. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering Circulation over the shelf of the southeastern Bering Sea 59 FREQUENCY DISTRIBUTION OF HORIZONTAL KINETIC ENERGY One of the most useful ways of examining time- series data of water velocity is to calculate the kinetic energy distribution as a function of frequency. Some of the ocean's processes occur at distinct frequencies, or in discernible frequency bands: often a chaotic jumble in plots of velocity versus time becomes clear when energy versus frequency is plo
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering Circulation over the shelf of the southeastern Bering Sea 59 FREQUENCY DISTRIBUTION OF HORIZONTAL KINETIC ENERGY One of the most useful ways of examining time- series data of water velocity is to calculate the kinetic energy distribution as a function of frequency. Some of the ocean's processes occur at distinct frequencies, or in discernible frequency bands: often a chaotic jumble in plots of velocity versus time becomes clear when energy versus frequency is plotted. The most striking example is the tidal currents, whose frequencies are determined by astronomical constants. For the southeastern shelf, we define three fre- quency categories: mean, low-frequency (subtidal), and tidal. The mean flow is the vector average over a few months or longer. We have in mind the flow over a season or longer, but in practice we have usually defined the mean by the length of the current record. Two tidal periods stood out, diurnal (about 24-hour period) and semidiurnal (about 12-hour period). Low-frequency (long period) flow then fell between seasonal and daily periods. Although there were no definite periods associated with the low-frequency energy, one week was typical. In most records, these three frequency categories contained over 90 percent of the kinetic energy. Tidal frequencies contained most of the energy over the shelf, ranging from 60 percent of the fluctuating energy^ near the shelf break to more than 95 percent in some records obtained inshore of the 50 m isobath. Roughly 80 percent of this tidal energy was semidiurnal, and 20 percent diurnal (Pearson et Chapter 8, this vol- ume, describe the tides more fully). Vector mean speeds were usually 10 percent or less of the mean scalar speeds (Table 5-1), so that the kinetic energy of the mean flow was about 1 percent of the totEil horizontal kinetic energy (KE^^MV^ /2, or per unit mass
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