Observations of seawater temperature and salinity as the main source of information on large-scale ocean currents

Abstract

A. S. Sarkisyan developed a diagnostic method in the 1960s, based on the inclusion of annual mean temperature and salinity fields in circulation models, which made it possible to simulate climatic currents in the World Ocean and a number of other marine basins. As observations of seawater temperature and salinity accumulated, their climatic seasonal cycle became available on regular grids for several marine areas. Therefore, A. S. Sarkisyan and his followers extended the diagnostic method by proposing a set of algorithms, including nudging, which allowed the simulation of seasonal circulation for any individual marine basin. Recently, the possibility has emerged of using daily eddy-resolving three-dimensional temperature and salinity fields reconstructed from satellite observations on a regular grid. This makes it possible to apply nudging to the reanalysis of the Black Sea state and to off-line field analysis of the World Ocean. Nudging has shown good correspondence with similar results obtained by more complex assimilation schemes. Based on these results and developing the ideas of A. S. Sarkisyan that the key information about ocean currents is contained in the spatial distribution of the density field, an economical algorithm for four-dimensional variational assimilation of temperature and salinity observations in an ocean circulation model is proposed here.