We describe the use of Helios 2 zodiacal light photometer data to identify, classify, and determine the characteristics of significant white light transient events observed in the interplanetary medium. Data from the north ecliptic pole (+90¿) photometer were used to identify transient flux increases which are interpreted as plasma ''clouds'' of Thomson-scattered radiation from electrons which enveloped the spacecraft or passed north of it. A subset of these events was classified by examining the lower-latitude Helios photometers to determine the temporal evolution and spatial extent of each event. We also examined the in situ plasma and magnetic field data during the time of the white light events. Both the white light and in situ data sets were used to study the characteristics of heliospheric white light transients during a 4-year period from solar minimum (1976) to solar maximum (through 1979). Eighty percent of the classified transient events moved progressively outward from the Sun to the east and/or west of the Helios spacecraft and were classified as solar coronal mass ejections (CMEs).

We determined the frequency of occurrence of these CMEs and found that they increased by at least an order of magnitude from solar minimum to maximum. In 1979, most of the Helios events were found to be associated with major CMEs observed near the Sun by the Solwind coronograph. We used the photometers to determine the brightnesses, durations, outward speeds, and scale sizes for each of the heliospheric mass ejections. The average CME had a brightness increase of 2.3 S10 units in the 90¿ photometer. It had an average duration of 37 hours and speed ≈500 km/s, implying a radial ''flow'' dimension of ~0.4 AU, and a longitudinal width near the Sun of ≈50¿. These results suggest that typical heliospheric CMEs have large dimensions, encompassing large volumes and supplying significant amounts of mass to the inner heliosphere, especially around the solar activity maximum. Because of their large size and our selectrion criteria, nearly all of the white light transients were detected at the spacecraft as in situ density enhancements. Most were also associated with significant enhancements and rotations of the interplanetary magnetic field, and many showed evidence for the passage of ''magnetic clouds.'' About half were associated with fast MHD shocks. A small subset (27%) of the white light events showed evidence of corotation from east to west in the lower-latitude photometers and may represent the detection of coronal streamers in the interplanetary medium. ¿ American Geophysical Union 1990