Given 28 gridded datasets and a variety of novel things to try, I be flummoxed. Try this
The new dataset kid on the block, seems to have appeared 6th June is Met Office Hadley Centre HadNMAT V2, nighttime marine air temperature. Grided at 5 degrees.
Figure 1, an experimental plot from data generated by alpha software. So far as I know this is correct. The main graphic is a hovmoller plot intending to show how the contribution to a global temperature computation has varied spatial with time.
Looking at that lets eyeball a month where there seems more southern data, typed in 1890, left the month at 4 from something else, random,
Figure 2, the active gridcells. We can see the pattern of shipping traffic used for the dataset. Both the Suez canal and both Capes in use, not Panama Canal. Trade and military activity in Indochina shows.
The pattern will change as technology, trade and warring tribes take their toll.
Out of idle curiosity, see that red cell off Newfoundland? The Atlantic is well covered so lets extract the time series, one better all 9 cells as a block with 47.5N 47.5W at the centre. Easy to work out cell centres via the PDF plot, or can plotted with annotation.
Figure 3, Set of 9 gridcells of 5×5 degrees.
Figure 4, plot of gridcell time series in one.
Ships rarely sail in a circle for a month yet these are monthly data points. Sharp temperature differences between adjacent cells are improbable, the scatter is huge.
Figure 5, Standard Deviation for the 9 cells against time. WWI and WWII are obvious. Consistent it is not.
Sorry about being boring, obsessive, takes a lot of persistence to the exclusion of all else to do significant software.
Post by Tim