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This icon derives (and returns) a Hovmøller diagram data unit along a specified arbitrary transect line or a rectangular area. This application can be used to display a two-dimensional graph with latitude or height as one axis and time as the other. If an input line is given, point values for each field are interpolated along the transect line, with a spacing consistent with the resolution of the input GRIB data. If a rectangular area is given, average values for each field are taken along the North-South or East-West direction.

The Hovmøller data can be plotted (using a default visualisation and with the plot area based on the range of data values) or saved as a NetCDF data file.

The option Expand Hovm allows the production of Hovmøller diagrams to be computed incrementally. This could be useful, for example, if the input data is too large or the Hovmoeller diagram needs to be updated periodically (e.g. to produce a diagram operationally during a certain period of time).

If access to the output computed values is not required, or for more control of the plotting, use icon Hovmoeller View.

The macro language equivalents are mhovmoeller_area(), mhovmoeller_line(), mhovmoeller_vertical() and hovmoeller_expand() (depending on the type of Hovmøller chosen).


If the selected option is Area Hovm or Line Hovm and if more than one parameter and/or level is contained in the GRIB icon, Hovmøller Data returns a set of Hovmøller diagrams. However, if the selected option is Vertical Hovm, the GRIB icon should contain a set of levels for each parameter. Also, In this case if the input data is specified in model levels, you must include the parameter LNSP should you want the vertical axis of the plot in pressure levels rather than model levels when visualising the outputon ECMWF model levels and Vertical Level Type is "pressure" a fixed surface pressure value (1013.25 hPa) is used to determine the pressure on model levels.

Average Direction (Area Hovm)


Specifies if a conversion from model level to pressure level needs to be performed. Options are As In Data and Pressure, If if the conversion to pressure is selected and the input data is specified in model levels, the LNSP field should be added to the input data.

Netcdf Data (Expand Hovm)