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An example demonstrates this. Say you wanted to defined a straight-line cross-section from 60S/25E to 60S/155W. This would be specified as -60/25/-120/25. The fact that one of the latitude values is below -90 indicates to Metview that a cross-section going through the South Pole is desired. Once this has been established, the fact that the two longitude values are identical tells Metview to use a straight line through the pole. If this is the intent, then only one unique longitude value is required, as the other one can be deduced. Giving Metview two different longitude values will cause a cross-section consisting of two curves to be produced.
Wind Parallel
When this option is On, the wind components are projected onto the cross section plane. For 2D wind the result is a signed scalar data (a contour plot). When 3D wind data are available a vector plot is produced with the vertical component scaled/computed as specified in parameter W Wind Scaling Factor Mode. Valid values are On/Off.
Wind Perpendicular
When this option is On, the wind components are projected onto the normal vector of the cross section plane. The result is a signed scalar data (a contour plot). Valid values are On/Off. This cannot be set to On if Wind Parallel is also On.
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Specifies the ecCodes paramId of the vertical wind component data. The default value is 135 i.e. pressure velocity (as used by ECMWF).
T Param
Specifies the ecCodes paramId of the temperature data used in the vertical wind computations when W Wind Scaling Factor Mode is set to Compute. The default value is 130 (as used by ECMWF).
Horizontal Point Mode
Specifies how the geographical points along the input transect line will be computed. Valid values are Interpolate and Nearest Gridpoint. Setting this option to Interpolate will create a regular set of interpolated geographical points along the transect line. Setting this option to Nearest Gridpoint will instead select the nearest points from the data.
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W Wind Scaling Factor Mode
Specifies the representation of the vertical wind component (defined as W Wind Param). The valid values are as follows:
- Automatic: the values are scaled by a factor based on the geographical area, the top/bottom pressure levels and the size of the plot window.
- User: the values are scaled by the factor defined via parameter W Wind Scaling Factor.
- Compute: in this mode, supposing that W Wind Param defines the the pressure velocity, the vertical wind component in m/s is computed using the following hydrostatic formula:
| Mathdisplay |
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w = |
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- \frac{\omega R T}{p g} |
where:
- omega
- ω: pressure velocity (Pa/s)
- p : pressure on (Pa)
- T: temperature (K)
- R: gas constant, 287.058 J kg-1 K-1
- g: gravitational acceleration, 9.81 m/s2
To make this formula work, the input data have to be specified either on pressure levels or on model levels together with LNSP. The temperature's paramId is defined by T Param. When temperature is not available, the computations still work but T is replaced by a constant 273.16 K value in the formula. Having computed the vertical wind component, a scaling with the factor defined by W Wind Scaling Factor is still applied to the resulting values.
The default value is Automatic.
W Wind Scaling Factor
Specifies the vertical wind scaling factor if W Wind Scaling Factor Mode is set to User or Compute. The default values is -100.
Level Selection Type
Specifies the method to define the output pressure levels when converting model level data to pressure levels. Options are:
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