You are viewing an old version of this page. View the current version.

Compare with Current View Page History

« Previous Version 3 Next »

MARS

Specifies the target grid which can be either a Gaussian or a Latitude/Longitude grid.

grid=<value>

MARS requests specifying grid=av will return the archived model grid. For Latitude/Longitude output, the format is in degrees, i.e. grid = 2.5/2.5, where the first number denotes the east-west resolution (longitude) and the second denotes the north-south resolution (latitude). The grid spacing needs to be an integer fraction of 90 degrees (latitude range from the Equator to the Pole), e.g. 0.225, 0.25, 0.28125, 0.3, 0.4, ...

Output on a Gaussian grid is specified by a letter denoting the type of Gaussian grid followed by an integer (the grid number) representing the number of lines between the Pole and Equator, e.g. 

  • grid = F160  - full (or regular) Gaussian grid with 160 latitude lines between the pole and equator
  • grid = N320  - ECMWF original reduced Gaussian grid with 320 latitude lines between the pole and equator, see Reduced Gaussian Grids for grid numbers used at ECMWF
  • grid = O640 - ECMWF octahedral (reduced) Gaussian grid with 640 latitude lines between the pole and equator

Not all grid names and grid number combinations are supported. Currently, the Gaussian grid names and numbers supported for MARS retrievals are:

Octahedral reduced Gaussian (O grids)O1280O640O512O400O320O256O200O160O128O96O64O48O32
Original reduced Gaussian  (N grids)
N640N512N400N320N256N200N160N128N96N64N48N32
Regular (Full) Gaussian (F grids)F1280F640F512F400F320F256F200F160F128F96F64F48F32

MARS requests specifying an unsupported grid will fail. For example, a retrieval request with grid=O123 will return an error.  If the letter denoting the type of Gaussian grid is omitted, e.g. grid=320, a full (or regular) Gaussian grid with 320 grid lines is returned.

For other keywords controlling the interpolation see the diagram below.

Examples

grid = av,           # will return the archived model grid
grid = 0.125/0.125,    # will return an 0.125 x 0.125 deg longitude/latitude grid
grid = F320,                 # will return a full Gaussian grid with 320 latitude lines between the pole and equator

Dissemination

Specifies the output grid which can be either a Gaussian or a Latitude/Longitude grid.

grid=<value>

Products on latitude-longitude grids are interpolated from the spectral or (quasi regular - reduced) Gaussian grid associated with the ECMWF forecast model. Interpolation is made to a 0.125 degree latitude-longitude grid and resulting products are generated by selecting required points. Regular Gaussian grids are also available. Where appropriate, the interpolation to a latitude-longitude grid uses a land/sea mask so that an interpolated land point is assigned a value calculated using only neighbouring land grid points, and an interpolated sea point is assigned a value using only neighbouring sea grid points. For precipitation fields, the interpolation assigns a zero value if the value at the nearest grid point is zero; also any value within one per cent of the global minimum for the field is taken to be equal to zero.

Products on polar stereographic grids are interpolated from the 0.125 degree latitude-longitude interpolated fields; thus they are subject to a double interpolation error.


  • No labels