Environmental & Ecological Modeling

Amphidrome

October 29, 2011, 8:21 am
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World oceans map showing amphidromic points. Source: California State University Long Beach

An amphidrome is a stationary ocean point around which tides rotate in a counterclockwise (clockwise) sense in the northern (southern) hemisphere, i.e. the point about which the cotidal lines radiate.

This article is written at a definitional level only. Authors wishing to expand this entry are inivited to expand the present treatment, which additions will be peer reviewed prior to publication of any expansion.

The vertical range of the tide increases with distance away from the amphidrome, with the amphidrome itself the spot where the tide vanishes to zero (or almost zero). This is also called an amphidromic point.

caption This map shows the patterns of tidal energy played out across the surface of the Earth as lines of force. The colors indicate where tides are strongest, with blues being weaker areas and reds being stronger. In almost a dozen places on this map the lines appear to converge, as if pulled together like a purse. Notice how at each of these places the surrounding color--the tidal force for that region--is blue. These convergent areas are called amphidromes, places where there is little or no apparent tide. This is not to say that the surface of the ocean in these places doesn't move, doesn't rise and fall with wind, momentum, inertia, and other forces acting on it. But for the purposes of studying the tides from space in an effort to understand how energy is conserved and distributed, these areas a mathematically still. Source: NASA

The dozen tidal amphidromes observed in the ocean are critical points that determine the fundamental pattern of the global tidal system. Exploration of recently available satellite data with an unprecedented 1-2 decades duration suggests that an amphidrome is not a tide-only phenomenon in the ocean. Analysis of altimeter-derived sea level anomaly (SLA) data and radiometer-derived sea surface temperature (SST) data allows ten amphidromic points to be clearly identified in annual SLA and SST variations. These amphidromes are located in the tropical areas of the Pacific, Atlantic, and Indian Oceans. Their existence implies that the annual cycle (in time) of the atmosphere-ocean system is translated into a rotary variation (in space) for many of the geophysical parameters. It can be concluded that annual amphidromes are common, the knowledge of which is of particular interest, given their annually "constant" nature, for the monitoring and understanding of oceanic, climatic, as well as biological variabilities at seasonal to decadal scales, which strongly affect many aspects of the natural and societal activities on the globe. - Chen and Quartly (2005)

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Citation

Baum, S. (2011). Amphidrome. Retrieved from http://www.eoearth.org/view/article/51cbece97896bb431f68e6d0

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