Mixing in the Indonesian Throughflow: Analysis of Lagrangian observations of shear, watermass modification, and internal wave climates

University Of Washington, Seattle WA

Investigators

Abstract

Recent computer simulations have suggested the appearance of tides at the interfaces between different layers (internal tides) in the basins and straits of the Indonesian and Philippine Archipelagos (the Coral Triangle), with subsequent mixing of the layers. These tides carry and transform waters from the Pacific on their path to the Indian Ocean. Despite the computer-generated results, direct measurements of internal tides and mixing have been scarce in this region. This project will use Lagrangian (i.e., following the horizontal flow pathway) measurements of temperature, salinity, and currents from vertically profiling floats to investigate the levels of internal waves, especially internal tides, and their role in transforming water properties through vertical mixing. The project will use existing data from the Philippines Archipelago, along with additional new float deployments in the separately funded (NSF) "Measuring and Modeling the INdonesian Throughflow International Experiment" (MINTIE). Results will be used to evaluate the internal tide and circulation characteristics of computer models being used in the region. The project will support an international (US–Australia) collaboration and facilitate the broader use of electromagnetic velocity profiler data by providing raw profiles and derived internal wave and mixing products through national data centers. The project will furnish project material for undergraduate interns in a new APL-UW program targeting minorities. Mixing along the Pacific-to-Indian Ocean throughflow pathway is a key water mass transformation step in the global thermohaline circulation and has a first-order influence on sea-surface temperature and air–sea interaction. The locations of predicted internal tide generation are very likely to be mixing hot spots, but it remains an open question where and how the radiated internal tide energy is dissipated. This proposal will test the dominance of internal tides as mixing agents. The results will be used to evaluate the internal tide and circulation characteristics of numerical models being used to test throughflow sensitivity to the level and distribution of mixing in the region. Project's goals include: 1) the description of internal tide amplitude and radiation patterns in both the Philippine and Indonesian Seas to verify sources, diurnal and semidiurnal contributions (including the spring/neap cycle of each), and vertical wavenumber structure; 2) constraining the parameters appropriate to internal tide parameterizations, especially the fraction of energy radiated and the vertical structure of the resulting dissipation; 3) evaluation of along-path water mass transformation rates; 4) establishing a shared and publicly available database for EM-APEX profiles, of use for research studies like this one and ocean state and forecast systems assimilating stratification and velocity data. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.