Eddy‐topography interactions and the fate of the Persian Gulf Outflow

Abstract

The Persian Gulf feeds a warm and salty outflow in the Gulf of Oman (northern Arabian Sea). The salt climatological distribution is relatively smooth in the Gulf of Oman, and the signature of a slope current carrying salty waters is difficult to distinguish hundreds of kilometers past the Strait of Hormuz, in contrast to other outflows of the world ocean. This study focuses on the mechanisms involved in the spreading of Persian Gulf Water (PGW) in the Gulf of Oman, using a regional primitive equation numerical simulation. The authors show that the dispersion of PGW occurs through a regime that is distinct from, for example, the one responsible for the Mediterranean outflow dispersion. The background mesoscale eddy field is energetic and participates actively to the spreading of PGW. Remotely formed eddies propagate into the Gulf of Oman and interact with the topography, leading to submesoscales formation and PGW shedding. Eddy‐topography interactions are isolated in idealized simulations and reveal the formation of intense frictional boundary layers, generating submesoscale coherent vortices (SCVs). Interactions take place at depths encompassing the PGW depth, thus SCVs trap PGW and contribute to its redistribution from the boundaries to the interior of the Gulf of Oman. The overall efficiency of these processes is confirmed by a strong contribution of eddy salt fluxes in the interior of the basin, and is quantified using particle statistics. It is found to be a highly dispersive regime, with an approximated eddy diffusivity of ∼1700 normalm2 normals−1.

Western boundary upwelling dynamics off Oman

“…Notice that the annual EKE over the whole domain is higher in ROMS than in Aviso by ∼ 20% (Fig. 3 in Vic et al 2015).…”

“…Bottom stress is linear with a drag coefficient C d = 3 × 10 −4 m s −1 . Additional information is in Vic et al (2015).…”

Scales and dynamics of Submesoscale Coherent Vortices formed by deep convection in the northwestern Mediterranean Sea

“…Other generation mechanisms exist for anticyclonic SCVs like the instability of a coastal undercurrent [D'Asaro, 1988b;Molemaker et al, 2015] or the interaction of large-scale eddies with the topography [Vic et al, 2015]. In the NW Mediterranean Sea, the first mechanism has been identified to be important along the northwestern part of Sardinia leading to the formation of ''Suddies'' characterized by warm and salty LIW .…”

Mesoscale eddies and submesoscale structures of Persian Gulf Water off the Omani coast in spring 2011

“…In June 2011, anticyclone A3 was advected northward as the summer monsoon began, thus reducing the deformation field off Ra's Al Hamra. To break the PGW outflow into lenses and filaments, Vic et al (2015), using a highresolution numerical model, showed that a strong shear and strain is necessary. Thus fewer submesoscale PGW structures are expected to be observed during the summer monsoon (when the deformation field is less intense), but due to a lack of regular observations at the depth of PGW.…”