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MARS
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Specifies the desired sub-area of the data to be extractedretrieved.
area=<value> |
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For If specified for fields, the specification of the area keyword requests a will trigger some post-processing. The input fields to this operation can be
- spherical harmonics
- regular lat/lon grids
- global regular Gaussian grids
- global reduced Gaussian grids, including the octahedral reduced Gaussian grid
- wave fields
The As the target field needs to be gridded , therefore keyword grid it should also be specified in the same request using the keyword grid.
A horizontal sub-area is in general defined by a list of its latitude/longitude coordinates North/West/South/East in decimal degrees. If South > North, the values are swapped and a warning issued; southern latitudes and western longitudes must be given as negative numbers:
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automatically swapped. Latitude/longitude coordinates must be given as signed numbers
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as follows:
- north Northern latitudes (i.e. north of the equator) being positive (e.g: 40.5)south latitudes (i.e. must be given as positive numbers
- Southern latitudes (south of the equator) being negative (e.g: -50.5)Longitude values must be given as signed negative numbers, with:
- east Eastern longitudes (i.e. east of the 0 degree meridian) being positive (e.g: 35.0)west longitudes (i.e. must be given as positive numbers
- Western longitudes (west of the 0 degree meridian) being negative (e.g: -20.5)
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- must be given as negative numbers
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North/West/South/East | latitude/longitude coordinates of sub-area |
E | specifies the European area 73.5/-27/33/45 |
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Same as area=73.5/-27/33/45
G | specifies the global area 90/0/-90/360 (default) |
If the longitude values overlap, the most eastern line of points will not be returned, e.g.
AREA=90/-180/-90/180, |
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will return a field with the boundaries 90/-180/-90/179.5.
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Areas can be defined to wrap around the globe, e.g. in order to retrieve all longitudes but Europe one would specify area=75/60/10/-20.
If the area and the specified grid spacing do not match, the area boundaries will be moved inwards onto an underlying global grid with a point at latitude=0, longitude=0.
For observations, the area keyword is used as a filter.
MIR can work with MARS (with MIR) also supports shifted grids, with no point at latitude=0, longitude=0. An example would be:, e.g.
AREA=89.5/0.5/-89.5/359.5, |
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This is done automatically provided the differences between N-S and E-W limits are both divisible by the corresponding grid increments without remainder. 
In this example, the black points represent the original grid with 1 degree spacing. The red points show the user defined area, which has the same spacing but shifted by half a degree. MARS will honour the user defined area and return the inner grid shown in green.
In cases where the differences between N-S and E-W limits are not divisible by the corresponding increments without remainder, MARS with MIR starts from the user-specified south-west corner and goes up to (but does not exceed) the north-east corner. For example, a request specifying:
AREA=55.5/0.5/45.0/5.0, |
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retrieves AREA=55.0/0.5/45.0/4.5 with the northern and eastern boundaries adjusted so that the area returned lies within that specified by the request and includes a point at latitude=0, longitude=0.
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| NORTH = 50° | WEST = -135° | SOUTH = -60° | EAST = -35° |
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area=74/60/10/-20,
grid=1/1,
frame=3,
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Area examples
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For observations, the area keyword is used as a filter.
Dissemination
The keyword is used as with MARS, but mandatory in disseminationspecifies a frame three grid points wide with the outer limits 74/60/10/-20 and inner limits 72/58/8/-18.
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