. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . K5~ CYCLES/DRY . 95Z Figure 5-6. Vertical coiierence squared. The squared co- iierence of BC-5A 20 m with BC-5A 50 m is shown, in clockwise (solid) and counterclockwise (dashed) compo- nents. Highly significant coherences in tidal bands are common to all records. Some also show strong low- frequency coherence and inertial ( CPD, clockwise) coherence. coherent at other frequencies. When the coherence was high, the phase differences were usually small, so that the flow at these
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder . K5~ CYCLES/DRY . 95Z Figure 5-6. Vertical coiierence squared. The squared co- iierence of BC-5A 20 m with BC-5A 50 m is shown, in clockwise (solid) and counterclockwise (dashed) compo- nents. Highly significant coherences in tidal bands are common to all records. Some also show strong low- frequency coherence and inertial ( CPD, clockwise) coherence. coherent at other frequencies. When the coherence was high, the phase differences were usually small, so that the flow at these frequencies was in the same direction at both depths. During strong winds, the low-frequency flow was vertically correlated (see below. Seasonal Variations and Meteorological Forc- ing^ and this probably caused the occasional peaks in coherence at low frequencies. Coherence calculations do not reveal relative speeds, but an examination of Table 5-1 shows that shallow instruments usually recorded faster speeds than deeper ones. This may be instrumental (see Introduction) or it may reflect an actual decrease with depth. Just as it is possible to calculate the vertical coher- ence to help determine whether motions are similar throughout the water column, horizontal coherences calculated between records from different moorings help determine if motions are similEir over broad areas. The low-frequency sticks in data from July 1976 suggested to us that the water motion at low frequencies might be coherent over part of the shelf (see Fig. 5-10); we calculated coherence between BC-5A (50 m), BC-2C (20 m), and BC-6A (50 m). The deep instrument on mooring BC-2C failed, but the current meter at a nominal depth of 20 m was below the pycnocline. Calculations between these instruments showed coherence at separations of 30, 42, and 72 km. Again, the calculated tidal coher- ences squared exceeded (Fig. 5-7). At low frequencies there was also high coherence squared in a broad peak which dec
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