Auroral-zone pearl pulsations

An analysis has been made of Pc 1 band micropulsations observed in the auroral zone during one solar rotation at Flin Flon, Manitoba, August-September 1964. The Pc 1 band micropulsations were subdivided into pearl pulsations (PP), impulsive activity (IMP), and short irregular pulsations (SIP) this paper is concerned primarily with PP. We have observed: (1) there is no correlation of PP with electron precipitation indicated by bremsstrahlung recorded at balloon altitude; (2) PP type activity occurs at the time of a sudden commencement and can have an hourly repetition of occurrence for 5 or 6 hours thereafter; (3) the Kp and AP indices are too coarse for adequate representation of geomagnetically disturbed times when studying the dependence of PP occurrence on geomagnetic activity; (4) there may be a slight increase of PP period with increase in K; (5) PP have higher amplitudes when K values are higher; (6) Pc 3, 4 band activity may be used as a good predictor for PP occurrence, since, for days rated as disturbed by Pc 3, 4 activity, there is an inverse correlation between PP and Pc 3, 4. For days rated as quiet by Pc 3, 4 activity, PP may occur at any time during the daylight hours; (7) PP are distributed throughout the daylight hours on quiet days, whereas they tend to appear only within an hour or two of 1800 LMT on disturbed days. We can interpret these observations in terms of a hydromagnetic wave packet origin for PP with the occurrence of PP dependent on (1) triggering mechanism; (2) amplification mechanism; (3) guiding along field lines; (4) transmission through the ionosphere.