HISKLIM-COADS - final report.

The availability of a – though limited – number of Dutch meteorological ship logbooks from the period 1854-1938 and the accessibility of several archived documents and manuals gave the opportunity to investigate the methods of measuring sea level pressure on board ships and describe the practice of processing the recorded data afterwards. In Wallbrink et al. (2003), we showed that from the very start of the marine meteorological data acquisition, from 1854 onwards, the Dutch procedure for pressure reduction was consistent throughout. This cleared up the doubts that were attributed to the Dutch marine sea level pressure observations covering the period 1854-1938. As a result 5.7 million Dutch marine sea level pressure observations are now incorporated in ICOADS release 1c climatology. We present more background information about the used barometer corrections and the quality of the Dutch marine sea level pressure data, used in ICOADS. Unfortunately we determined that the Dutch ship logbooks, containing additional meta data, are presumed to be lost forever.