Skip to content. | Skip to navigation

Laboratoire d’Etudes en Géophysique et Océanographie Spatiales

Personal tools

This is SunRain Plone Theme

Navigation

You are here: Home / Events / Seminars / Seminaires Septembre 2018-Aout 2019 / Jeudi 20 Juin - Internal tides and Indonesian Seas

Jeudi 20 Juin - Internal tides and Indonesian Seas

by SEMSOU last modified Jun 26, 2019 09:18 AM
When Jun 20, 2019
from 10:00 AM to 11:00 AM
Where salle Clairaut
Add event to calendar vCal
iCal



Océane Richet

CSIRO (Commonwealth Scientific and Industrial Research Organisation), Hobart

 

Title: Internal tides and Indonesian Seas

 

Abstract : I will talk about to different studies. The first topic is about the mechanisms leading to the dissipation of internal tides at the topography. The second topic is the study of the impact of the seasonal variability on the background state of the Indonesian Seas. 

-- Several studies have shown the existence of a critical latitude where the dissipation of internal tides is strongly enhanced. Internal tides are internal waves generated by barotropic tidal currents impinging rough topography at the seafloor. Their dissipation and concomitant diapycnal mixing are believed to be important for water masses and the large-scale ocean circulation. The purpose of this study is to clarify the physical processes at the origin of this strong latitudinal dependence of tidal energy dissipation. We find that different mechanisms are involved equatorward and poleward of the critical latitude. Triadic resonant instabilities are responsible for the dissipation of internal tides equatorward of the critical latitude. In particular, a dominant triad involving the primary internal tide and near-inertial waves is key. At the critical latitude, the peak of energy dissipation is explained by both increased instability growth rates, and smaller scales of secondary waves thus more prone to break and dissipate their energy. Surprisingly, poleward of the critical latitude, the generation of evanescent waves appears to be crucial. Triadic instabilities have been widely studied, but the transfer of energy to evanescent waves has received comparatively little attention. Our work suggests that the nonlinear transfer of energy from the internal tide to evanescent waves (corresponding to the 2f-pump mechanism described by Young et al., 2008, https://doi.org/10.1017/ S0022112008001742) is an efficient mechanism to dissipate internal tide energy near and poleward of the critical latitude. The theoretical results are confirmed in idealized high-resolution numerical simulations of a barotropic M2 tide impinging sinusoidal topography in a linearly stratified fluid. 

-- The Indonesian Seas at short time scales (14 days) control the weather regionally through air-sea exchanges and its role in the development of deep atmospheric convection and at the longer climate time scale by providing the only link between the tropical Pacific and Indian Oceans. In between those time scales, we know that the seasonal cycle is large over the region, but we do not know how it contributes to the background state, which feeds both back into the weather and the climate. This study investigates the response of the background state of the Indonesian Seas to seasonally variable forcing using a high-resolution regional model. Our model results suggest that the signal induced by the seasonality of the forcing is confined in the surface layer. The seasonality of the forcing, especially the one of the monsoonal winds, induces a deepening of the mixed layer depth in the Indonesian Seas due to Ekman pumping and mixing at the base of the mixed layer with water below, leading to colder surface water. The observed changes on the background SST induced by the seasonal variability of the forcing in our simulations have the same order of magnitude than the seasonal cycle of the SST itself. Understanding the mechanisms behind the SST and SSS is essential to predict the response of the ocean to changes in the forcing.


Le lien de la présentation est disponible ici

Document Actions

Navigation