Use of the 3D radon transform to examine the properties of oceanic Rossby waves

One of the most successful applications of satellite-borne radar altimeter data over the oceans in recent years has been the extraction of information about long-wavelength baroclinic Rossby (or planetary) waves, which play a significant role in ocean circulation and climate dynamics. These waves cr oss ocean basins from east to west at speeds of a few centimeters per secon d at midlatitudes. The cross-basin propagation time may therefore be severa l months or even years, and an accurate estimation of the speed of the wave s is important. Methods are reviewed for obtaining information on Rossby wa ve velocity from altimetry data, particularly the two-dimensional Radon tra nsform. Unfortunately, the use of longitude-time plots, although it allows the estimation of the zonal phase speeds, does not give any information on the velocity vector when the propagation of the waves is not purely zonal ( east-west). As shown here, the two-dimensional Radon transform can be gener alized to three dimensions, enabling not only the true propagation velocity component to be determined but also the direction of the waves and thus an y deviation from the pure-westward case. As examples of the application of this extended technique, maps of direction, speed, and energy of Rossby wav es in the North Atlantic Ocean are shown.