It is important to understand the generation and propagation of near-inertial internal waves, which are thought to contribute to deep-ocean mixing and maintenance of the abyssal stratification. Mesoscale eddies and currents affect the subsurface pathways of near-inertial waves from the mixed layer to the sea floor, and may deflect, trap, and focus them. Recent numerical models support these predictions, but much work remains to understand and verify how near inertial waves propagate to redistribute their energy in and under strong current systems. Due to the intense air-sea interactions in the Kuroshio Extension, ocean variability can potentially affect the winds and climate in remote regions. In particular, the subtropical mode water (STMW) has been considered as a large upper-ocean heat reservoir closely linked to the climate system. The non-uniform cooling and deepening of the surface mixed layer forms the STMW during winter with high variability in space and time.
This project will investigate the upper and deep ocean response to atmospheric forcing in the Kuroshio region using oceanic and atmospheric observations collected as part of the Kuroshio Extension System Study (KESS) and the Kuroshio Extension Observatory (KEO) programs. The project will focus on the generation of near-inertial motions from the wind, how and where they propagate and dissipate, and how they directly affect the mass and heat budget of the mixed layer and STMW. The KESS array, deployed during May 2004?June 2006, comprised subsurface moorings with moored profilers and current meters, and inverted echo sounders equipped with near-bottom pressure and current sensors. KEO, a moored surface buoy, was first deployed in 2004 as part of KESS and is now part of the sustained ocean climate observing system. The KESS array is uniquely suited to conduct these studies due to its combination of vertical, horizontal, and temporal resolution and extent of spatial coverage.
Understanding gained from this project has broad applicability in testing parameterizations of mixing in climate models and theoretical concepts of how near-inertial waves can be carried, trapped, and concentrated by strong current systems. The processes and feedbacks related to mode water formation by air-sea interaction are likely to be important in regions where strong winds blow over an ocean full of fronts and mesoscale eddies such as around the Southern Ocean. These processes are of great importance for climate variability, the focus of the Climate Variability and Prediction (CLIVAR) program. KESS has been included in CLIVAR from its planning phase and its findings complement other U.S. CLIVAR studies (e.g., CLIMODE, SAMFLOC, and DIMES). As global ocean models and wind fields achieve increasingly high resolution, allowing direct simulation of near-inertial waves, it will be important to have documented examples of the oceanic response in particular of the near-inertial waves in a strong mesoscale flow field to episodic atmospheric forcing.
