RN WW2 Observations index
NAT Diagnostics for the new marine obs
We hoped that the new observations would allow us to improve on HadNAT2 (night marine air temperatures derived from ICOADS2 obs.) in the same way as SST: better coverage and new information on biases.
Coverage
The figure below shows the improvement in coverage given by the new obs. The plot is the extra fractional coverage provided by the new obs (fraction of months during 1938 and 1941-7 (1938-47 with 1939 and 1940 removed), for each 5x5 degree square, where there are new obs but no ICOADS obs.) The increase is clear over most of the Atlantic and Indian Oceans, and largest around the African coast, in the Western Indian Ocean, the Mediterranean, and the UK coastal waters. The coverge increase is much the same as for SST.
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| Fractional improvement in NAT coverage (1938 and 1941-7). |
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For more detail, see the
month-by month comparisons.
The next figure shows the global number of observations and total fractional coverage both before and after adding the new observations.
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| Coverage and number of observations with and without the new observations. |
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Differences between new obs and HadNAT2
Difference fields between HadNAT2 and the new observations have been calculated for
each month. The figure below is the mean of the monthly differences over 1938 and 1941-7. No bias adjustments have been applied to either dataset over this period.
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| Mean diffs: new-HadNAT2 (1938 and 1941-7). |
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The new data are systematically warmer than HadNAT2.
The next figure is a time series comparing monthly global average NAT anomaly from HadNAT2 (version with no bias adjustments) and the new data (not bias adjusted). The large WW2 bias in HadNAT2 is well known (attributed to measurements being made indoors, as lights could not be shown on deck), the same bias appears to be present in the new data, but it is constant - not limited to the war years.
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| Global mean from HadNAT2 and the new observations. |
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