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

The Hovmoeller Data Editor

The Hovmøller Data editor belongs to a type of editor known as family editor, which allows related sets of input specifications to be grouped in the same icon editor, each in its own tabbed pane. The available input panes are:

Line Hovm     - Provides input for Hovmøller diagrams derived from an input transect line.

Area Hovm     - Provides input for Hovmøller diagrams derived from an input rectangular area.

Vertical Hovm - Provides input for Hovemøller diagrams derived from an input rectangular area and a set of levels.

Expand Hovm - Provides input for expanding Hovmøller diagrams that have been derived previously.

To operate with this icon first select one of the above options by clicking the appropriate menu option from the Application parameter.

Line (Line Hovm)

Specifies the coordinates of a transect line along which the Hovmøller diagram is calculated. Enter the coordinates (lat/long) of a line separated by a "/" (lat1/long1/lat2/long2). Alternatively, use the coordinate assist button.

Area (Area Hovm or Vertical Hovm)

Specifies the coordinates of the area over which the Hovmøller diagram is calculated. Enter the coordinates (lat/long) of an area separated by a "/" (top left lat and long, bottom right lat and long). Alternatively, use the coordinate assist button.

Data

Specifies the data (GRIB icon) from which to derive the Hovmøller diagram. The input GRIB icon must specify a time-series of a meteorological variable in a latitude-longitude or Gaussian grid. The assist button provides a default MARS Retrieval icon that you can be modified to suit user requirements.

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 Height Hovm, the GRIB icon should contain a set of levels for each parameter.

Average Direction (Area Hovm)

Specifies the direction along which the averaging of the variable is performed. Options are North South and East West. For North South, the averaging is weighted by cos(latitude).

Swap Axes

By default, the definition of the vertical and horizontal axes of the Hovmøller diagrams follows pre-defined rules. However, if Swap Axes is set to Yes then the axes will be swapped around.