Whistlers and Magnetic Activity

The relationship between whistlers and magnetic activity was studied using planetary K indices and a whistler occurrence index. This index, W k , is the percentage of observing periods with a given K p value during which at least one whistler was recorded. Data from eight whistler stations which were operated during the I.G.Y. were used. In almost all cases, the value of W k was found to increase with K p up to K p values of 1–3, and then decrease as K p is further increased. The decrease of W k with increasing K p is shown to be due in part to masking of whistlers by very low-frequency emissions, but this does not account for the whole effect. No diurnal variations of the relationship of W k to K p was detected, but a small seasonal change was observed. The formation and destruction of ducts or columns of enhanced ionization in the outer ionosphere are suggested as possible mechanisms for explaining some of the observed effects.