During a series of rains, we have often had a period during which we had much rainfall being beyond our comprehension. Selecting two examples from these cases, we have estimated carefully each effects due to topography, large scale disturbance, frontal friction and convective instability. The results of the estimations are shown in this paper. And it is emphasized that the effect due to the convective instability on the amount of precipitation may be of overwhelming magnitude than the other in heavy rain.
First, it is proved that the solution for frictional vorticity equation appears always computationally unstable, so far as the usual centered time difference method is used. As the substitute of the method above, another method to obtain a computationally stable and accurate solution is proposed. The principle is to apply the centered difference method only to the calculation of the advection term, and to apply the forward difference method in Taylor's series expansion form to that of the frictional term.
Dissolved oxygen content in rainwater has been measured in Tokyo by means of the Winklar's titration method since September 1957. The sample of rainwater has been collected in a bottle containing a liquid paraffin. In most rainfalls rainwater was found to be unsaturated with the dissolved oxygen at the time of its arrival to the ground as Miyake and Saruhashi (1949) pointed out, its saturation percentages being between 85 and 100% for rainfalls during the period of September 1957 to March 1958. Snow was found to contain about 6cc oxygen per litre of melted snow, which is about 60% as compared with the oxygen content of saturated water at 0°C and normal pressure. Values of oxygen content for each precipitation were related to the structure of raincloud. This shows that the oxygen content in rainwater has a close correlation with the height of cloud base and with the mechanism of raindrop formation. A possible explanation for the cause of the unsaturation and the significance of the obtained results for studies of precipitation mechanism are discussed.
Dissolved oxygen content in rainwater has been measured in Tokyo by means of the Winklar's titration method since September 1957. The data obtained for the period of the winter-half season have been reported in the previous paper (I). In the present article (II), the data for the summer-half season from April to September are reported. Rains of thunderstorm have been found to be unsaturated with oxygen to a greater extent than other rains. This fact seems to suggest that ice phase predominates in thundercloud more appreciably than in other rainclouds. In this respect, rains o: Typhoon rain-band also are found to have a similar nature. The chloride content in rainwater was found to be larger in the rains of the first type of which the oxygen content seemed to be the saturation at the temperature and pressure in the cloud than in the rains of the second type of which oxygen content seemed to be appreciably less than the saturation in the cloud. This suggests that the rains of the first type tend to occur in a maritime airmass which contains larger amount of salt particles.