Typical cases of the development of cyclones in these areas are 

 analysed, and it is shown that in each area the normal temperature 

 distribution combines with the topography to produce a latent cyclo- 

 genetic field, which under favourable conditions gives rise to actual 

 cyclogenesis. Two important factors contributing to the development 

 of active cyclones are (a) the passage of a deep cyclone far to the south 

 travelling east in the region of lat. 50° to lat. 60° S., and {b) the formation 

 of a " coastal front " in western and southern AustraHa during the 

 summer months. 



The subsequent movement of the secondary cyclones is shown to be 

 controlled by thermal steering from the upper air, and to be usually in 

 an E.S.E. direction. Their future development and influence on the 

 general circulation of the South Pacific is briefly stated. 



The following table gives the frequency distribution of cyclogenesis 

 (frontal waves) in six preferred positions in the Australian and Tasman 

 Sea Region. 



(Period : Two Years) 



Oct. 



to 



Dec. 



! Jan. 

 to 

 March. 



April 



to 

 June. 



July 



to 

 Sept. 



(1) S.E. Indian Ocean bounded 



by lat. 25 and 35° S. ; 

 long. 105 and 115^ E. 



(2) S.W. quarter of Western 



Australia — 250 mile wide 

 strip from W. coast be- 

 tween lats. 25 and 35° S. 



(3) The " head " of the Great 



Australian Bight bounded 

 by lats. 25 and 38° S.; 

 longs. 123 and 133° E. 



(4) Tasmanian region — W., S., 



and E. of Tas. within 200- 

 300 miles of coast 



(5) Central N.S.W. and Northern 



Victoria (west of moun- 

 tains) 



(6) Central and western Tasman 



Sea bounded by lats. 32° 

 and 40° S ; long. 165° E. 

 and east coast of Aust- 

 ralia 



(7) Other areas 



Total 



39 



10 



16 



29 



13 



23 



17 



25 



10 



87 



158 



12 



13 



10 



71 



24 



12 



27 



14 



Y 



23 



11 



25 



56 



126 



15 



14 



70 



21 



63 



49 



52 



32 



50 



17 



284 



23 



17 



18 



11 



18 



100 



49 



