Improved Historical Analysis of Oceanic Total Precipitable Water*

The amount of water vapor in the atmosphere, total precipitable water (TPW), is an important part of the global water cycle, and a clearer understanding of ocean-area TPW is critical for understanding climate variations. This study uses satellite-period statistics and historical data to analyze monthly oceanic TPW beginning in the nineteenth century. Input data for analyzing the historical TPW includes outputs from an extended dynamic reanalysis and estimates of TPW based on historical sea surface temperature (SST). Methods are developed to optimally use the various inputs to produce an improved analysis. Cross-validation testing is used to guide analysis development. Some evaluation of the resulting analysis indicates several strong climate modes. A global mode indicates multidecadal increases in TPW since the nineteenth century, with strongest increases in the tropics and adjacent to land monsoon regions. Strongest multidecadal changes in the global mode are 1910-40 and since 1980. An ENSO mode for the extended period indicates a trend since the 1980s, opposite to the tendency in the global mode. There is no apparent multidecadal variation in the ENSO mode before 1980, suggesting that its multidecadal relationship with the global mode can change. Analysis of SST over the same period shows climate modes consistent with the TPW modes, and for the satellite period there are consistent variations in the satellite data, showing the strong link between SST and oceanic TPW.