Reanalyses

The Twentieth Century Reanalysis (20CR) and CERA-20C both reconstruct past climates assimilating only surface observations (they also use SST and sea-ice fields from datasets like HadISST). The success of these products has dramatically increased the value of sub-daily observations, particularly of surface pressure.

Sample reanalysis fields (MSLP) depending on observations (yellow dots). Source

The long reanalyses are perhaps the most obvious and immediate customers for digitisation. 20CR in particular has demonstrated a strong relationship between availability of nearby observations and reanalysis skill, and shown case studies linking digitisation work to improvements in the analysis.

The reanalyses need sub-daily observations (particular of station pressure or MSLP, though there is research ongoing into assimilating other variables). They also use sea-surface-temperature observations from ships, either indirectly - via SST datasets - or directly - in coupled assimilation.

While these are global datasets, there is much opportunity to improve them in the vicinity of the UK. There are few digitised pressure observations around the UK before about 1950, and ‘preliminary studies indicate that digitising more would prodiuce dramatic improvements in the reanalysis quality in this region. The DWR records would be particularly well suited to this work.

This is an active and successful area of work, and additional digitisation could make a big difference in the qualiy of the reconstructions around the UK. We should give the digitisation required for this a high priority.