As anyone who has been on a boat knows, the ocean surface is not flat. It ripples and undulates due to wind and waves, rises with the tidal pull of the moon, expands and contracts as it heats and cools, and billows due to circulation patterns. Sea surface height anomaly data is able to characterize these small- and large-scale changes over weeks and years. An anomaly is the difference between the long-term average for different regions of the ocean and what is actually observed by satellites.
Since 1992, the Ocean Surface Topography Mission has been taking detailed satellite measurements of the height of the ocean surface for weather, climate, and undersea mapping applications. The latest satellite in the OSTM series is Jason-3, which was launched on January 17, 2016 and uses a microwave altimeter sensor to measure changes in the height of the ocean to an accuracy of 2.5 cm.
Measuring these differences allows oceanographers and climatologists to detect patterns of global sea level rise, hurricanes, El Niño and La Niña, eddies, boundary currents. When water warms, it expands and raises the surface of the ocean, so measuring the ocean surface height allows scientists to understand how much heat is stored in the oceans.
The imagery in this dataset shows whether the ocean surface is higher or lower than the average (the average is calculated from 1992-present). In this dataset, redder areas are higher than average and blue areas are below average. Each frame shows the 10-day average beginning on the date listed.