid here. You can also see, how you can import grid identification layers into Qgis. | |
| 20kmGridValue | climate data in a 20 x 20km grid resolution covering danish land areas For your convenience DMI has created an interactive web page map to inspect the grid here. You can also see, how you can import grid identification layers into Qgis. | |
| municipalityValue | climate data for the Danish municipalities | |
| countryValue | climate data for Denmark |
Read more about the spatial resolutions here.