What feature is common to all tide cycles?

The characteristic of having two high tides and two low tides each day is a fundamental aspect of most tidal cycles, specifically in areas influenced by semi-diurnal tides. This cycle occurs due to the gravitational pull of the Moon and the Sun on the Earth's water bodies, which results in the bulging of water towards these celestial bodies. This creates a pattern where, typically, there are two high tides (the peak of the tides) and two low tides (the troughs of the tides) approximately every 24 hours and 50 minutes, leading to a consistent and predictable tidal rhythm in many coastal regions.

While variations in tide height and the influence of atmospheric pressure do affect tide patterns, they do not universally define the structure of tide cycles. Bi-weekly changes in tide patterns may occur due to the alignment of the Earth, Moon, and Sun but are not a constant feature across all tide cycles, as some areas experience different tidal patterns and timings. Thus, the defining feature of having two high and two low tides daily is the most accurate and representative of all tidal cycles.