| Popis: |
The Southeast Tropical Indian Ocean region has a complex background current system whose instabilities lead to eddy generation through energy cascade. Many studies have documented the eddy activity in the region. More recently the generation of these features were investigated, being ocean shear velocity and tropical Pacific winds identified as important forcings of these westward-southwestward propagating features. By mixing and advecting anomalous waters, eddies not only have act on fertilizing the ocean surface layer but also have effect on the properties of the mixed layer. As a consequence, eddy activity may have a significant impact on the ocean-atmospheric fluxes of this highly dynamic region. Here we present a case study focused on a 2.5 months high temporal and vertical resolution data from 2 gliders deployed between Christmas Island and Java Island, in which we explore the temporal evolution and the effects of eddy advection and atmospheric forcing on the ML properties. Spatial information was complemented by using the Nemo global analysis forecast product (1/12 degree). Nemo forecast of changes in the average temperature, salinity and depth of the mixed layer caused by the advection of eddies closely fits the glider data close to Java and the Sunda and Lombok Straits. It’s capability decays as we move away from the coast, a main source of the eddies, as the mesoscale features acquire a more filament nature, and thus becoming more challenging of closely reproduction. Nevertheless, Nemo constituted as a useful tool for defining the oceanic basic state previous to the deployment and estimate horizontal shear and eddy advection time. Nemo and glider data showed the expected thermodynamical response associated with intraseasonal atmospheric systems, such as the decrease/increase in SST during active/suppressed phases of MJO, Convectively coupled Kelvin waves and Equatorial Kelvin waves observed during the deployment and identified in filtered GPM precipitation and ERA5 wind data. Besides the atmospheric forcing, eddy activity also varied throughout the mission, as well as the role of temperature and salinity in setting the mixed layer depth. We identified initially that the effect of eddy advection on SST can differ depending on the presence or intensity of the atmospheric forcing. As future work, we intend to combine this environmental information with Nemo and the high vertical resolution data from the glider to explore the role of eddy advection, ocean background state and atmospheric forcing on setting the ML properties during the glider deployment and the effect of the ocean-atmospheric fluxes. |
