A preliminary survey of the distribution of micropulsations in the magnetosphere from OGO's-3 and 5

Abstract

Magnetic field data from the OGO-3 and 5 satellites is being systematically scanned to determine the magnetospheric distribution of micropulsations in 7 bands (periods: 0.8 to 2s , 2-5 s , 5-108 , 10-25 s , 25-45s, 45-1208 , and 120-240s ) and incoherent irregularities in two categories (time constants: T < 58 and 5s < T < 45 s ).Although incomplete at this date, the principal features of the distributions are sufficiently evident near the equatorial plane to make preliminary results significant.The characteristics and distribution of Pc-3 waves (10 -45 s ) with a broad dayside maximum roughly independent of distance agrees exceptionally well with well known Pc-3 properties at the earth's surface.Pc -4 (45-1508) distributions are similar to Pc -3 but some difference appears in detail.Waves with Pc-2 periods (5-10 s ) are statistically distributed in close coincidence with the distributions of waves with Pc-1 periods (0.2-5s).Comparitively minor differences occur between the bands 0.8-2s , 2-5s , and 5-10s .The magnetospheric distribution of periods 0.8s to lO s is however completely different than that for periods lO s-120 s .The percentage of time signals appear in the 0.8-10s range has a pronounced maximum within the magnetosphere near the magnetopause and the 6h LT meridian with high percentages extending tailward near the magnetopause.This distribution is similar in many respects to the magnetospheric distribution of incoherent irregularities which statistically supports the observation that 0.8 to lOs waves are most generally, but not always, closely associated with other field irregularities, suggest!-, plasma instability origin.Statistically it would probably be incorrect to label these waves as being Pc (i.e., continuous pulsations) in the satellite data.Waves and recurrent pulses with Pc-3 periodicities frequently constitute the dominant large amplitude fluctuations in the magnetosheath i sunward fr an the dayside magnetopause.It is believed that these waves and recurrent pulses are closely related to the Pc -3 oscillations within the dayside magnetosphere.Support is given to the suggestion that a s Pc-3 activity index based on surface observations should be derived and i be made available as an international service.