Wanderlust World Wanderlust World The ocean surface isn't a level sheet—it's a constantly shifting 3D topography with "hills" and "valleys" spanning meters to hundreds of kilometers.
| Force / Factor | Effect on Sea Surface Height (SSH) | Typical Amplitude |
|---|---|---|
| Earth's gravity (geoid) | Mass concentrations (seamounts, trenches) pull water → permanent "bumps" | ±100 m globally |
| Earth's rotation | Centrifugal force bulges equator ~21 km vs. poles | 21 km equatorial bulge |
| Ocean currents (geostrophic) | Pressure gradients tilt surface across currents (e.g., Gulf Stream ~1 m slope) | 0.5–2 m |
| Temperature / salinity (steric) | Warm/fresh water expands → higher SSH | 0.2–1 m seasonal |
| Atmospheric pressure | Inverse barometer: 1 mbar ≈ 1 cm SSH change | ±0.3 m weather |
| Tides | Astronomical forcing | 0–10+ m coastal |
Satellite altimetry (TOPEX/Poseidon, Jason series, Sentinel-6) maps SSH globally every 10 days to ±3 cm accuracy. These data drive:
We define a reference ellipsoid (WGS84) and a geoid model (EGM2008) to approximate "mean sea level." But the instantaneous ocean surface deviates from both—by meters, predictably. The "same elevation everywhere" idea is a useful datum, not physical reality.