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  Definitions for global map plots


Global plots of various diagnostics, for processed near-real time AATSR data, are produced daily. These global plots are produced by averaging the 10 arc minute data to a 1 degree resolution. Global plots displaying the averaged data over the previous month are also displayed. Only SSTs which pass certain quality control tests are included in these analyses: they must be deemed to not be cloud contaminated, from threshold tests against the number of pixels contributing to each cell, and from threshold tests against climate datasets. Checks are also performed to test for the presence of ice in the cell, with positive results rejected. Finally, a mean global offset is added to the SST, differing for 2-channel and 3-channel retrievals, to correct for mean biases observed between the retrieval algorithms and against in situ SST data. Explanations of the different plots produced are given below.

Sea surface temperatures

The skin SST (the temperature of the ocean in the top couple of millimetres) is estimated from AATSR brightness temperatures. These skin SSTs are then used to estimate the bulk (or sub-surface) SST at approximately one metre below the sea surface using a skin effect model applied at the Met Office. Global maps of these SSTs are displayed. Details of the form of the plotted maps are listed:

  • Bulk (sub-surface) SST originating from skin observations using dual-view 2-channel retrieval algorithms (day & night).
  • Bulk (sub-surface) SST originating from skin observations using dual-view 3-channel retrieval algorithms (night only).
  • Skin SST from dual-view, 2-channel retrieval algorithms (day and night observations).
  • Skin SST from dual-view, 3-channel retrieval algorithms (night observations only).

In addition, global maps of the ESA supplied dual-view skin SST are also plotted. Mean global offsets are not added to these SSTs.

Comparisons with HadISST1

Global maps are produced where the bulk SST estimated at the Met Office is compared against the 1 degree HadISST1 dataset. Global maps of the means over each grid box are displayed. Similar maps are produced for comparisons of the ESA supplied skin SST product against HadISST1.

The bulk SST field used within the comparisons is formed by combining the day-time bulk SST 2-channel retrievals with the night-time bulk SST 3-channel retrievals, only when a good skin deltaT (the modelled difference between the skin and bulk SSTs) has been calculated. The HadISST1 dataset comprises both insitu and AVHRR observations interpolated into 1 degree grid boxes and is supplied in monthly files, with a month's delay. Follow this link for more information on Met Office climate datasets.

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