This is an essential component of studies of coastal flow patterns, surge tides and astronomical tides. Signals (usually elevation or current meter data) are analysed to give harmonic components and predictions (in the case of current meter data this may take the form of tidal ellipses).
Non tidal signals can then be separated from the raw data. For elevation data these may take the form of surge elevations or river inputs. Lag analysis can be performed to separate phase and elevation effects. For current meter data, residual flows can arise from a variety of sources, e.g. density flows, coastal flows, topographically driven flow, wind driven flow, etc.
Tidal software includes T_tide and Utide, and also in house analysis routines.
Non tidal analysis
Residual flows are usually extracted after suitable tidal analysis and can occur at a large range of frequencies. For example, density flows may have a seasonal character, surges occur over periods of about a day or two, but there are also shorter term flows. Short term flows of periods of the order 1 hr can be caused by wake shedding from islands, seiching, etc. At very short timescales, waves and turbulence may be distinguished in adcp signals, given sufficiently fast sampling times. Structure function and correlation analysis of turbulent signals can be carried out.
Residual flow is important
in dispersion of tracers and pollutants, while non tidal flows (e.g.
island wakes) may form a significant component of the resource at a
tidal site. this case, statistical properties of such flows can be
calculated from models or observations.
Possible work includes:
-tidal analysis of elevation or current data
-calculation of residuals
-relation of residuals to forcing, e.g. wind, river flow, heating, etc.
-extraction of wave and turbulence parameters from adcp data