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Ocean Surface Topography from Space
Mining sea surface height to improve understanding and predictability of mid-latitude air-sea interaction


LuAnne Thompson - (University Of Washington, Seattle)

Co-Investigator/Science PI:
  Dr. Kyla Drushka
(University Of Washington, Seattle)

Over two decades of continuous satellite altimetric sea-surface height (SSH) data has allowed advances in understanding how the ocean stores and transports heat on intra-seasonal to interannual times scales. In tropical air-sea interaction studies, SSH has been used to improve forecasts of hurricanes, but SSH has not been used to its full potential in mid-latitude air-sea interaction studies. The proposed work aims to determine where and when SSH could be used to improve predictability of mid-latitude air-sea interaction on seasonal to interannual times scales.

In mid-latitudes, coupling between the atmosphere and the ocean is typically examined using sea surface temperature (SST) as a metric for ocean state. SST is strongly linked to upper ocean heat content in winter. However, in summer, SST is decoupled from the ocean’s seasonal thermocline, where the temperature from the previous winter is sequestered. Since SSH is strongly linked to depth-integrated temperature (heat content) anomalies through thermosteric expansion, it retains information about subsurface temperature anomalies even in the summer. This attribute gives SSH a longer memory than SST, and the use of SSH as a proxy for heat content increases the potential for predictability of air-sea interaction.

The proposed work includes a detailed evaluation of the use of SSH (as a proxy for upper ocean heat content) in air-sea interaction studies on regional scales in each of the mid-latitude ocean basins with a focus on the western boundary current separations and their termination regions. Ocean interiors, where currents are generally small, will also be examined for comparison. The analysis will use the full altimetric SSH record, several in situ Argo-based ocean products including temperature and salinity profiles and mixed-layer depth compilations, satellite-derived sea surface temperature (SST), ocean mass from GRACE, and latent and sensible heat fluxes. In addition, a recent 100-year simulation of a high-resolution ocean-atmosphere coupled model from the National Center from Atmospheric Research will be used to help to constrain the relationship between SSH and heat content. The model has a nominal ocean resolution of 10 km, allowing robust simulation of western boundary current dynamics and their variability. In addition, the coupled model has a closed heat budget by construction, so sampling and measurement errors can be ignored when examining modeled air-sea interaction.

The specific objectives of this project will be to analyze a suite of satellite and in situ observation along with the coupled climate model to:

  1. refine the relationship between SSH and heat content in mid-latitudes;
  2. quantify the drivers of upper ocean heat content anomalies;
  3. evaluate the relative strength and time scales of linked variability between SSH and SST and surface turbulent heat fluxes;
  4. improve predictability of air-sea heat exchanges by linking locations of ocean forced heat exchange to low frequency variability of strong western boundary currents, their extensions, and their terminations.

This work supports NASA objectives to use the 20-year altimetry record, in combination with other data and models, to understand the large-scale redistribution of ocean heat and its relationship to exchanges with the atmosphere. This research also supports NASA's research priority to understand how climate variations induce changes in global ocean circulation, and in turn how those variations in ocean circulation can impact climate.

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