A STATISTICAL-ANALYSIS OF EXTREME EVENTS IN CURRENT VARIATIONS DUE TOINTERNAL WAVES FROM THE AUSTRALIAN NORTH-WEST SHELF

Measurements of current fluctuations due to internal waves obtained fr om two fixed point moorings on the Australian North West Shelf have be en analyzed with the aim of calculating the probability of short-scale , large-amplitude internal waves exceeding particular values. Such wav es are generated as a result of breaking or hydrodynamical instability of the semidiurnal internal tide. The statistical stationarity of eac h record has been checked, and it is shown that the records can be use d for the calculation of the frequency by which currents exceed a part icular value for wave heights (double amplitudes) of less than 60 cm s (-1). The theoretical forms for exceedance frequency from the theory o f extreme statistics have been checked, and it is shown that for one l ocation a power asymptotic provides a slightly better descriptor of th e statistics than an exponential asymptotic and for the other location an exponential asymptotic is found to provide the better fit. The exc eedance frequency for internal waves near the Australian North West Sh elf is found to be less than 1.3 waves per hour. The exceedance probab ility for each location has been calculated using Poisson statistics.