Impacts of Remotely Generated Internal Tides on the Energetics in Regional Simulations of the California Current System.

Abstract:

In regional high resolution model simulations, frequency-wave number spectra lack energy near the tidal bands when compared to observations. One possibility for this discrepancy could be the lack of remotely generated internal tides in the regional simulations. In this study, we consider the impact of remotely generated internal tides on energetics in regional simulations of the California Current System (CCS). The CCS is an eddy-rich mid-latitude region, where energetic NIWs and internal tidal waves coexist. High resolution realistic regional simulations are carried out using the Regional Ocean Modelling System (ROMS). The ROMS simulations are boundary-forced with offline data from the Hybrid Coordinate Ocean Model (HYCOM). The HYCOM simulations are realistically forced with tides and atmospheric forcing. We consider a year-long HYCOM simulation with a 8-km horizontal grid resolution and 41 layers.

Depth-integrated semidiurnal baroclinic Kinetic Energy in the parent HYCOM domain shows the existence of remotely generated internal tide beams at the location of the ROMS domain. These beams mainly consist of mode 1 and 2 waves. We have interpolated the 3D HYCOM fields onto the ROMS boundaries and performed test simulations to check for spurious waves and currents. We have forced the 4-km ROMS simulations with HYCOM fields consisting of 1) surface and internal tides and mesoscale flows, 2) high frequency surface and internal tides, and 3) surface tides and mesoscale flows. The simulated surface and internal tides in ROMS agree with observations. The ROMS simulation correctly simulates the high-mode internal tides from the Mendocino Escarpment. Moreover, the standing wave with the clockwise depth-integrated flux pattern in the Santa Cruz basin is also simulated.

In the future, we will nest down to high-resolution horizontal ROMS grids. We will diagnose the simulations with the different boundary forcings and study the internal-tide energetics and the energy exchange between the waves and the subinertial flows in detail. These analyses will be done for undecomposed fields and for the fields decomposed into vertical modes.