98 



FREQUENCY OF WAVE CONDITIONS 



off South Australia, or something like 300 miles farther south there 

 than in July anil August. 



The alteration that takes place in northern autumn in the prevailing 

 state of the swell is, however, so much smaller in the southern Indian 

 Ocean than it is in the northern, that the winter gradation, along 

 any longitudinal belt that might be chosen, is regularly from a small- 

 er frequency of high swells and larger frequency of low, in the north, 

 to a greater frequency of high, and a smaller frequency of low in the 

 south. In northern summer, by contrast, a high swell is most com- 

 mon in the extreme northern part of the Indian Ocean, on the one 

 hand, and in high southern latitudes on the other, and least common 

 (and with the swell most often low) along the equatorial belt in 

 general and, locally, in the Mozambique Channel. 



The seasonal alteration, from northern summer to winter, in the 

 state of the swell relative to that of the sea, is summarized in table 2G 

 for the relatively calm belt between the equator and latitude about 

 5° S., as well as for the axis of the Southeast Trades which, roughly 

 speaking, are the best developed between about latitudes 10° S. and 

 about 20° S. in northern summer, but between about 15° S. and about 

 25° S. in winter. 



Table 26. — Average percentage frequencies of low and high seas and swells in the 

 South Indian Ocean, along the equatorial belt and along the axis of the Southeast 

 Trades, in northern winter and summer 



