TYPHOON FORECASTING AT THE ZI-KA-WEI OBSERVATORY 



By Rev. Fr. E. Gherzi, S. J., Director for Meteorology and Seismology 



We believe that a tropical cyclone (a typhoon) forms out of convection- 

 instabilities in the extreme southern border of the Pacific Ocean air 

 mass — namely, in the Doldrums — the " embroidery of the trades," as 

 it has been called by Sir Napier Shaw. 



These convection-instabilities are a common event over the numerous 

 islands dotting that region which extends from lat. 5° to lat. 15° north 

 of the Equator. 



These convection-instabilities by themselves cannot become typhoons- 

 A kinetic factor is required. This kinetic factor we have found in the 

 intermittent but powerful displacements of the Pacific air mass from 

 east to west. The reason for the bodily motions of such an enormous 

 portion of the troposphere is still a mystery. 



These convection-instabilities, being driven westward, will often, if 

 sufficiently intense, amalgamate to form a larger area of convection, 

 moving westward. The Coriolis force will cause this area to spin and take 

 on the aspect of a tropical cyclone. 



These two factors — thermic and kinetic — seem to us sufficient to 

 explain the formation of a tropical cyclone or typhoon. No " triple 

 point situation " or two different air currents interacting are required. 

 These two last atmospheric conditions might perhaps explain the intensi- 

 fying or the blocking of a typhoon, already formed and already on its 

 track. Such an outside atmospheric interference might also, later on, 

 transform the tropical cyclone into an extra-tropical cyclone, with 

 definite fronts in its structure. 



An interesting datum, never quoted, and one which meets our thermic 

 explanation of the birth of a typhoon is that the temperature in the 

 centre of a tropical cyclone is and remains the same as that of the original 

 convection area — namely, about 27° c. So much so that a typhoon seems 

 cool to the Shanghai people, while it appears warm in the Tokyo region. 

 When the temperature of the centre of a typhoon falls down below 24° c. 

 the storm degenerates rapidly into an extra-tropical cyclone. 



Our theory also explains why, when the typhoon fills up, it becomes 

 again a thundery disturbance, with CuNi instead of the usual StratoNi. 

 We have no knowledge of an extra-tropical cyclone showing the same 

 evolution, when it becomes occluded or filled up, although in an extra- 

 tropical cyclone, contrary to what happens in a full-fledged typhoon, 

 there are always thundery conditions in the S.W. and the N.W. sectors. 

 These extra-tropical cyclones can easily be located by direction-finders, 

 while only the outside border of the typhoon can be followed by this 

 means. 



The future motion of the cyclone can be deduced from the trend 

 of the isobars of the anticyclonic part of the Pacific air mass, to which 

 the cyclone is, so to speak, attached (at least in a normal weather 

 situation) . A typhoon detached from its driving air mass will degenerate 

 quite rapidly. 



■. The.se isobars have been drawn since 1930 for the 3,000 m. level b}' 

 means of the well-known Laplace fornuila, using the simultaneous 

 surface observations from the reporting stations and admitting a tem- 

 perature lapse rate of 0. 6° c. per hundred meters. This weather map 



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