Two new time series techniques are employed to study
the diurnal effect between thirty to sixty meters depth in the upper equatorial
ocean. A modified spectral approach is proposed to identify the period
of an unequally spaced series.
Based on the exceedances of mixing activities, a new criterion is
introduced to identify local nights and days.
These two techniques together provide a simple way to demonstrate
the existence of the diurnal cycle in deep stratified layers in the ocean.
Instead of entertaining complicated models, the proposed approach
suggests a simply way to identify the periodicity of an unequally
spaced data set of this nature. Similar diurnal effects are
detected in the analyses of a subsequent data set.
Keywords: Diurnal cycles, Exceedance, Periodogram, Time series,
Unequally spaced data, Viscous dissipation rate.