Sea water density parameterization for baltic sea

For modelling of internal waves in the ocean, an important task is to estimate the density stratification in the computational domain for the initialization of the models. In this case, a particular difficulty arises: data from various sources can have different resolutions, be based on different sets of initial measurement results, and have different averaging and smoothing algorithms. In this regard, the purpose of this study is to assess the sea density stratification from hydrology data (GDEM and WOA) from the point of view of the applicability of analytical models. Simplified layered models of stratified fluid are the most attractive for theoretical studies: The number of parameters of the medium is small, and analytical solutions can be constructed quite easily. The simplest layered model is a two-layer fluid. A large number of analytical, numerical, experimental laboratory and field studies have been devoted to the study of internal wave motions, and the properties of waves at the interface in such a model. Physical processes in two-layer fluid have been investigated from all possible aspects in the framework of linear, weakly and fully nonlinear theories. Cases of a multilayered medium are intermediate between a two-layer and continuously stratified, while allowing some analytical results. In the present research zoning of the Baltic Sea by the type of density stratification is carried out. Areas, in which the vertical profile of the sea water density is well approximated by a two-or a three-layer model, are marked out. Such zoning makes possible to simplify the preliminary investigation of internal gravity waves in the region, effectively reducing it to the use of known analytical results for waves propagating at the interface between the layers of constant densities, and it is easy to make preliminary estimates of their kinematic and nonlinear characteristics. Maps of distributions of parameters' values for layered models in winter and summer seasons are given. The seasonal variability of these zones is discussed. Hydrological data for calculating the density field are taken from the GDEM climatology. In addition, we use the calculated temperature and salinity data from the RCO model for the Baltic Sea. Areas with density stratifications close to symmetric with respect to the half-depth are particularly allocated. For such regions, the nonlinear properties of wave processes are subject to further refinement because lower-order nonlinearities vanish in weakly nonlinear models.