Collaborative Research: Mapping the kinematics and dynamics of tidal ocean currents with surface drifters

点击翻译按钮获取中文摘要

This project is concerned with quantifying and mapping diurnal and semi-diurnal baroclinic tides, that is, internal waves in the ocean that are the result of the loss of energy from the barotropic tides forced by the Sun and the Moon. This work will primarily use a unique dataset of oceanic near-surface hourly currents provided by the trajectories of surface drifting buoys from the Global Drifter Program (GDP). The approach is guided by an analysis of tidal energetics which distinguishes between time-mean, or phase-locked, baroclinic tides and time-variable, or non-phase-locked, baroclinic tides. The GDP dataset is both large enough and sufficiently accurate that it should permit quantitative assessment of both types of baroclinic tides, and specifically test theoretical models for the scattering of phase-locked tides into non-phase-locked tides. In addition, the analyses will permit the mapping---for both phase-locked and non-phase-locked tides---of dissipation rate coefficients and their associated dynamical processes, which can be distinct based on geographical locations and environmental conditions. Such mapping will provide much needed information for improving the realism and physical parameterization of tidal mixing in ocean general circulation models. The work will contribute to the goal of measuring on a global scale upper-ocean currents which ubiquitously exhibit energetic oscillations at tidal frequencies. Improved prediction of ocean surface currents will have societal impacts for stakeholders ranging from the shipping industry to seasonal climate forecasters. The project will also contribute to a climate-themed educational program including summer camps, hands-n activites, and enhancements to existing school field trip programs.Estimates of the phase-locked tides are presently available from the analysis of satellite altimeter data,and these estimates have led to the creation of baroclinic tide models, which this project will test and extend using the GDP data. As tidal dynamics includes both wave scattering and wave dissipation, testing these models will place constraints on the range of physically plausible parameterizations for these processes on regional and global scales. Finally, the GDP data shall be systematically compared with outputs of a tide and mesoscale-resolving ocean global circulation model, an exercise which will be useful for validating the model simulations as well as providing a useful context for understanding potential biases of the GDP observations and statistical methods applied. This project will generate new knowledge concerning tidal currents in order to better understand tidal dynamics and their role in the maintenance of the global thermohaline ocean circulation. The new drifter dataset that will be utilized to investigate baroclinic tidal phenomena is both large enough and unique (temporally, spatially and accuracy wise) to provide a quantitative description of tidal properties. In addition, qualitative and potentially new assessments of tidal/non-tidal interactions will be obtained, including their seasonal and longer temporal variability. A novel decomposition of the tidal energy budget, which separates processes primarily affecting phase-locked and non-phase-locked tidal signals, is proposed to guide the analysis and interpretation of the drifter observations, as well as altimetry data and numerical simulations.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.