20 00 



1000- 



0- 



-1000 



12 16 20 Z4h 



Fig. 2. 



The analysis of the above result, taking into consideration pilot 

 balloon, surface, and mountain observations,, leads to the following 

 conclusions, as to the mechanism of heat thunderstorms and alteration 

 of vertical lability : — 



'(1) Advedive Change — 



{a) Advection of Cold Air at the Level of Tropopause : The 

 labile energy is very large and exceeds 4,000 joules (mean value). 

 Strong thunderstorm is produced. 



{b) Advection of Cold Air in the Lower Atmosphere : The 

 cold air comes from the Japan Sea side over the Joetu Mount- 

 ains, northern border of the Kwanto Plains, and rides over a 

 heated unstable air stratum stagnant in the Plains in daytime. 

 This unstable stratification causes the labile energy of 2,000- 

 3,000 joules (surface value). Moderate or weak thunderstorm 

 is produced. 



(c) Advection of Southerly Warm Air : When the fresh 

 southerly warm air invades from the Pacific Ocean side, the 

 stratification becomes suddenly stable. This current is of 

 different nature from local sea breeze. 



(2) Non-advective Change — 



(a) Heating From the Ground : The labile energy due to 

 heating alone does not exceed 2,000 joules (surface value) and 

 no thunderstorm is produced, only resulting in the development 

 of moderate or weak cumulo-nimbus. Figure 2 should be 

 interpreted as the mean diurnal variation of labile energy due 

 to surface heating alone. 



(b) Stabilizing Action of Convection : The labile energy is 

 completely consumed within one to two hours by convective 

 motion accompanying cumulo-nimbus. Therefore, in case of 

 no energy supply, the duration of thunderstorm is one to two 

 hours. 



79 



