788 EIGHTH PACIFIC SCIENCE CONGRESS 



for the layers from 100 m. to 300 m. deep, the phases of change of water 

 temperature are nearly coincident and the maximum temperatures 

 generally appear between October and December. Moreover, the time 

 of occurrence of the maximum temperature of each layer near the sur- 

 face (0 m.— 100 m. deep) tends to lag with increasing depth. For 

 example, the maximum temperature of the surface layer appears in 

 August, while that of the layer of 50 m. depth appears in October or 

 November. This time-lag may be regarded as mainly due to the effect 

 of eddy conductivity of sea water. If we assume that the said variation 

 of water temperature near the surface is due to the effect of eddy con- 

 duction alone, the amplitude A.^ of the annual variation of water tem- 

 perature of a layer of depth z is expressed by the formula 



A.^A^e-^', ^= J^_ , (1) 



\/XT 



where A^ is the value of ^i, for z = (surface), {i the coefficient of eddy 

 conductivity, and r the period of variation (assumed sinusoidal), of the 

 water temperature. Again, let ^ be the phase lag of the variation of 

 water temperature at the depth z; then 



^=^im-]=y^^7-- <'^ 



If we calculate the value of /.i by the formulae (1) and (2), using the 

 data of oceanographical observations in 1948, we have the results as 

 follows: 



Layer By formula (1) By formula (2) 



m.-50 m. 7.55 2.35 



m.-lOO m. 7.77 4.17 



These values of /<, are not so extravagant in the order of magnitude. 

 However, as seen from the above results, the values of fx calculated by 

 the two formulae (1) and (2) do not agree very w^ell with each other. 

 This is because we have neglected the effect of heat transfer other than 

 that of eddy conduction. 



(b) Long periodic change of xoater temperature. As seen from 

 Figure 2, in the variation of water temperature of each layer, longer 

 and shorter periodic changes other than the annual variation are also 

 recognized. In order to eliminate the anntial variation, if we apply 

 the method of twelve-month moving average to these data, we have 

 the results as shown in Figure 3. 



From this figure we can see that the water temperature was rising 

 from 1948 to 1951 and has been falling since the summer of 1951. As 

 for the cause of this periodic variation, we cannot give any definite 

 explanation for the present, but it seems that this variation is due to 

 a long period change of water mass situation. 



