DMCA
Refraction of swell by surface currents
| Citations: | 1 - 0 self |
BibTeX
@MISC{Gallet_refractionof,
author = {Basile Gallet and William R. Young},
title = {Refraction of swell by surface currents},
year = {}
}
Share
 |
 |
 |
 |
||
OpenURL
Abstract
Using recordings of swell from pitch-and-roll buoys, we have reproduced the classic observations of long-range surface wave propagation originally made by Munk et al. (1963) using a triangular array of bottom pressure measurements. In the modern data, the direction of the incoming swell fluctuates by about ±10 ◦ on a time scale of one hour. But if the incoming direction is averaged over the duration of an event then, in contrast with the observations by Munk et al. (1963), the sources inferred by great-circle backtracking are most often in good agreement with the location of large storms on weather maps of the Southern Ocean. However there are a few puzzling failures of great-circle backtracking. For example, in one case, the direct great-circle route is blocked by the Tuamoto Islands and the inferred source falls on New Zealand. Mirages like this occur more frequently in the bottom-pressure observations of Munk et al. (1963), where several inferred sources fell on the Antarctic continent. Using spherical ray tracing we investigate the hypothesis that the refraction of waves by surface currents produces the mirages. With reconstructions of surface currents inferred from satellite altime-try, we show that mesoscale vorticity significantly deflects swell away from great-circle propagation so that the source and receiver are connected by a bundle of many rays, none of which precisely follow a great circle. The ±10 ◦ directional fluctuations at the receiver result from the arrival of wave packets that have travelled along the different rays within this multipath. The occasional failure of great-circle backtracking, and the associated mirages, probably results from partial topographic obstruction of the multipath, which biases the directional average at the receiver. 1.
Keyphrases
surface current great-circle backtracking tuamoto island modern data good agreement wave packet great circle southern ocean satellite altime-try new zealand puzzling failure classic observation directional average many ray bottom pressure measurement occasional failure inferred source different ray time scale spherical ray incoming direction receiver result bottom-pressure observation incoming swell fluctuates antarctic continent large storm associated mirage weather map directional fluctuation several inferred source great-circle propagation partial topographic obstruction triangular array mesoscale vorticity pitch-and-roll buoy direct great-circle route long-range surface wave propagation
