Purpose. The purpose of the work consists in studying the structure and flow routes of the transformed North Sea waters in the Baltic Sea during the formation and spread of the Major Baltic inflow in December 2014 using numerical modeling.
Methods and Results. To achieve the stated aim, a three-dimensional baroclinic hydrodynamic model of the North and Baltic seas with a spherical grid area detailed in the Danish straits has been developed based on the INMOM model. Within the framework of the performed numerical experiment, the oceanological characteristic fields were assessed in the system of two seas for the period from 1 January 2014 to 31 December 2015. Comparison of the model-derived salinity and sea current characteristic values with those measured at the Darss Sill and Arkona stations as well as with the BSPAF regional reanalysis data has shown that in general, the INMOM model reproduces changes both in salinity and characteristics of the average currents better than the reanalysis data. The features of vertical variability of salinity and sea currents in the Danish straits during the Major Baltic inflow formation are described based on the modeling results. The daily average and total volumes of water transported in the Sound, Great Belt and Little Belt straits during the main period of the Major inflow are estimated. The features of distribution of the near-bottom salinity fields during different periods of its formation are described. The Lagrangian modeling made it possible to describe the ways in which the waters of the Major Baltic inflow spread.
Conclusions. The estimates of water exchange obtained due to the INMOM model indicate that during the main period of the Major Baltic inflow (December 2014), a total of 241.4 km3 of the Kattegat waters passed through the Danish straits. The inflow largest part, 170.9 km3, spread through the Great Belt Strait, while only 68.9 km3 passed through the Sound Strait. The effect of the Small Belt Strait on water transport during the Major Baltic inflow was very insignificant – only 1.6 km3. The study of distribution routes of the transformed North Sea waters over the Baltic Sea after the end of the Major Baltic inflow shows that having passed the Danish straits, its waters spread in a wide flow to the Southwestern Baltic, then penetrate to the Gulf of Gdansk, move further along a cyclonic trajectory through the deep-sea areas of the eastern and northern parts of the Gotland Basin without entering the Gulf of Finland and reach the Landsort Deep in the western part of the Gotland basin by the end of December 2015.