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Interplanetary magnetic field, solar wind and geomagnetic micropulsation

University of British Columbia

Micropulsation signals recorded at the mid-latitude station, Salston, Alberta, are compared with simultaneous Explorer 34 observations of the interplanetary field and plasma. The analysis is divided into two parts. First, a study of the interplanetary parameters controlling Pc3-4 activity is made, and second, spectra of upstream waves and continuous micro-pulsations are compared. A case by case study reveals that Pc3 and Pc4 occurrence is determined by the interplanetary field direction. Pc4 requires a field direction within 30° of the Earth-Sun line, while Pc3 takes place for a wider range of field latitudes and azimuths. On a time scale of the order of hours, the amplitude of Pc3-4 continuous pulsations correlates with the solar wind velocity. Large amplitude events associate with high speed solar wind, while small amplitude events correlate with low speed solar wind. Three dimensional distributions of Pc3 and Pc4 versus the interplanetary field direction are calculated. The distributions are then corrected for the amplitude of the signal and further normalised by the IMF distribution. The resulting distributions show that the field direction-control of Pc3-4 activity is net a result of the IMF distribution, and further, the field direction is also an amplitude-control of these continuous pulsations. They show that Pc4 is equally likely for toward and away sectors, while Pc3 exhibits a significant preference for toward sectors. Finally power spectra of upstream waves are compared with spectra of continuous pulsations. It is found that the spectra of Pc2-4 continuous pulsations are determined by the spectral content of upstream waves. On a time scale of the order of half an hour, the micropulsation spectrum correlates with the transverse components spectra of the upstream waves. On a shorter time scale, the micropulsation spectrum is determined by the peaks, transverse or compressional, that carry the roost power in space. Finally, the spectra of upstream waves and micropulsations are consistent with the existence of fundamental waves in space.

Text

2010-02-11

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http://hdl.handle.net/2429/20109

Astronomy

University of British Columbia

Graduate