Reduced Space Optimal Interpolation of Historical Marine Sea Level Pressure: 1854–1992*

Near-global 48 3 48 gridded analysis of marine sea level pressure (SLP) from the Comprehensive Ocean– Atmosphere Data Set for monthly averages from 1854 to 1992 was produced along with its estimated error using a reduced space optimal interpolation method. A novel procedure of covariance adjustment brought the results of the analysis to the consistency with the a priori assumptions on the signal covariance structure. Comparisons with the National Centers for Environmental Prediction–National Center for Atmospheric Research global atmosphere reanalysis, with the National Center for Atmospheric Research historical analysis of the Northern Hemisphere SLP, and with the global historical analysis of the U.K. Meteorological Office show encouraging skill of the present product and identifies noninclusion of the land data as its main limitation. Marine SLP pressure proxies are produced for the land stations used in the definitions of the Southern Oscillation and North Atlantic Oscillation (NAO) indices. Surprisingly, they prove to be competitive in quality with the land station records. Global singular value decomposition analysis of the SLP fields versus sea surface temperature identified three major patterns of their joint large-scale and long-term variability as ‘‘trend,’’ Pacific decadal oscillation, and NAO.