Dynamic spectral characteristics of micropulsation pearls

The dynamic spectrums of micropulsation pearls (type Pc 1) recorded at stations in various latitudes were studied to obtain the frequencies and the spacing times of the fine structure elements comprising pearl events. In confirmation of earlier results, the product of these two parameters is found to be nearly independent of latitude. However, the parameters are themselves functions of latitude, both the spacing time and the reciprocal of the frequency being almost proportional to the L value. These dependences are such as to account for the tendency of the frequency-spacing time product to be constant. An attempt to discriminate between Alfvén wave and particle bunch hypotheses for the generation of pearls was made by comparing the experimental results with computations of the travel time over the field line as a function of latitude. It appears that mirroring particle bunches with a velocity of about 1270 km/sec could account for the observed latitude effect.