Mesoscale dynamics in the Arabian Sea and a focus on the Great Whirl life cycle: A numerical investigation using ROMS

Abstract

The Great Whirl (GW) is a persistent anticyclonic mesoscale eddy that is observed seasonally in the Arabian Sea during a period embedding the 3 months of the southwest monsoon (June-July-August) at a quasi-steady location. Its dynamics remain unclear despite it being one of the largest coherent vortices in the world ocean. Realistic regional numerical experiments using ROMS are performed to investigate the life cycle of the GW, which is not well resolved by sparse available in situ measurements in the region. Using a set of sensitivity experiments and an accurate temporal characterization of the eddy properties (including position, radius, depth, and vorticity) we (i) confirm the role of basin-scale downwelling Rossby waves in the GW generation, (ii) clarify the role of the monsoonal strong anticyclonic wind in its maintenance and barotropization, and (iii) suggest a connection between basin-scale Rossby wave dynamics and GW collapse.

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

“…In 2011, the wind stress curl off Ra's Al Hadd changed sign from March to May. During this period, the wind work leads to a deepening of the surface eddies (see L'Hégaret et al, 2015 andVic et al, 2014). In Fig.…”

Western boundary upwelling dynamics off Oman

“…2005) set up in a one-way, nested configuration, consisting of two regions: an inner region offshore from Oman with a 2-km horizontal resolution; and an outer ("parent") region with a 6.6-km resolution, which supplies boundary conditions for the inner region (procedure follows Mason et al 2010). The parent simulation is extensively described in Vic et al (2014). The inner domain and topography are shown in the right panel in Fig.…”

“…Currents in ROMS have also been filtered to compute EKE Omani coast (e.g., Fig. 1c in Vic et al 2014). Thus, both τ a and ∇ × τ provide upwelling-favorable forcing during the summer monsoon .…”

Interactions between the Somali Current eddies during the summer monsoon: insights from a numerical study

“…These global simulations were not initially designed to be sensitivity studies of the Arabian Sea to various processes or parameters -as were the regional simulations of Vic et al (2014) for example -and are not suited to be used for such purpose. The use of several simulations rather than a single one is motivated by the fact that the solutions provided by present state-of-the-art eddy-resolving OGCMs still show some dependency on parameter choices and are subject to a chaotic behaviour specific to turbulent flows (Serazin et al, 2015).…”

“…A third anticyclonic eddy named the Socotra Eddy (SE) is reported to be frequently present to the east of the Island of Socotra. The regional numerical model study of Vic et al (2014) of the Arabian Sea points out the importance of the regional wind stress curl in the growth and maintenance of the GW, and the influence of basin-scale Rossby waves in its generation and its interannual variability.…”