Level 2
Finding the Mean
The Earth's oceans are not shaped like a perfect sphere of water. Factors such as the shape of the Earth's crust, variations in the planet's gravitational field, winds, and currents cause natural variations in the height of the ocean's surface around the globe. Because of these natural variations, and the fact that the oceans themselves are always in motion, it is difficult to give measurements of sea surface height in absolute terms. Instead, scientists measure the difference between the ocean's height and the expected or average height at any given location.
Understanding the concept of a mean, or average, is important to interpreting water level data at any scale. Satellite-derived sea surface height data and local tide gauge data are both reported as deviations from an expected or mean height.
Use the data in the table below to check your understanding. Then experiment with different factors that affect water levels using an interactive model.
Check your understanding
| Measurement | Height | (- Mean) | Deviation |
|---|---|---|---|
| 1 | 0.2 | ||
| 2 | 0.3 | ||
| 3 | 0.2 | ||
| 4 | 0.2 | ||
| 5 | 0.2 | ||
| 6 | 0.1 | ||
| Total | 1.2 | ||
| Mean |