Question

• Tidal Patterns

a.Describe (or draw) the three basic patterns of water levels for each of the three tidal patterns (diurnal, semidiurnal and mixed) over a 24-hour period. Label your axes! (1 point each; 3 points total).

b.How will these patterns change during a New/Full moon and what are these types of tides called (1 point)?

c.How will these patterns change during a first/third-quarter moon and what are these types of tides called (1 point)?

Answer 1

a) A diurnal tidal cycle is characterized by a single high tide at roughly every 24 hours time period.

A semidiurnal tidal cycle is characterized by two high tides daily of about equal heights occurring roughly about 12 hours apart.

In a mixed tidal cycle, the tides also occur twice daily, but the two high tides and two low tides are unequal in height.

These are shown in the diagram below.

b) During new or full moon (i.e. twice a month), the Sun, Moon and Earth are in along the same line due to which the gravitational pull on the oceans is strongest. In this case the amplitude of the tides (tide height) increases. These are called spring tides.

c) During a first/third-quarter moon, the gravitational pull on the oceans is reduced, leading to the low amplitude tides i.e. tide height decreases. These are called neap tides.