Connectivity between intraseasonal oscillations, equatorial ocean jets, and ocean stratification in the western Indian Ocean
Abstract
The western Indian Ocean is increasingly recognized as a region of importance for strong air-sea coupling, including the initiationof Madden-Julian oscillation (MJO) and other intraseasonal oscillations (ISOs). The upper ocean stratification in the western Indian Ocean makes the region susceptible to these significant air#sea interactions. Subsequently, several previous studies have recognized the accurate characterization and simulation of the upper ocean stratification as an essential process towards the accurate reproduction of ISOs. Upper ocean stratification is primarily controlled by the competing influence of temperature and salinity, with factors that influence the variability of salinity (e.g., precipitation, evaporation, and currents) at different timescales (e.g., intraseasonal, seasonal and interannual) potentially impacting the occurrence, spatial and temporal dynamics of upper ocean stratification. The barrier layer thickness, a proxy used to quantify the degree of upper ocean stratification, can be generated locally or remotely. A potential source of upper ocean stratification in the western Indian Ocean is intraseasonal westward equatorial jets which advect low saline waters and/or barrier layers from the eastern basin and equatorial regions of the Indian Ocean. This mechanism for the generation of stratification in the western Indian Ocean has been less explored in the literature, thus underestimating the contribution of upper ocean stratification to the structure and propagation of ISOs. The characteristics, seasonality and mechanismsfor the formation of the barrier layer in the western Indian Ocean are explored in this study. Intraseasonal variability of ocean currents is generated by resonant winds. Low-level winds associated with the ISOs accelerate surface zonal currents in the equatorial Indian Ocean. We hypothesize that the intraseasonal westward jets will advect low salinity waters and barrier layer from the east toward the equatorial and western Indian Ocean. This low salinity waters and barrier layer from the east will subsequently cause or deepen stratification in the west. The stratification traps momentum, heat and freshwater fluxes which feeds back to, generate orstrengthen ISOs, thereby resetting the cycle. This study will use satellite and in-situ observations and the HYbrid Coordinate Ocean Model (HYCOM) to characterize the occurrence, evolution, features and intraseasonal variability of westward surface jets in the equatorial Indian Ocean, its influence on upper ocean stratification and connection with ISOs in the western Indian Ocean.Future NavalRelevance Temperature and salinity influence the density and sound speed in multiple ways. For Naval applications, upper ocean stratification, circulation, understanding fresh and saltwater transports, mixed layer and barrier layer dynamics in the western Indian Ocean is relevant in the area of anti-submarine warfare. Salinity variability impacts sonic depth, density fronts and the depth of both the mixed layer and thermocline, which are important for acoustic performance predictions.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Nov 09, 2024
- Source ID
- N000142412690
Entities
People
- Ebenezer S. Nyadjro
Organizations
- Mississippi State University
- Office of Naval Research
- United States Navy