Helium abundance variations in the solar wind: Observations from ULYSSES

Details Helium abundance variations in the solar wind: Observations from ULYSSES Helium abundance variations in the solar wind: Observations from ULYSSES

Jun 1995

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1995sowi.conf...73b&link_type=abstract

International Solar Wind 8 Conference, p. 73

Physics

1

Helium, Solar Wind, Stellar Mass Ejection, Solar Corpuscular Radiation, Abundance, Ecliptic, Ulysses Mission, Latitude

Scientific paper

The abundance of helium in the solar wind averages approximately 4% but has been observed to vary by more than two orders of magnitude from 0.1 to 30%. Physical processes responsible for this variability are still not clearly understood. Previous work has shown a correlation between low He abundance and coronal streamer plasma and between high He abundance and coronal mass ejections (CMEs). We now have out-of-ecliptic data on helium in the solar wind from the plasma experiment aboard Ulysses. Tentative results show that the average high-latitude helium concentration is comparable to the in-ecliptic value for the present phase of the solar cycle, that excursions of the hour-averaged abundance very seldom fall outside the range 2.5 to 6.5%, and that there seems to be very little abundance enhancement associated with CMEs encountered at latitudes greater than 30 deg as opposed to the situation commonly encountered with in-ecliptic CMEs. In addition, preliminary observations of a single CME by both ISEE (in-ecliptic) and Ulysses (out-of-ecliptic) show a considerable He enhancement at ISEE with little or no perturbation of the average value at Ulysses' location. This paper will first present new results from the Ulysses mission up to the time of the meeting on the average abundance of helium in the solar wind as a function of spacecraft position, and will then focus on the out-of-ecliptic results including latitudinal abundance variations and observations of abundance enhancements (or lack thereof) in high-latitude CMEs.

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