The Lowest Astronomical Tide (LAT) is the lowest level to which the sea can fall due to the gravitational pull of the moon and sun. This phenomenon occurs when the gravitational forces of the moon and sun are at their weakest, resulting in the lowest possible sea level. The LAT is an important concept in oceanography, coastal engineering, and navigation, as it helps predict the minimum water level that can be expected in a given area.
Causes of Lowest Astronomical Tide
The LAT is caused by the combined effects of the gravitational forces of the moon and sun on the Earth’s oceans. The moon has a greater effect on the tides due to its proximity to the Earth, while the sun’s effect is smaller but still significant. When the moon and sun are at their farthest points from the Earth, their gravitational forces are at their weakest, resulting in the LAT. This occurs when the moon is in its apogee (farthest point from the Earth) and the sun is in its aphelion (farthest point from the Earth).
Factors Affecting Lowest Astronomical Tide
Several factors can affect the LAT, including the moon’s elliptical orbit, the sun’s elliptical orbit, and the Earth’s slightly ellipsoidal shape. The moon’s orbit is not a perfect circle, which means that its distance from the Earth varies throughout the month. When the moon is at its closest point (perigee), its gravitational force on the Earth’s oceans is stronger, resulting in higher high tides and lower low tides. The sun’s orbit is also elliptical, which affects the gravitational force it exerts on the Earth’s oceans. The Earth’s slightly ellipsoidal shape also affects the distribution of the oceans, resulting in variations in the LAT at different locations.
| Factor | Effect on LAT |
|---|---|
| Moon's elliptical orbit | Increases or decreases the gravitational force on the Earth's oceans, resulting in variations in the LAT |
| Sun's elliptical orbit | Increases or decreases the gravitational force on the Earth's oceans, resulting in variations in the LAT |
| Earth's ellipsoidal shape | Affects the distribution of the oceans, resulting in variations in the LAT at different locations |
The LAT is also affected by other factors, such as atmospheric pressure and wind. Changes in atmospheric pressure can cause the sea level to rise or fall, resulting in variations in the LAT. Wind can also push water towards or away from the coast, affecting the LAT. Additionally, the Coriolis force plays a significant role in the formation of ocean currents, which can also impact the LAT.
Measurement of Lowest Astronomical Tide
The LAT is typically measured using tide gauges, which are specialized instruments that record the water level at regular intervals. Tide gauges can be installed on the coast or on offshore platforms, and they provide accurate and reliable data on the water level. The data collected from tide gauges is used to calculate the LAT, which is usually expressed as a chart datum, or a reference level that is used as a basis for measuring the height of the tide.
Applications of Lowest Astronomical Tide
The LAT has several practical applications in coastal engineering, navigation, and oceanography. In coastal engineering, the LAT is used to design and construct coastal structures, such as seawalls, jetties, and harbors. In navigation, the LAT is used to predict the minimum water level that can be expected in a given area, which is critical for safe navigation. In oceanography, the LAT is used to study the dynamics of the ocean and the effects of the gravitational forces of the moon and sun on the sea level.
- Coastal engineering: design and construction of coastal structures
- Navigation: prediction of minimum water level for safe navigation
- Oceanography: study of the dynamics of the ocean and the effects of gravitational forces on the sea level
What is the Lowest Astronomical Tide?
+The Lowest Astronomical Tide is the lowest level to which the sea can fall due to the gravitational pull of the moon and sun.
What factors affect the Lowest Astronomical Tide?
+The Lowest Astronomical Tide is affected by several factors, including the moon’s elliptical orbit, the sun’s elliptical orbit, and the Earth’s slightly ellipsoidal shape.
How is the Lowest Astronomical Tide measured?
+The Lowest Astronomical Tide is typically measured using tide gauges, which are specialized instruments that record the water level at regular intervals.
