An Increase of the Indonesian Throughflow by Internal Tidal Mixing in a High‐Resolution Quasi‐Global Ocean Simulation

Abstract

The impact of internal tidal mixing on the volume transport of the Indonesian Throughflow (ITF) is examined by a comparison of high‐resolution quasi‐global ocean simulations with and without a tidal mixing scheme. The ITF transport is found to be increased in the presence of tidal mixing. This is because tidal mixing decreases the density within and below the lower thermocline and increases the buoyancy of the water column. As a result, the surface pressure and the sea surface height (SSH) are raised. The magnitude of the SSH increase is larger for the tropical Pacific Ocean than for the other basins, possibly because many islands exist in the tropical Pacific and tidal mixing is effective around their shallow and rough topographies. Since SSH increases more in the tropical Pacific than in the Indian Ocean, the pressure difference between the two basins is enhanced and thus the ITF transport is strengthened.

A global eddying hindcast ocean simulation with OFES2

“…6d), the fresher bias (< -0.2 psu) spreads from the western Pacific into the Celebes Sea, gradually weakens southward, and disappears at the Makassar Strait. The saltier bias (> 0.3 psu) spreads to the south of Java and the Sunda Islands, which decreases to approximately 0.2 psu along approximately 12° S. The cause of these biases may be partially due to the lack of nonlocal tidal mixing (e.g., Nagai et al, 2017), as discussed in a study by Sasaki et al (2018). The impact of nonlocal tidal mixing is an interesting subject for a future study.…”

“…Sensitivity experiments are becoming more feasible. Sasaki et al (2018) showed that the inclusion of a tidal mixing scheme can result in an enhancement in ITF transport due to the basin-scale SSH increase in the tropical Pacific Ocean. While the direct impact of tidal mixing is local, its impact appears to spread over a whole basin via Rossby and Kelvin waves (Furue et al 2015).…”

The Fate of Surface Freshwater Entering the Indonesian Seas

“…OFES2 is a quasi‐global general circulation model that has a spatial resolution of 0.1° and is an update of OFES (Masumoto et al, ; Sasaki et al, ), which now includes a global tidal mixing parameterization. Readers are referred to Sasaki et al () for model details. The 22‐year monthly averaged OFES2 outputs are used to estimate the monthly climatologies, which are then used for the analysis unless noted otherwise.…”

“…In order to estimate the trajectories of the Lagrangian particle tracking model, we use OFES2 from 1995 to 2016 (Sasaki et al, 2018). OFES2 is a quasi-global general circulation model that has a spatial resolution of 0.1°and is an update of OFES (Masumoto et al, 2004;Sasaki et al, 2008), which now includes a (Boyer et al, 2013), and red lines are from OFES2.…”

“…Journal of Geophysical Research: Oceans global tidal mixing parameterization. Readers are referred to Sasaki et al (2018) for model details. The 22year monthly averaged OFES2 outputs are used to estimate the monthly climatologies, which are then used for the analysis unless noted otherwise.…”