A plot of current velocity over a tidal cycle in which each vector starts at the centre and its tip traces an ellipse. The major axis gives the main flow direction and peak speed, the minor axis the cross-flow, and the sense of rotation shows clockwise or anticlockwise turning. A very thin ellipse means a reversing current; a near circle means a strongly rotary one. Each constituent has its own ellipse from harmonic analysis of current data.
M2 current ellipse is long and skinny along the channel axis, 1.6 knots on the major, 0.2 on the minor.
Also heard as
- tidal ellipse
Related terms
Rotary current
An offshore tidal current whose direction keeps swinging round the whole compass during each tidal cycle.
Reversing current
A tidal current that runs back and forth along one line, flood one way and ebb the other, with slack at each change.
ADCP
Acoustic Doppler current profiler: an instrument that measures current speed and direction at many depths at once.
Harmonic analysis
Breaking an observed water level or current record into its tidal constituents to find each one's amplitude and phase.