A synoptic study of doppler scintillation transients in the solar wind

This paper presents the first synoptic study of Doppler scintillation transients caused by the passage of interplanetary disturbances. It is based on 40,000 hours of 2.3-GHz Doppler scintillation measurements surrounding 15 superior conjunctions of planetary spacecraft during 1979--1983, a period that includes solar maximum. A total of 148 separate transients covering a heliocentric distance range of 5--179 R/sub s/ were detected: 122 by one spacecraft and 26 by more than one. The enhancement in scintillation level (termed EF for enhancement factor) of the transients varied from 2 to 100. The multispacecraft measurements of 22 disturbances showed that they attenuated and expanded as they propagated outward from the Sun with propagation speeds varying from 200 to 2000 km/s. The propagation speed was highly correlated with EF (correlation coefficient of 0.91), showing that EF serves as a good indicator of propagation speed, at least for large EF. The frequency of occurrence was highest near the Sun (within 40 R/sub s/), where it was 0.29 transients/d, and decreased with radial distance, a reflection of the radial evolution of the transients and the sensitivity of the Doppler scintillation measurements to transients. Since the Doppler scintillation measurements are most effective near the Sun, they ideallymore » complement in situ spacecraft observations farther away. An earlier study of nine interplanetary shock waves based on scintillation, Solwind coronagraph, and Helios plasma measurements showed a significantly wider range of shock velocities close to the Sun than near 1 AU. The results of this synoptic study indicate that this is apparently a long-term feature of the solar wind around solar maximum. copyright American Geophysical Union 1988« less

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