Abstract: Polymodal Deep-Water Wave-Rider Buoy Data

TANNER, W. F.
Florida State Univ., Tallahassee, FL

Deep-water wave-rider buoys report near-realtime measurements of wave period and wave height off of the shores of the U.S. These records are largely polymodal, commonly with 2 to 4 modes, in some instances with five, six or seven. This information cannot be obtained by observation of breaker lines on the coast itself after shoaling has already modified open-sea characteristics.

Because of this polymodality, calculations of mean period & mean height are not very useful Instead, one needs the modes. The mean may indicate a wave which does not exist in the study area. The significant wave is also suspect; in addition to a poor and arbitrary definition, it probably does not represent any mode at all.

In simulation of shoaling of open-sea waves by computer means, one needs the first mode (the longest period, the highest wave). The shoaling process may increase the polymodality, so that waves obtained at or immediately prior to breaking may be different from what was seen in deep water. In addition, the shoaling process may produce a "zero component" (important time interval on the coast when there are no waves at all; Tanner 1977).

Finally, shoaling may cause truncation of a few modes so that the near-shore wave record may depart still differently from deepsea data.

The new deep-water wave data do not match well with wind and fetch. This may be due to the presence of Langmuir circulation, which provides an important water surface motion that is due to neither waves nor currents. There are also problems with continuity of data from hour to hour, but these may be relatively minor.

AAPG Search and Discovery Article #90932©1998 GCAGS/GCS-SEPM Meeting, Corpus Christi, Texas