Features of summertime circulation in the Gulf of Riga (A numerical simulation)

Abstract

A regional, 0.5 n.m. and 20 sigma layer grid model of the Gulf of Riga (GoR) was implemented based on the Princeton Ocean Model code with initial conditions and atmospheric forcing taken from HIROMB and HIRLAM output. A basic run that covers an ice-free period of May 1-December 31, 2012, brought the following results: - the mean summertime surface circulation in GoR displays a whole-basin anticyclonic gyre with more intense currents in the western half of the gyre; - two seasonal currents are identified: the Northern Longshore Current (NLC) in the western part of GoR and the Southern Subsurface Longshore Current in the eastern part of GoR; - in the cold season of the year (when seasonal pycnocline is absent), the anticyclonic gyre in GoR is replaced by a cyclonic gyre. The seasonal change in sign of the whole-basin surface circulation in GoR is likely controlled by the NLC, a baroclinic jet-like current formed along the western shore in summer due to the prevalence of southwesterly, upwelling-favored winds, and presence of seasonal stratification that can be approximated as a two-layer vertical structure; this baroclinic jet disappears in winter when the seasonal pycnocline is absent.