Concerning the helium-to-hydrogen number density ratio in very slow ejecta and winds near solar minimum


Near the solar minimum the average value of the helium-to-proton number density ratio is a strong function of speed. The average ratios for both solar ejecta and ambient winds obey approximately the same relation with speed. At the lowest speeds, the ratio takes on small values near and below 0.01. Here winds and ejecta with very slow speeds ( urn:x-wiley:jgra:media:jgra53288:jgra53288-math-0001310 km/s) are examined. STEREO and Wind spacecraft data are employed that were obtained from 2007 to 2010. This was during the prolonged solar activity minimum between cycles 23 and 24. Case event and statistical studies are made with 12 very slow ejecta. The helium-to-proton ratio in very slow ejecta relative to the ratio for very slow winds of comparable speed averaged in an inclusive 1 year period is 1.06. The ejecta and ambient slow winds have, then, nearly the same concentrations on average. The values did not approach 0 with decreasing speed and are shown to deviate from a predicted form. A survey of potential solar sources of very slow ejecta and other inferences based on interplanetary data found a strong correspondence with active regions and a dependence of the properties of very slow ejecta with the solar cycle.

Publication Date


Journal Title

JGR: Space Physics



Digital Object Identifier (DOI)

Document Type