t - Comisión Interamericana del Atún Tropical

CURRENTS IN PANAMA BAY403were made that the daily wind exceeded 100 miles/day (about 4 mph)from either sector.REDUCTION OF THE DATAThe choice of the procedure used to reduce the current observationsto the tidal and 11et current comp,onents depended on the apparent reproducibilityor precision of observatio11s at a particular phase of the tide,measured over several tidal cycles, and on which aspects of the flow patterncould be investigated with the data.A cursory examination of the data yielded the trivial result that tidalmotion is an important component of the currents in Panama Bay. Sornepreliminary plots showed two more facts: first, that net Cllrrents existedwhich were of the same arder of magnitude as the maximum tidal currents,and second, that the net currents were not steady, but were subjectto increases or decreases in magnitude over periods ranging up to severaldays. Both of these were anticipated on the basis of the quotations givenabove. 1t was necessary, therefore, to attempt to estimate the net currentsas functions of time before proceeding with the extracting of the tidalmotions from the observations.Because the circulation in the Gulf of ·Panama is known to be sensitiveto the local surface wind stress (Forsbergh 1963), an attempt was madeto correlate the periods of relatively high and low net current with thewinds observed at Balboa. That there was no correlation can perhapsbe attributed to the fact that the survey period was one of weak and variablewinds. This does not discount the possibility that the state of thewind at sorne other place, say iI1 the middle of the Gulf of Panama, maybe a better index of net current in Panama Bay during periods of lightwind at Balboa.An indication of the fact that tidal amplitude may be important isgiven by the usable record from Station A which was made during theperiod 13-15 September, when the tidal range was 17 to 20 ft. This wasthe only part of the record with currents more or less C011siste11tly strongertha11 the threshold value, and therefore was the only piece of record amenableto analysis for components of currents.Further analysis for the time-dependency of the net currents wasfrustrated by the shortness of the usable records from the five stations,and by what must be considered as an iI1herent variability in the currentitself or one introduced by the measuring system (lateral motion of thebuoy from which the current meters were suspended, or oscillation of themeters in a horizontal plane could introduce variability in the observations).This was unfortunate, for it required that the analysis for thetidal motions take the form of averages over several tidal periods, that is,over the entire length of the usable record in all cases, to increase the