We propose to develop a tomographic observing network for monitoring global ocean changes by tracking long-range propagating internal tides. This technique is called internal tide oceanic tomography…

This federal contract award to the University of Washington (UW) was issued by the National Aeronautics and Space Administration (NASA) Shared Services Center to develop a tomographic observing network for monitoring global ocean changes by tracking long-range propagating internal tides. The technique, called Internal Tide Oceanic Tomography (ITOT), uses satellite altimetry data to measure changes in ocean heat content and associated steric height along internal tidal beams globally. The $319,282.12 grant will support quantifying uncertainties, evaluating the approach using the ECCO2 state estimate, and calibrating the results against Argo measurements. This effort is expected to increase long-term observational capabilities and contribute to climate research programs. The contract does not have a set-aside designation.

We propose to develop a tomographic observing network for monitoring global ocean changes by tracking long-range propagating internal tides. This technique is called internal tide oceanic tomography (itot), in analogy to acoustic tomography brought up by munk and worcester (1976) 40 years ago. Itot is similar to acoustic tomography, but that the working waves are internal tides instead of sound. The underlying principle is that upper-ocean temperature changes strengthen/weaken ocean stratification and thus increase/decrease the internal tide s propagation speed, therefore ocean warming/cooling can be monitored by precisely measuring travel time changes of internal tides. This technique is inspired by our recent advances in observing internal tides from satellite altimetry. Itot offers a long-term, low-cost, environmentally-friendly observing network of global ocean changes. By itot, we can measure changes in ocean heat content (OHC) and associated steric height (SH) along internal tidal beams globally, complementing in situ observing programs (argo, XBT, go-ship, etc.). The feasibility and usefulness of this technique are demonstrated in our preliminary results. In the proposed research, we will develop this technique by quantifying its uncertainties, evaluating IT using the ECCO2 state estimate, and calibrating its results against argo measurements. (1) we will examine the accuracy of the phase of internal tides derived from satellite altimeter data. We will compare the phase change rates of overlapping internal tidal beams and of four tidal constituents (M2, S2, O1, and K1). Our goal is to reduce the uncertainties caused by empirical parameters used in our mapping method. (2) we will construct the conversion function from the internal tide s speed changes to OHC changes. Its uncertainties will be quantified using argo-measured and ideal warming profiles (e.g., with abyssal warming). (3) we will investigate the seasonal variations of the internal tide s speed and argo-measured OHC. Our preliminary analysis reveals that the seasonal cycle is a strong function of location. (4) both stratification (thus the internal tide s speed) and OHC changes can be directly computed from the ECCO2 state estimate. Thus we can evaluate itot using the ECCO2 estimate and assess effects of salinity and currents. (5) we will calibrate the itot-derived OHC and SH results against argo measurements in 2005 2014. After calibration, we will present a 20-year-long product, doubling the ~10-year-long argo time series. Our understanding of global climate variability and change is mainly hampered by inadequate observational data. IT is thus of high priority to develop new observing techniques. Itot based on satellite altimetry provides a great opportunity to monitor global OHC changes from space. This technique will surely increase our long-term observational capability and contribute significantly to the world climate research program s clivar project.