Using the web application for download of scenario data

General information

The amount of data produced by climate models is very large. Data are stored in binary formats (e.g. GRIB, netCDF) that are not widely spread. To use data in these binary formats additional third-party software needs to be installed.

The purpose of the climate scenario data download application is to allow the user to download parts of the original datasets. This way the user can choose the variable, region and time period of interest and will not have to download large amounts of irrelevant data.

The application also provides the opportunity to convert data to a text format that can be used in common software, such as a text editor or Microsoft Excel.

About coordinate systems

In the regional climate model RCA, a rotated coordinate system is used. This means that the north and south pole in the model’s coordinate system are not the geographic north an south pole, but shifted in a certain way. This is a technical choice made to enable an as even spacing of the model’s longitudes and latitudes as possible, to achieve an even resolution in the regional model domain. When using the results in analysis or graphics in a regular grid, the data need first be transformed to the appropriate coordinate system.

The application map is presented in the model's rotated coordinate system. The position of the mouse pointer is however given in both the model's rotated coordinates and regular WGS84 coordinates. This way it should be possible to locate a known longitude-latitude point on the map.

The application text file output is converted to regular WGS84 coordinates. The netCDF-files use the rotated coordinate system, but include fields with regular WGS84 coordinates of each cell's center point for the chosen area.

Choosing area of interest

The map can be used to define the area of interest. Hold down the left mouse button and drag across the map to draw a rectangle. The coordinates of the corners will be transferred to the corresponding fields in the form below the map.

To show the model area, grid cells and calculation points in the map, check the corresponding check boxes.

There are also tools for zooming and panning the map. These are described on the download page.

Choosing output format

NetCDF (network Common Data Form) is a set of software libraries and machine-independent data formats that support the creation, access, and sharing of array-oriented scientific data http://www.unidata.ucar.edu/software/netcdf/. In order to use the netCDF-files some third-party software is needed. For example the netCDF format is supported by later versions of ESRI ArcGIS. There are also a number of free tools for viewing and manipulating netCDF-files. A good place to get started with netCDF is Wikipedia.

The text format provides data in an ordinary text file and with regular WGS84 coordinates. This can be a good option when just looking at data or working with a small amount. In the text files data values are rounded to one decimal. A text file is roughly twice as big as the corresponding netCDF-file.
Below is an example of a text file generated by the application.

scenario_txt_example

Each column (except the first) shows data for one grid cell. The first 10 rows are used to describe the regular WGS84 coordinates of the cell:

CPregLon: Longitude of the cells center point.
CPregLat: Latitude of the cells center point.
ULregLon: Longitude of the cells upper-left corner.
ULregLat: Latitude of the cells upper-left corner.
URregLon: Longitude of the cells upper-right corner.
URregLat: Latitude of the cells upper-right corner.
LLregLon: Longitude of the cells lower-left corner.
LLregLat: Latitude of the cells lower-left corner.
LRregLon: Longitude of the cells lower-right corner.
LRregLat: Latitude of the cells lower-right corner.

The following rows show the date in the first column and the data values for each point in the rest of the columns.

Importing to Microsoft Excel

The process of importing text data into Microsoft Excel is a bit depending on software version and operating system, but generally this should work:

  • Start Microsoft Excel.
  • Choose file->open and then navigate to the text file. The text import wizard should appear.
  • Check "delimited" and click Next.
  • Check "Tab" and "Space" and click Finish.

One problem that might occur (typically for Swedish users) is that the data text files use decimal point as separator. If the operating system uses comma as decimal separator Microsoft Excel might be unable to interpret the file correctly. One way of solving this is to simply replace all points with commas using a text editor. To avoid doing this at every import another solution is:

  • Open Windows control panel. (click Start->Settings->Control Panel)
  • Double click "Regional and Language Options".
  • Choose the tab "Regional Options" and click the Customize button.
  • Choose the tab "Numbers", enter a point in the field for "Decimal Symbol" and click OK.