CRRES measurements of energetic helium during the 1990-1991 solar maximum

E. G. Clayton, Louisiana State University
T. G. Guzik, Louisiana State University
J. P. Wefel, Louisiana State University


During the 1990-1991 solar maximum, the CRRES satellite measured helium from 38 to 110 MeV n-1, with isotopic resolution, during both solar quiet periods and a number of large solar flares, the largest of which were seen during March and June 1991. Helium differential energy spectra and isotopic ratios are analyzed and indicate that (1) the series of large solar energetic particle (SEP) events of 2-22 June display characteristics consistent with CME-driven interplanetary shock acceleration; (2) the SEP events of 23-28 March exhibit signatures of both CME-driven shock acceleration and impulsive SEP acceleration; (3) below about 60 MeV n-1, the helium flux measured by CRRES is dominated by solar helium even during periods of least solar activity; (4) the solar helium below 60 MeV n-1 is enriched in 3He, with a mean 3He/4He ratio of about 0.18 throughout most of the CRRES mission 'quiet' periods; and (5) an association of this solar component with small CMEs occurring during the periods selected as solar 'quiet' times.