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The target field needs to be gridded , therefore keyword grid should also and should therefore 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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. Latitude/longitude coordinates must be given as signed numbers
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as follows:
- north latitudes (i.e. Northern Latitudes (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. west must be given as positive numbers
- Western longitudes (east of the 0 degree meridian) being negative (must be given as negative numbers
If the longitude values overlap, e.g
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. 0 and 360 or -180 and 180, the eastern line of points will not be returned.
| value | comment |
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North/West/South/East | latitude/longitude coordinates of sub-area |
E |
A European area pre-defined as 73.5/-27/33/45 can be specified as letter "E".
| value | comment | ||
|---|---|---|---|
E | Same as area=specifies the European area | 73.5/-27/33/45 | |
G | specifies the global area 90/0/-90/360 (default) | North/West/South/East | latitude/longitude coordinates of sub-area
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 MARS (with MIR) can work with 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 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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GRID=1.0/1.0
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 .
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and includes a point at latitude=0, longitude=0.
Area examples
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| 73.5/-27/33/45 | |||
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| NORTH = 75° | WEST = 10° | SOUTH = 30° | EAST = 40° |
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specifies a frame three grid points wide with the outer limits 74/60/10/-20 and inner limits 72/58/8/-18.
For observations, the area keyword is used as a filter.
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