t - Comisión Interamericana del Atún Tropical

CURRENTS IN P ANAMA BAY405as blanks in the data record. In the cases in which there were both vectorand blank listings and the number of the former was the larger, the latterwere included in the averaging process by arbitrarily assigning a current ofmagnitude 0.2 knots and direction equal to the mean of the listed directions.This undoubtedly introduced bias of sorne sort into the analysis,but was considered more desirable than the two alternatives of eithermaking the magnitudes zero, or ignoring the observations. When thenumber of blanks exceeded the number of vectors listed for a tide stagethe mean total current was not detern1ined.RESULTSThe end-points of all the total current vectors which could be calculatedfor each depth of observation at each current station are shown inFigure 4. For a complete set of total current vectors there are twentypoints. The circular hatched area or part thereof which appears in sorneof the plots is the threshold region of current speed 0.2 knots or less.Thus the center of the threshold region is the originof the plot. The endpointsof the total current vectors (filled circles) are joined in an orderaccording to tide stage by a solid line if the succession of points is consecutive,or by a broken line if one or more points is missing. The linedrawn between any two points is not always the shortest because an attemptwas made to join the points in a manner such that the reader couldtrace successive points through the tidal cycle. As an aid in this respectthe tide stages corresponding with low water (L), half-tide flood (F), highwater (H), and half-tide ebb (E) at Balboa have been annotated.The lack of data from three current meters was apparently due toeither of two reasons. At Statio11 B tIle meters at 6 a11d 20 ft depth belowthe sea surface appeared to be operational throughout the period ofmeasurement but the currents there were so weak that most (at least80%) of the signals from the meters were indistinguishable from backgroundnoise. On the other hand, at E80 apparently good measurementsof strong currents were made dLlring the first two tidal cycles of the observationperiod at that station, but after that instrument failure seemedto occur.The plots of the end-points of the total current vectors in Figure 4 arethe tidal current figures and the centers of those figures are the end-pointsof the corresponding net current vectors. The vector difference between anypoint of the tidal current figure and the net current vector is the tidalcurrent at the tide stage corresponding to the point.AII of the tidal current figures have a long dimension and for nearlyall of them it is oriented approximately along 330 o -150 o T. The onlymarked exception is that for A40 which has a northeast-southwest alignmenteThere is, however, a large variation in size and form of the figures.