## Constituent ellipse

### From BAWiki

Harmonic constituents of two dimensional vectors are described by the parameters of an ellipse as displayed in the figure. The vector of the constituent follows the dark blue trajectory. The meanings of the parameters are:

- U : the major semiaxis of the ellipse. This is the maximum value of the constituent vector.
- u : the minor semiaxis of the ellipse. This is the minimum value of the constituent vector. Negative values indicate a clockwise rotating constituent vector, positive values a counterclockwise rotating one.
- g : the local phase angle in relation to the forcing (here represented by the yellow moon). It is calculated with respect to 01\01\ of the actual year, 0:00 UTC. It is analog to the local phase of an analysed scalar property.
- theta: the direction of the main axis, here related to the geographical northing.

Documentation/Literature:

**Foreman M.G.G. - Manual for Tidal Currents Analysis and Prediction** Institute of Ocean Sciences, Patricia Bay, Sidney, British Columbia, **1979-1996**

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