Part I — Mechanism of Heat Thunderstorms 



To inake clear the mechanism of heat thunderstorms or, in recent 

 terminology, air mass thunderstorms, four-hourly radiosonde observations 

 were made from 2nd to 17th August, 1944, at Maebasi, Gunma 

 Prefecture, Kwanto District. 



lOuUs 



6000 



SOOO- 



FlG. 



Figure 1 shows the variation of vertical lability determined from the 

 sequent ascents every four hours, where the abscissa denotes the time of 

 observation and the ordinate the labile energy in joules per 1 kg. air, 

 vertical lability being expressed by vei"tical labile energy itself. Here 

 the labile energy is computed by the parcel method widely applied in 

 adiabatic charts, and becomes positive or negative according as the 

 atmosphere is in conditional instability of real latent type or pseudolatent 

 type (Petterssen, p. 62, 1940). 



The thick lines in the figure denote the energies releasable when a 

 lifting air parcel starts from the ground (which will be referred to as 

 " surface " value later), while the dotted lines denote the mean values 

 when the parcels start from several higher levels, including the ground 

 level (which will be called " mean " value). They both show parallelism 

 except a few cases. 



Figure 2 denotes the mean diurnal variation of vertical lability, the 

 maximum being at 14th-16th. 



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