OCEANOGRAPHIC CLIMATE OF HAWAIIAN ISLANDS REGION 



391 



NORTH LATITUDE 



Figure 17. — Meridional pro61e at 160° W. of the net heat 

 exchange and its equivalent rate of change of surface 

 temperature during June and December. 



temperature during those months would vary 

 from about +4.5 °C. mos."' to —1.0 °C. mos.-', 

 respectively, again reflecting the effect of the 

 seasonal change in the depth of mixed layer. 



In the siu'face temperature discussion reference 

 was made to the northward increase in the seasonal 

 temperature range (figs. 5 and 7). For example, 

 at 12° N. it is only 1.7 °C., whereas at 26° N. it 

 is 5.3° C. Figure 17 shows that the seasonal 

 range in the rate of change of temperature attrib- 

 utable to the net heat exchange to be only 0.2° C. 



619237 O— 62 i 



mos.-' at 12° X., but 2.7° C. at 26° N. On the 

 basis of the seasonal range of the net heat ex- 

 change, one would therefore expect a northward 

 increasing, seasonal temperature range. 



In the discussion of figure 7 reference was also 

 made to the break in the meridional temperature 

 gradient at 22° N. during November to May. 

 This was attributed to a boundary of climatic 

 significance. Such a boundary would be one 

 south of which the net heat exchange is positive 

 throughout the year and north of which it is posi- 

 tive during the summer and negative during the 

 winter. Figure 17 shows this to occur at about 

 13° N. rather than at 22° N. as anticipated from 

 figure 7. Further examination of figure 17, how- 

 ever, shows that the effect of the depth of the 

 mixed layer is such that the monthly tempera- 

 ture change due to net heat exchange, although 

 negative, remains negligibly small (0.1°C. mos."') 

 to 20° N. Therefore, again on the basis of net 

 heat exchange as expressed in temperature change 

 per month, one would expect the meridional tem- 

 perature gradient to increase north of 20° N. 



To show the mean meridional profile, between 

 150° W. and 180°, of the net heat exchange and 

 its effect on the change of surface temperature, 

 figure 18 has been included. It is similar to 

 figure 17, except that it shows the net heat 

 exchange to be positive throughout the year 

 south of 18° N. Thus, certain features in the 

 distribution of surface temperature appear to be 

 associated with the net heat exchange across the 

 sea surface. 



Finally, the chmatic boundarj- referred to 

 above (where tlie negative change of temperature 

 due to heat exchange becomes greater than 0.1° C. 

 per month) may be of dynamic and biological 

 significance. In those latitudes where the net 

 heat exchange is always positive, it has a stabilizing 

 influence on the water column tliroughout the 

 year. To the nortli of tlie boundary, where the 

 effect on the temperature decline is no longer 

 negligible, the net heat exchange has a stabilizing 

 effect tending to oppose the effect of wind stirring, 

 during part of the year, antl during the remainder 

 of the year, when it is negative, tends to aid the 

 effects of wind stirring l)y convection. 



Biologically this boundary may be regarded as 

 one which separates high and low latitude indices 

 of production. For example, on the low latitude 

 side nutrients in the water and plankton standing 



