liminfoTide Reference
Free reference guide: Tide Reference
About Tide Reference
The Tide Data Reference is a comprehensive oceanographic guide covering all aspects of tidal science across eight categories: Basic Concepts (tide mechanics, tidal force, spring tides, neap tides), Tide Types (semidiurnal, diurnal, mixed tides, form number classification), Tidal Constituents (M2, S2, K1, O1 with periods and amplitudes), Tidal Prediction (harmonic analysis and prediction formulas), Datum/Reference levels, Tidal Currents (flood/ebb, reversing/rotary patterns, tidal energy), Anomalous Tides (storm surge, tidal anomaly, sea level rise), and Observation Equipment.
Each entry provides quantitative data essential for coastal engineering, navigation, and marine science. The tidal constituents section lists precise periods (M2: 12.42 hours, S2: 12.00 hours, K1: 23.93 hours, O1: 25.82 hours), explains their astronomical causes, and describes how they combine to produce spring-neap cycles and diurnal inequality. The prediction section presents the full harmonic prediction equation h(t) = Z0 + Sum[fi*Hi*cos(Vi+ui-gi)] with definitions of all parameters.
The reference includes Korea-specific tidal data, covering average tidal ranges at major ports (Incheon 7.0m, Gunsan 5.5m, Busan 1.2m, Sokcho 0.3m), the Sihwa tidal power station (254 MW), maximum tidal current speeds at Myeongnyang Strait (6-7 knots), and KHOA (Korea Hydrographic and Oceanographic Agency) observation services. Storm surge data includes the Typhoon Maemi 2003 case study with a +2.4m surge at Masan.
Key Features
- Complete tidal constituent data for M2, S2, K1, and O1 with precise periods, amplitudes, and astronomical causes
- Form number (F) classification formula for determining semidiurnal, mixed, and diurnal tide types
- Full harmonic prediction equation with parameter definitions for tidal height forecasting
- Datum reference levels including ALLW, MSL, MHHW, and MLLW with height ordering relationships
- Tidal current patterns covering flood/ebb cycles, reversing and rotary currents, and slack water timing
- Storm surge mechanics explaining pressure drop effects (1cm per hPa) and wind setup calculations
- Korea-specific port tidal range data for Incheon, Gunsan, Mokpo, Busan, and Sokcho
- Observation equipment reference covering float, pressure, ultrasonic, radar, and GNSS tide gauges
Frequently Asked Questions
What causes tides?
Tides are caused by the gravitational tidal force, which is the difference between the gravitational attraction and centrifugal force from the Moon and Sun. The Moon contributes about 69% of tidal force (closer distance despite lower mass), while the Sun contributes about 31%. Tidal force is inversely proportional to the cube of the distance, which is why the closer Moon dominates despite the Sun being far more massive.
What is the difference between spring tides and neap tides?
Spring tides occur at new moon and full moon when the Moon and Sun are aligned, combining their tidal forces for maximum tidal range (120-130% of average). Neap tides occur at first and third quarter moons when the Moon and Sun are at right angles, partially canceling each other for minimum tidal range (70-80% of average). The spring-neap cycle repeats approximately every 14.8 days.
What is the M2 tidal constituent?
M2 (principal lunar semidiurnal) is the largest tidal constituent with a period of 12.42 hours (12h 25m 14s). It is caused by the Moon gravitational force and accounts for approximately 50% of global tidal energy. At Incheon, Korea, the M2 amplitude is 2.79m. When M2 and S2 (solar semidiurnal, period 12.00h) are in phase, spring tides occur; when out of phase, neap tides result.
How do I determine if a location has semidiurnal or diurnal tides?
Calculate the form number F = (K1 + O1) / (M2 + S2), where K1, O1, M2, S2 are constituent amplitudes. If F < 0.25: semidiurnal; F = 0.25-1.5: mixed mainly semidiurnal; F = 1.5-3.0: mixed mainly diurnal; F > 3.0: diurnal. Korea examples: west coast F = 0.1-0.2 (semidiurnal), south coast F = 0.5-1.5 (mixed), east coast F = 2-5 (diurnal).
How does tidal prediction work?
Tidal prediction uses harmonic analysis to decompose observed tidal records into constituent sinusoidal components. The prediction formula is h(t) = Z0 + Sum[fi*Hi*cos(Vi+ui-gi)], where Z0 is mean sea level, Hi is constituent amplitude, gi is phase, and fi/ui are astronomical correction factors. A minimum of 29 days (one synodic month) of observations is needed, with 369 days or more for precise analysis.
What is a storm surge?
A storm surge is an abnormal rise in sea level caused by low atmospheric pressure and strong onshore winds during typhoons or extratropical cyclones. The pressure effect raises water by approximately 1 cm for each 1 hPa pressure drop. The wind effect pushes surface water toward shore. The actual water level equals predicted astronomical tide plus the storm surge. Typhoon Maemi (2003) produced a +2.4m surge at Masan, Korea.
What tidal range does Incheon have?
Incheon on Korea west coast has an average tidal range of approximately 7.0 meters, with spring tidal ranges reaching 9.3 meters. This is one of the largest tidal ranges in the world, resulting from the amplification of semidiurnal tidal waves in the shallow Yellow Sea. For comparison, Busan (south coast) averages only 1.2m, and Sokcho (east coast) averages 0.3m.
What types of tide gauges are used?
Five main types are used: float gauges (float on water surface with wire and recorder), pressure gauges (subsurface pressure sensor converting hydrostatic pressure to water level), ultrasonic gauges (measuring time-of-flight to water surface), radar gauges (microwave reflection), and GNSS buoys (satellite positioning for sea level). Korea KHOA operates approximately 50 tide gauge stations nationwide.