Sea surface height changes over the seasons
| The picture above shows the sea surface height for the seasons of one year, with red indicating higher than normal heights, and blue indicating those lower than normal. One of the factors that influences sea surface height is water temperature. Warm water expands, causing the height to increase, while cool water contracts, lowering the surface height. Notice how this is evident in the images. During the summer and fall, when the northern hemsphere is warmest, the sea surface heights in the northern hemisphere oceans have increased. They then decrease during colder winter and spring months. |
Credit: NASA/TOPEX-Poseidon
For more info: http://topex-www.jpl.nasa.gov/education/altimeter-basics.html