On the causal relation between nitrogen-oxygen compounds in the troposphere and atmospheric electricity

An atmospheric feedback process is tentatively presented as a possible explanation of the rapid increase of charge densities and field strengths in thunderstorms. This process requires fulfillment of two conditions, viz.: (a) Appreciable amounts of nitrous gases are formed inside the cloud by electrical discharges (mainly by silent ones), thereby increasing the NO₃^’ ion concentration in precipitation particles; (b) When ice crystals break up into pieces, electrical charge separation occurs to an extent depending on the abundance and the distribution of NO₃^’ ions inside the crystals.

Field observations: Statistical analysis of NO₃^’ concentration data from precipitation sampling simultaneously conducted at 700, 1 800 and 3 000 m a.s.l. throughout a five-year period established a definite increase of NO₃^’ abundance with increasing in-cloud turbulence and electrical activity. At 3 000 m, a direct correlation between NO₃^’ concentration in precipitation and the time integral of electrical field strength at 3 000 m was found. The NO₃^’ ion concentration in precipitation was not affected by the number of lightning discharges. Evidently, the combined effect of all corona discharges on or between precipitation particles or cloud droplets determines the increase of NO₃^’ ion concentration in precipitation.

Laboratory measurements. The ion concentration gradient in ice particles prior to fragmentation determines the amount of electrical charge carried by the individual fragments of such particles. The amount of negative charge in a fragment is the greater, the higher its NO₃^’ ion concentration is. Where the distribution of NO₃^’ ions throughout the crystals is homogeneous, no charge separation occurs. These results may explain both the rapid increase and the subsequent collapse of the electrical activity in individual thunderstorm cells, besides clarifying the processes involved in the formation of the principal space-charge zones of a typical thundercloud. Water drops were dropped onto a rapidly rotating ice sphere, and the droplets thrown off by centrifugal force collected on a surrounding electrode; the charge accumulated on the latter was measured. An investigation of the effect of NO₃^’ in the water produced the following result: the charge increases up to a maximum as NO₃^’ concentration is increased from below 0.002 to 0.2 γ NO₃^’ ions/cm³, but declines when the latter level is passed. The charge separation caused by collisions of ice particles with raindrops in the lower layers of a thunderstorm or shower cloud are thus seen to be affected by the NO₃^’ content of precipitation.