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Related investigations of pi 2 micropulsations Smith, Brian Paul


Related investigations of irregular, nighttime, type Pi 2 micropulsations were undertaken with regards to the source and occurrence of these geomagnetic fluctuations. In particular, the local times of Pi 2's recorded by a global network of stations, during 1964, were determined. From this, the Pi 2 daily occurrence maximum was observed near 2230 LMT. For this same year (1964), rapid-run magnetograms from Memambetsu, Japan and Wingst, Germany were analyzed. The initial orientation of the impulsive Pi 2 disturbance vectors was observed to be primarily northeast (north-west) before (after) 2230 LMT. These results suggest that Pi 2 source field lines lie near the 2230 LMT meridian. Further investigations of the globally observed Pi 2's were made regarding variations in morphology with magnetic activity. The daily occurrence maximum of Pi 2 was found earlier (later) at 2030 (2330) LMT during intervals of high (low) magnetic activity. In this manner, the longitudinal shift of the Pi 2 source is revealed. A statistical study of solar wind protons observed by Explorer 34 satellite was made during the intervals of high, and of low, magnetic activity. This study showed that the Pi 2 source shift may be due to a change in the solar wind flow direction and/or processes associated with changes in the solar wind proton pressure. Pi 2’s are a train of pulsations having quasi-periods ranging from 40 to 150 seconds and each series lasts about 10 minutes. The periods of Pi 2 micropulsations recorded at Ralston, Canada during 1967 were correlated with simultaneous, Alouette 2 satellite received, VLF radio signals. Some of these VLF emission phenomena, known as 'whistler cutoff’ and 'lower hybrid resonance noise band breakup', indicated the location of the magnetospheric plasmapause. Other emissions, known as ELF, were believed to indicate the plasma sheet inner boundary. The variation of the period of the Pi 2's with the indicated magnetospheric subregion locations showed that Pi 2 period varies systematically with positions of the plasma sheet inner boundary during intervals of magnetic quiescence. The results imply a latitudinal (radial) movement of the Pi 2 source in a region near the plasma sheet inner boundary. Lastly, the rate of Pi 2 occurrence with magnetic activity, during 1964 and 1967, was found to be maximum when the planetary index of magnetic activity, Kp, was 1+ to 2-. The mean Kp index most closely approaches this optimum level during the years of sunspot minimum. Thus, the rate of occurrence result is consistent with the inverse relationship of Pi 2 yearly occurrence with the solar cycle. In summation, the source studies revealed a ‘dynamic’ Pi 2 source, in the sense that it varies both latitudinally and longitudinally. An association was shown between Pi 2 and nightside magnetospheric processes and subregions. The occurrence study indicated that processes generating Pi 2’s are not clear but approach optimum when the Kp level is between 1+ and 2-.

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