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).
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 Vertical Hovm, the GRIB icon should contain a set of levels for each parameter. In this case if the data is specified on 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 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.
Resolution
Used to interpolate the data onto a regular grid, and applies to both the horizontal and vertical axes where appropriate. This parameter is essential for creating a Hovmøller diagram from satellite data.
Vertical Level Type (Vertical Hovm)
Specifies if a conversion from model level to pressure level needs to be performed. Options are As In Data and Pressure, if the conversion to pressure is selected and the input data is specified in model levels.
Netcdf Data (Expand Hovm)
Specifies the data (Netcdf icon) from which to expand the Hovmoeller diagram.
Netcdf Path (Expand Hovm)
Specifies the Netcdf file path and name. Type the full file path and name. Alternatively, parameter Netcdf Data can be used.
Data Path (Expand Hovm)
Specifies the Grib file path and name. Type the full file path and name. Alternatively, parameter Data can be used.