Assignment - Geostrophy#

Using the thermal wind equation, we can estimate the vertical shear in meridional velocity based on zonal density gradients. However, the method assumes accurate measurements of salinity and an assumed level-of-no-motion. How do these assumptions affect the accuracy of a transport estimate?

Aim: The purpose of this assignment is to evaluate the sensitivity of a geostrophic transport calculation to choices made during the calculation.

Tips and hints:

  1. You have available hydrographic section data and mooring data (see data section below).

  2. Set up code to calculate the geostrophic transport from (i) hydrographic sections and (ii) between moorings. Focus on a narrow region at the western boundary of the Atlantic (e.g., between 77°W and 72°W). You will want to implement a method where you can change the reference level.

  3. Some useful calculations: Take a look at your data sources (use at least one ship-based source and one moored source). What time periods are availble? You will want to run any comparison over the same time period.

  4. You will need a metric or metrics over which to evaluate. Recommended: the transport of the Antilles Current (see Meinen et al. [2019]) or deep western boundary current (see Johns et al. [2008]).

  5. Vary the choice of geostrophic reference level according to choices in the published literature for 26°N region. (See e.g., Bryden et al. [2005] or Atkinson et al. [2012] or Johnson et al. [2008]). Evaluate the effect of your choice on the metric.

Data: Data available include the CTD data from

Note if the files are large (larger than 10 GB) you should not commit them to the repository. To avoid committing you can add the file name to your *.gitignore before committing to your repository.

Directions: Produce a summary report and git repository of your analysis. See Report requirements for formatting details.