Atmospheric water vapour of extraterrestrial origin: a discussion of its possible role in Sun-weather relationship.

It is shown that at the present time the influx (or accretion) of extraterrestrial hydrogen to the earth atmosphere makes an insignificant contribution to the concentration of water vapor in the atmosphere. The sources of extraterrestrial hydrogen that are investigated quantitatively are: (1) solar flare protons, (2) galactic cosmic ray protons, (3) solar wind (including auroral) protons, and (4) neutral interstellar hydrogen atoms. None of these sources produces changes of atmospheric humidity that are large enough to explain the empirical and statistical evidence for sun-weather relationships. It is also briefly noted that the influx of solar wind protons or neutral interstellar H-atoms may have been more important during earlier eras in the evolution of the earth atmosphere; it is clear, however, that these favorable conditions cannot be invoked to explain sun-weather relationships on time scales ranging from days to decades.