It can be used to quantify whether a site experiences
(Figure 4) the following: two high and low tides each lunar
day, semidiurnal tidal form (F < 0.25); a single high and
low tide, diurnal tidal form (F > 3); or periods when
both types occur, mixed tidal form (mixed, mainly
semidiurnal, F ¼ 0.25 to 1.50; mixed, mainly diurnal,
F ¼ 1.50 to 3.00).
Summary
To fully understand tides and predict them, one must understand both the astronomical forcing that gives rise to them
and also the response of the oceans, bays, and estuaries to
this forcing (Parker, 2005). Knowledge of the astronomical
forcing helps to describe several features of tides and
servers as a basis for the tide’s predictability. However, it
is the knowledge of the hydrodynamics of the tide in
a particular ocean basin, shelf sea, or estuary which provides understanding of the timing of high and low water,
the size of the tidal range, the form of the tide, and any complex shallow water distortions of the tidal curve.
Bibliography
Brown, J., Colling, A., Park, D., Philips, J., Rothery, J., and Wright,
J., 1989. In Bearman, G. (ed.), Tides. Waves, Tides and ShallowWater Processes. Oxford: Butterworth Heinemann and Open
University.
Cartwright, D. E., 1999. Tides, a Scientific History. Cambridge:
University Press.
Cartwright, D. E., and Tayler, R. J., 1971. New computations of the
tide-generating potential. Geophysical Journal of the Royal
Astronomical Society, 23(1), 45–73.
Doodson, A. T., 1921. The harmonic development of the tidegenerating potential. Proceedings of the Royal Society of London
Series A, 100(704), 305–329.
Egbert, G. D., and Erofeeva, S., 2002. Efficient inverse modeling of
barotropic ocean tides. Journal of Atmospheric and Oceanic
Technology, 19(2), 183–204.
Foreman, M. G. G., 1977. Manual for Tidal Heights Analysis and
Prediction. Pacific Marine Science Report No. 77–10, Institute
of Ocean Sciences, Patricia Bay, Sidney, BC. http://www.omg.
unb.ca/GGE/5013_LABS/heights.pdf.
Haigh, I. D., Eliot, M., and Pattiaratchi, C., 2011. Modeling global
influences of the 18.6-year nodal cycle and quasi-4.4 year cycle
on high tidal levels. Journal of Geophysical Research-Oceans,
116, C06025, doi:10.1029/2010JC006645.
Masselink, G., Hughes, M., and Knight, J., 2003. Introduction to
Coastal Processes and Geomorphology. London: Hodder Education.
Munk, W. H., and Cartwright, D. E., 1966. Tidal spectroscopy and
prediction. Philosophical Transactions of the Royal Society of
London, A259, 533–581.
Parker, B., 2005. Tides. In Schwartz, M. L. (ed.), Encyclopedia of
Coast Science. Dordrecht: Springer.
Pugh, D. T., 1987. Tides, Surges and Mean Sea Level: A Handbook
for Engineers and Scientists. Chichester: Wiley.
Pugh, D. T., 2004. Changing Sea Levels: Effects of Tides, Weather
and Climate. Cambridge: Cambridge University Press.
Cross-references
Seiche
Storm Surges
Tidal and Nontidal Oscillations
Tidal Asymmetry
Tidal Datum
Tidal Hydrodynamics
Tidal Ranges
TIMESCALE
Lisa V. Lucas
United States Geological Survey, Menlo Park, CA, USA
Definition
Time scale refers to “the time allowed for or taken by
a process or sequence of events” (OUP, 2013).
Essential concepts, application and usage
The above definition provides a general description of the
term “time scale.” In science and engineering practice, a
time scale is typically an estimate expressing a representative, overall magnitude as opposed to a precise value; as
such, time scales (like length, velocity, and other commonly
used scales) are frequently quantified in terms of orders of
magnitude (Cushman-Roisin and Beckers, 2011). A time
scale carries the dimension of time and may be expressed
either in precise temporal units (e.g., seconds, hours, days,
years, decades) or in approximate temporal units (as with
“tidal,” “seasonal,” or “episodic” time scales).
In combination with other scales, time scales may be
used to estimate the relative magnitude (and thus, importance) of individual terms in time-marching equations
(Cushman-Roisin and Beckers, 2011). Time scales may
be defined to describe the rates of physical, biological,
and chemical processes, serving as a common currency
with which to compare their relative speed, and thus
importance (e.g., Koseff et al., 1993; Middleburg and
Nieuwenhuize, 2000; Lucas et al., 2009; Dame, 2012).
In such a context, a smaller time scale suggests a faster
and more dominant process (Lucas, 2010). A time scale
may be estimated as the reciprocal of a first order rate constant or frequency, or from a combination of length, velocity, diffusivity, or other scales such that the remaining
dimension is time (e.g., Fischer et al., 1979; Koseff et al.,
1993). A time scale may reflect the approximate time for
completion of a process, such as for (1) diffusive mixing
over an estuary’s depth (Fischer et al., 1979), (2) advective
transport over the estuary length (MacCready and Banas,
2011), (3) flushing of an estuary by river flow and/or tides
(Sheldon and Alber, 2006), (4) settling of particles through
a water column (de Brauwere and Deleersnijder, 2010),
(5) biomass growth by a factor e (Lucas, 2010), or (6) filtration of a water column or estuary volume by benthic
organisms (Buzzelli et al., 2013).
The term “time scale” may also be used to convey (1) a
typical period of variability or fluctuation in estuarine forcing or ecosystem response (e.g., Litaker et al., 1993; Cloern,
1996; Jay et al., 2000), (2) a period of estuary adjustment to
712
TIMESCALE
(Figure 4) the following: two high and low tides each lunar
day, semidiurnal tidal form (F < 0.25); a single high and
low tide, diurnal tidal form (F > 3); or periods when
both types occur, mixed tidal form (mixed, mainly
semidiurnal, F ¼ 0.25 to 1.50; mixed, mainly diurnal,
F ¼ 1.50 to 3.00).
Summary
To fully understand tides and predict them, one must understand both the astronomical forcing that gives rise to them
and also the response of the oceans, bays, and estuaries to
this forcing (Parker, 2005). Knowledge of the astronomical
forcing helps to describe several features of tides and
servers as a basis for the tide’s predictability. However, it
is the knowledge of the hydrodynamics of the tide in
a particular ocean basin, shelf sea, or estuary which provides understanding of the timing of high and low water,
the size of the tidal range, the form of the tide, and any complex shallow water distortions of the tidal curve.
Bibliography
Brown, J., Colling, A., Park, D., Philips, J., Rothery, J., and Wright,
J., 1989. In Bearman, G. (ed.), Tides. Waves, Tides and ShallowWater Processes. Oxford: Butterworth Heinemann and Open
University.
Cartwright, D. E., 1999. Tides, a Scientific History. Cambridge:
University Press.
Cartwright, D. E., and Tayler, R. J., 1971. New computations of the
tide-generating potential. Geophysical Journal of the Royal
Astronomical Society, 23(1), 45–73.
Doodson, A. T., 1921. The harmonic development of the tidegenerating potential. Proceedings of the Royal Society of London
Series A, 100(704), 305–329.
Egbert, G. D., and Erofeeva, S., 2002. Efficient inverse modeling of
barotropic ocean tides. Journal of Atmospheric and Oceanic
Technology, 19(2), 183–204.
Foreman, M. G. G., 1977. Manual for Tidal Heights Analysis and
Prediction. Pacific Marine Science Report No. 77–10, Institute
of Ocean Sciences, Patricia Bay, Sidney, BC. http://www.omg.
unb.ca/GGE/5013_LABS/heights.pdf.
Haigh, I. D., Eliot, M., and Pattiaratchi, C., 2011. Modeling global
influences of the 18.6-year nodal cycle and quasi-4.4 year cycle
on high tidal levels. Journal of Geophysical Research-Oceans,
116, C06025, doi:10.1029/2010JC006645.
Masselink, G., Hughes, M., and Knight, J., 2003. Introduction to
Coastal Processes and Geomorphology. London: Hodder Education.
Munk, W. H., and Cartwright, D. E., 1966. Tidal spectroscopy and
prediction. Philosophical Transactions of the Royal Society of
London, A259, 533–581.
Parker, B., 2005. Tides. In Schwartz, M. L. (ed.), Encyclopedia of
Coast Science. Dordrecht: Springer.
Pugh, D. T., 1987. Tides, Surges and Mean Sea Level: A Handbook
for Engineers and Scientists. Chichester: Wiley.
Pugh, D. T., 2004. Changing Sea Levels: Effects of Tides, Weather
and Climate. Cambridge: Cambridge University Press.
Cross-references
Seiche
Storm Surges
Tidal and Nontidal Oscillations
Tidal Asymmetry
Tidal Datum
Tidal Hydrodynamics
Tidal Ranges
TIMESCALE
Lisa V. Lucas
United States Geological Survey, Menlo Park, CA, USA
Definition
Time scale refers to “the time allowed for or taken by
a process or sequence of events” (OUP, 2013).
Essential concepts, application and usage
The above definition provides a general description of the
term “time scale.” In science and engineering practice, a
time scale is typically an estimate expressing a representative, overall magnitude as opposed to a precise value; as
such, time scales (like length, velocity, and other commonly
used scales) are frequently quantified in terms of orders of
magnitude (Cushman-Roisin and Beckers, 2011). A time
scale carries the dimension of time and may be expressed
either in precise temporal units (e.g., seconds, hours, days,
years, decades) or in approximate temporal units (as with
“tidal,” “seasonal,” or “episodic” time scales).
In combination with other scales, time scales may be
used to estimate the relative magnitude (and thus, importance) of individual terms in time-marching equations
(Cushman-Roisin and Beckers, 2011). Time scales may
be defined to describe the rates of physical, biological,
and chemical processes, serving as a common currency
with which to compare their relative speed, and thus
importance (e.g., Koseff et al., 1993; Middleburg and
Nieuwenhuize, 2000; Lucas et al., 2009; Dame, 2012).
In such a context, a smaller time scale suggests a faster
and more dominant process (Lucas, 2010). A time scale
may be estimated as the reciprocal of a first order rate constant or frequency, or from a combination of length, velocity, diffusivity, or other scales such that the remaining
dimension is time (e.g., Fischer et al., 1979; Koseff et al.,
1993). A time scale may reflect the approximate time for
completion of a process, such as for (1) diffusive mixing
over an estuary’s depth (Fischer et al., 1979), (2) advective
transport over the estuary length (MacCready and Banas,
2011), (3) flushing of an estuary by river flow and/or tides
(Sheldon and Alber, 2006), (4) settling of particles through
a water column (de Brauwere and Deleersnijder, 2010),
(5) biomass growth by a factor e (Lucas, 2010), or (6) filtration of a water column or estuary volume by benthic
organisms (Buzzelli et al., 2013).
The term “time scale” may also be used to convey (1) a
typical period of variability or fluctuation in estuarine forcing or ecosystem response (e.g., Litaker et al., 1993; Cloern,
1996; Jay et al., 2000), (2) a period of estuary adjustment to
712
TIMESCALE