RN WW2 Observations index
DAT Diagnostics for the new marine obs
The daytime air temperatures are not used as they are biased by ship heat island effects. But it's useful to compare them with nightime (
NAT) data.
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 (i.e. 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 DAT 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 ICOADS2 DAT
Difference fields between DAT drived from the ICOADS2 obs 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-HadDAT2 (1938 and 1941-7). |
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The new data show no obvious systematic biases compared to ICOADS2 obs.
The next figure is a time series comparing monthly global average DAT anomaly from ICOADS2 obs (with no bias adjustments) and the new data (not bias adjusted). Again, there are no obvious systematic differences between the old and the new obs, except for a one-off point in december 1940, which is probably a random effect - the number of new observations in that month is very small.
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| Global mean from HadDAT2 and the new observations. |
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