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MOHMAT, (Met Office Historical Marine Air Temperature) is a gridded dataset of marine air temperature anomalies covering the period 1856-present. The current version of the dataset is MOHMAT4, which is described in paper below.
MOHMAT4 has been updated to produce MOHMAT43N and HadMAT1 both of which are described in the references.
MOHMAT is produced by taking in-situ measurements of MAT from ships and buoys, rejecting measurements which fail quality checks, converting the measurements to anomalies by subtracting climatological values from the measurements, and averaging the resulting anomalies on a 5 by 5 degree monthly grid. Note that only night-time data are used, because day-time data are corrupted by heat island effects. See the references for details.
Up to 1996 the measurements used are those in the U.K. Marine Data Bank; more recent years use data coming in through the GTS. MOHMAT is no longer updated.
After gridding the anomalies, bias corrections are applied to remove spurious trends caused by changes in ship deck heights and various unusual operational practices, and the data are smoothed to reduce noise.
An optimal interpolated version of this dataset, HadMAT1, is also available. It has been shown to be better than the non optimally interpolated NMAT data when it exists for very many applications (see references for details).
MOHMAT43N represents and improvement to the ship deck height corrections used in MOHMAT42N and is available here.
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