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Analysis: ‘Sea Level Goes The Way The Wind Blows…Wind, Pressure Play Major Roles’


Sea Level Goes The Way The Wind Blows…Wind, Pressure Play Major Roles

This is one of those posts about things noticed, remembered, and linked while surfing the web. It is well known that the local sea level is heavily influenced by wind speed and direction as well as barometric pressure. Most people are aware of storm surges associated with hurricanes, for example. The same thing happens on a near-global scale, and some of it is near-permanent. Here is a global map of sea level anomaly from the University of Colorado. Figure 1 is the sea level rise trend since satellite radar altimetry began. In Figure 1, the sea level in the Western Pacific has risen 10 or 12 mm per year, while the eastern Pacific, parts of the Southern Ocean, and a spot in the Atlantic, have fallen by 3 to 5 mm per year, over the satellite era. The next interesting map comes from the European Space Agency (ERA). This map is generated by taking the sea surface height as measured by satellite and subtracting the gravity model from GOCE. The result is the sea surface height over the geoid. Figure 2 is the sea surface height over the Geoid. Note the difference in height between the western Pacific and the Southern Ocean, about 3 meters. The difference in height between the western Pacific and the coasts of North and South America is over a meter. These height differences drive ocean currents. These differences are maintained by wind and pressure differences. If wind and pressure change, the sea level changes accordingly. Next are plots (Figures 3 and 4) from Garza et al 2012, of Sea Level Pressure (SLP), and wind changes over the 1980 to 2009 epoch. The SLP has increased over the eastern Pacific and decreased over the western Pacific. North of 10°N, easterly trade winds have increased in the eastern Pacific and south of 10°N, they have decreased. These small changes, along with thermal expansion, have changed the relative sea level between the two sides of the Pacific Basin by 1%, one centimeter out of one meter. My point is that not all of the western Pacific sea level rise is due to warming, a great deal of it is due to wind and SLP change. Do you remember the controversy last year about the trade winds? One paper had them increasing, due to global climate change; the other had them decreasing due to climate change. They were both right. They were just looking at different parts of the elephant. North of 10° North the winds increased; south of 10° North the winds decreased.  

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