Diurnal variability of water vapour in the Baltic Sea region according to NCEP-CFSR and BaltAn65+ reanalyses**The survey was supported by the Estonian Science Foundation under a postdoctoral grant JD189, by European Social Fund’s Doctoral Studies and Internationalisation Programme DoRa and project SLOOM12073T, which are carried out by the Archimedes Foundation, and by the Estonian Radiation Climate project, funded by the European Regional Development Fund.

AbstractDiurnal variations in water vapour in the Baltic Sea region are examined using BaltAn65+ and NCEP-CFSR reanalyses of summer (JJA) data for the period 1979–2005. A systematic difference between precipitable water (PW) diurnal variability above the land and the water is revealed. Above the land, PW diurnal variability has minimal values at 00 and 06 UTC, as in previous studies, whereas above the water, the minima are at 12 and 18 UTC. Diurnal variability in the vertical humidity profile is controlled by turbulent mixing and the diurnal behaviour of sea breezes. The impacts and proportions of diurnal variability of humidity are evaluated at different vertical levels