Sea-Level Variability

Climate change related sea-level rise is a well-known impact of a warming global climate. And, at the sub-daily or diurnal (over the course of one day) time scale, the gravitational pull of the Moon and the Sun are the main culprits for our high and low tides. However, weather plays an important role on how the sea-level fluctuates between these two timeframes.

In Earth’s mid-latitudes, of particular importance are the synoptic-scale scale systems that can impact air pressure and winds over the coastal ocean, and create particularly high or low sea-levels on otherwise innocuous days. Sometimes, this can lead to “sunny-day flooding” or “nuisance flooding” into communities built near the coast.

There are three main ways this occurs: 1) the inverse barometer effect – low atmospheric pressure does not exert as much force on the ocean water as high atmospheric pressure does – thus, the ocean level rises; 2) wind-forcing – a constant wind blowing perpendicularly in towards the coastline forces water to build up into mounds, forcing the ocean level to rise; and 3) wind blowing parallel to the coast can initiate Ekman processes, that can cause either downwelling (and rising ocean levels) as surface water moves horizontally towards the coast, or upwelling (and lower ocean levels) when the opposite occurs.

Published Research on Weather & Water: