Eddies

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Eddies#

Detection#

The eddies detection is performed by detect_eddies() with the following procedure:

  1. Find eddy centers with find_eddy_centers() in a velocity field and given a window.

    1. Compute the local normalized angular momentum (LNAM) with get_lnam().

    2. Compute the Okubo-Weiss parameter (OW) with get_okuboweiss().

    3. Mask values of LNAM where the OW is negative.

    4. Find local extrema of LNAM with find_signed_peaks_2d() which define eddy centers.

  2. Loop on eddy centers and initialize an GriddedEddy2D instance from the gridded fields and eddy properties:

    1. Estimate local eddy pseudo-SSH from currents with fit_ssh_from_uv() if not already provided. It is generally useful for subsurface detections. It is possible to directly integrate the stream function based on the velocity field (faster).

    2. Compute SSH closed contours with get_closed_contours() and store them in contours. The search is made in a defined window

    3. Keep the largest contour that defines the eddy boundary and store it in boundary_contour.

    4. Interpolate the velocity onto contours with add_contour_uv, then find the contour with the maximal average speed and store it in vmax_contour.

    5. Check the eddy validity following 4 criteria: existence of at least one closed contour including the center, minimum radius, avoid coastal detection, ellipticity of the velocity contour.

    6. If the velocity contour matches the eddy boundary contour, expand the search to a larger window.

  3. Loop through eddies to avoid double-counting (eddy inclusion). If two eddies share part of the maximum velocity contour, keep only the one with the largest LNAM.

  4. Parameters: The eddy detection is based on three main parameters and an optional fourth one.

    1. window_center: Size of the window for LNAM computation.

    2. window_fit: Size of the window for search of closed SSH contours.

    3. min_radius: Minimum radius size. Note that the radius considered is the one of the maximum speed contour.

    4. ellipse_error (optional):

Tracking#

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