What is GRIB?
The GRIB icon
GRIB files are represented by this icon in the user interface:
Examining GRIB contents
The contents of a GRIB file can be inspected with the GRIB Examiner, which can be started up from the user interface (right-click examine on the icon).
Visualisation on maps
GRIB fields (with the exception of spherical harmonics fields) can be directly visualised in Metview on a map view. In the user interface just right-click visualise on the icon to get a plot with the default settings. GRIB map plots can be further customised with the Contouring or Wind Plotting icons for scalar fields or vector fields, respectively.
Visualisation on other views
As well as the map-based visualisation, we can also generate the following plot types from GRIB data:
- vertical cross sections (see Cross Section Data and Cross Section View)
- zonal and meridional averages (see Average Data and Average View)
- Hovmoeller diagrams (see Hovmoeller Data and Hovmoeller View).
Filtering and interpolation
The GRIB Filter icon provides the means to select a subset of fields from a GRIB file. It (and the MARS Retrieval icon) also contains some parameters, such as Grid and Area, which allow for interpolation to a new grid.
There are quite a few icons available in Metview to process GRIB data. These include the icons mentioned above and the following other icons:
- Relative Humidity
- Rotational or Divergent Wind
- Potential Temperature
- Simple Formula
- Velocity Potential or Stream Function
- Grib To Geopoints and Geopoints To Grib
Metview's script interface provides access to all these icons and also offers a rich set of functions and operators to work with GRIB data (see Script language support below).
Retrieval from MARS
If Metview has been configured with access to ECMWF's MARS archive, GRIB data can be retrieved via the Mars Retrieval icon. At ECMWF, MARS access is set up on all computer systems, while outside ECMWF the MARS Web API could be used in Metview (see the setup instructions here).
Script language support
Metview provides full support for GRIB from its Macro and Python interfaces. In script, GRIB data is represented as a fieldset. Fieldset handling is probably Metview's richest and most powerful interface including (on top of the icon functions):
- high-level field arithmetic
- filtering and interpolation
- masking, bitmaps
- GRIB header and value access and modification
- statistics, horizontal aggregations and vertical computations
- and many more ...