Interplanetary Neutral Particle Fluxes Influencing the Earth's Atmosphere and the Terrestrial Environment

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 1996-11, Vol.124 (1), p.209-219
• Main Authors: Bzowski, Maciej, Fahr, Hans J., Ruciński, Daniel
• Format: Article
• Language: English
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1006/icar.1996.0199

It is well known that the Solar System is swept over by neutral interstellar gases, primarily hydrogen and helium, entering the heliosphere from the upwind side and penetrating inward, even up to the orbit of the Earth. The Earth on its orbit is thus moving through this density field and is intercepting time-variable hydrogen and helium fluxes. Quantitatively, this is associated with a sensitive reaction of the density fields to time-dependent conditions of the solar radiation pressure and the ionizing solar radiations during the solar activity cycle. As we shall show, the density distribution of interstellar hydrogen along the orbit of the Earth is strongly varying during the solar cycle. In connection with the variation of the mean relative velocity of this gas with respect to the orbiting Earth a highly variable hydrogen inflow into the Earth's atmosphere will be induced. There is also an additional source of hydrogen influencing the Earth's environment due to the fact that neutral interstellar hydrogen and helium are neutralizing solar wind protons by charge exchange inside the orbit of the Earth, thereby producing an antisolar flux of keV-energetic hydrogen atoms impinging onto the Earth's atmosphere. These time-variable fluxes could be directly monitored by gas detectors of an advanced technology. They might also be indicated by indirect terrestrial effects. We are investigating the question of whether and how these time-variable inflows could be recognized by careful studies of relevant upper atmospheric reactions. We study particle-induced energy inputs and ionization rates in the upper atmosphere and analyze influences on the hydrogen geocorona. We also study the process of relaxation of the inflowing hydrogen within the terrestrial atmosphere and investigate the reaction of atmospheric hydrogen densities to these variable inflows. While it is shown that the induced short-period variation of upper atmospheric hydrogen densities is of negligible amplitude at the present epoch, long-periodic variations of the hydrogen inflow like those connected with the entrance of the Solar System into a region of increased interstellar density at earlier or later eons clearly give their imprints even at lower heights and could even be reflected in ozone depletions induced by increased hydrogen densities at heights of around 50 km. At present anomalous variations of the geocoronal H-1216 A and He-584 A glows uncorrelated with the solar resonance line illumination