A daily series of mean sea-level pressure for London, 1692-2007

This paper presents a new 300-year daily series of Mean Sea-Level Pressure (MSLP) for the city of London. Daily barometer readings recorded in the vicinity of London were digitised from several sources and by joining these data with previously available data, a near-continuous series was constructed to span the period 1692–2007. The data were quality controlled and then corrected to represent daily means of MSLP at standard modern-day conditions. This series was then subjected to a statistical homogenisation procedure. The Penalized Maximal t-test was used with several reference series to identify breakpoints in the series over the period 1780–2007. In the absence of suitable reference series, the homogeneity of the earlier 1692–1779 period was tested using the Penalized Maximal F-test. Both tests were implemented through the RHtestV2 software on the monthly and annual means derived from the daily data. The majority of the identified breakpoints could be supported by meta-data and most occur at the juncture of the component series. A major feature of the homogenised series is that the long-term mean is 1.2 hPa lower than that of the previous monthly series for London created under the EU ADVICE project for the period 1774–1999. The long-term mean of 1015.2 hPa for the new series is more consistent with other long MSLP series in the UK.