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changes.mady.by.user Iain Russell

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New Version 50

changes.mady.by.user Pedro Maciel

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  • U/V to u/v: convert spectral U/V to gridded u/v
  • vo/d to U/V (or u/v): convert spectral vo/d to spectral U/V or (gridded) u/v, if output is defined gridded (such as by specifying Grid).
  • Off: default

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  • Automatic: regular Gaussian grid, with N given as linear spectral order relation to output grid latitude increments
  • Source: octahedral reduced Gaussian grid, with N given as cubic spectral order relation to output grid latitude increments (mimics dissemination)
  • None: no intermediate grid, spectral inverse transform target is the user's intended output (costly if many different outputs are intended)
  • name of the desired intermediate grid

Extra processing

Nabla

Activates a nabla (differential) operator processing on the fields. Possible functions are:

  • Scalar Gradient
  • Scalar Laplacian
  • UV Divergence
  • UV Gradient
  • UV Vorticity
  • Off: do not perform any nabla operation

Nabla Poles Missing Values

Possible values are On and Off.

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Interpolation methods and parameters

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There is a high degree of customisation available to parametrise the available interpolation methods. Please note:

  • Not all the interpolation methods support all possible grid types
  • Even though the editor tries to avoid these, some inconsistent option combinations are allowed

Interpolation

Specifies the type of interpolation to be used on the fields. The default is Automatic, which selects either Linear or Nearest Neighbour based on an internal table of known parameters. If the parameter is unknown, the default will be Linear. The possible interpolation methods are:

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  • Climate Filter
filter for processing topographic data (see IFS documentation, Part IV: Physical Processes, 11.3.1 Smoothing operator)
  • Inverse Distance Weighting
IDW of the form distance-1; If input points match output point, only that point's value is used for output
  • Inverse Distance Weighting Squared
IDW of the form (1 + distance2)-1
  • Shepard
IDW of the form distance-p (option Distance Weighting Shepard Power, default 2.)
  • Gaussian
IDW of the form exp(- distance2 / (2 σ)2) (option Distance Weighting Gaussian Stddev, default 1.)
  • Nearest Neighbour
Emulate emulate Interpolation as Nearest Neighbour by picking first point (note that, when Nearest Method is Sample, a random nearest near point is picked)
  • No
no distance weighting, average input values (irrespective of distance)

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  • Distance Weighting Shepard Power: specify Shepard's method power parameter (see Wikipedia specific section)
  • Distance Weighting Gaussian Stddev: specify Gaussian standard deviation (see Wikipedia)

Non Linear

Possible values are:

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  • Missing If All Missing

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  • Missing If Any Missing

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  • Missing If Heaviest Missing

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  • Simulated Missing Value

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  • Heaviest

This treatment is applied after calculation of the interpolation weights, and before they are applied to input values to generate output values. This allows modifications of these weights based on input data, such as the presence of missing values — In any case, no missing values are ever used for interpolation.

Most of the options avaiable concern modyfing the set of input points weights pertaining to a specific output point. When removing interpolation weights (pe. because they point to a missing value) all the remaining interpolation weights are re-normalised (linearly) to sum(wi) = 1.

Possible values are:

  • Missing If All Missing
if all input point values (contributing to an output point) are missing, set output value to missing (it requires all input point values to be missing)
  • Missing If Any Missing
if any input point values (contributing to an output point) are missing, set output value to missing (it suffices one input missing value)
  • Missing If Heaviest Missing (default)
if the most significant point for interpolation (largest interpolation weight) is missing, set output value to missing;
Typically (but not generally) this corresponds to the nearest input point
  • Simulated Missing Value*
allows a user-specified value (option Simulated Missing Value) with a tolerance (option Simulated Missing Value Epsilon)
  • Heaviest
emulate Interpolation as Nearest Neighbour by selecting the most significant point for interpolation to each output point (discarding the other contributions)
  • No*
no non-linear corrections are applied

* In the presence of missing values this can can create wrong results.

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Associated options supporting Non Linear (described above):

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For GRIB-based LSM (this excludes '1km' and '10min'), the threshold for condition (value ≥ threshold) to distinguish land (true) from sea (false).

Nabla operators

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Nabla

Activates a nabla (differential) operator processing on the fields. Possible functions are:

  • Scalar Gradient
  • Scalar Laplacian
  • UV Divergence
  • UV Gradient
  • UV Vorticity
  • Off

Nabla Poles Missing Values

Possible values are On and Off.

Extra Processing

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Area

Supply a grid definition as described here: area - keyword in MARS/Dissemination request (swapping north/south).

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For example, this set of parameters generates the following output data:


Code Block
languagepy
t01 = mv.regrid(
    grid     = [0.1,0.1],
    area     = [31,-17,64,38],
    data     = t_2m
    )

mv.plot(t01)


Image Modified

Frame

Specifies the width of a frame within a given sub-area, as described here frame - keyword in MARS/Dissemination request.

The width of the frame is specified as an (integer) number of grid points inwards from a given area. The following plots show a sub-area with Frame= set to 8.

Image Modified

Image Modified

Rotation

Position of the South Pole of the intended rotated grid as lat/lon in degree, as described here: rotation - keyword in MARS/Dissemination request.

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