A Comment on the Bergeron-Findeisen Precipitation Theory by Means of the Correlation of the Salt and Acid Content of Rain with the Intensity of the Rainfall

Abstract

Indirect evidence as to the prevalence of the Bergeron-Findeisen process⁽¹⁾ in the formation of precipitation may be obtained as follows. If it is assumed, with Findeisen, that ice particles cannot be formed in the atmosphere by the spontaneous freezing of undercooled drops, and if, as is supposed by Bergeron and Findeisen, most of the heavy rain originates as ice crystales, a low salt and acid content would be expected with high rainfall intensities while the rain collected from light intensity falls of rain would be more likely to have a high acid and salt content. Fortunately there has been simaltaneous determinations of the salt and acid content which can be correlated with the intensity of the historical heavy rainfall during June 28-30, 1938 in Tôkyô⁽²⁾. During this period, wind was so steady that there was no marked change in the direction and speed of the wind. In his report on the chemistry of rain, Kita published the following set of chlorine, sulphate and nitrite determinations with the corresponding rainfall intensities.
It will be seen that a well-defined inverse relationship exists between the average amount of rain for one-hour intervals and the corresponding chlorine content. Similar but ill-defined tendencies between the average amount of rain for one-hour intervals and the corresponding ammonia or nitrite content are indicated in the table. It appears that the high chlorinity and acidity for the last period of this heavy rainfall could not have resulted from the cleaning of the impurities from the air by the first part of the rainfall and this is only to be explained on the basis of the inverse relationship concept-which is in accordance with the Bergeron-Findcisen theory.⁽¹⁾
In his paper on the chemistry of rain, Dr. Miyake⁽²⁾ published the following statistical table of chlorine, ammonia and nitrite determinations with the corresponding amount of rainfall in order to show how these contents may vary with the rainfall intensities.
As is indicated in the statistical table, a marked low salt and acid content is generally found with high amount of rainfall while the rain collected from light rainfalls has a relatively high acid and salt content. This is in accordance with the Bergeron-Findeisen theory, but the possibility of the cleaning of the impurities from the air by the first part of the rainfall can be partially used to explain the low chlorine and acid content of relatively heavy rainfall.