Atmospheric consequences of cosmic ray variability in the extragalactic shock model: 2. Revised ionization levels and their consequences / Melott Adrian L.,Atri Dimitra,Thomas Brian C.,Medvedev Mikhail V.,Wilson Graham W.,Murray Michael J. // JOURNAL OF GEOPHYSICAL RESEARCH-PLANETS. - 2010. - V. 115, l. .

ISSN/EISSN:

0148-0227 / нет данных

Type:

Article

Abstract:

It has been suggested that galactic shock asymmetry induced by our galaxy's infall toward the Virgo Cluster may be a source of periodicity in cosmic ray exposure as the solar system oscillates perpendicular to the galactic plane, thereby, inducing an observed terrestrial periodicity in biodiversity. There are a number of plausible mechanisms by which cosmic rays might affect terrestrial biodiversity. Here we investigate one of these mechanisms, the consequent ionization and dissociation in the atmosphere, resulting in changes in atmospheric chemistry that culminate in the depletion of ozone and a resulting increase in the dangerous solar UVB flux on the ground. We use a heuristic model of the cosmic ray intensity enhancement originally suggested by Medvedev and Melott (2007) to compute steady state atmospheric effects. This paper is a reexamination of an issue we have studied before with a simplified approximation for the distribution of incidence angles. The new results are based on an improved ionization background computation averaged over a massive ensemble (about 7 x 10(5)) shower simulations at various energies and incidence angles. We adopt a range with a minimal model and a fit to full exposure to the postulated extragalactic background. The atmospheric effects are greater than they were with our earlier, simplified ionization model. At the lower end of the intensity range, we find that the effects are too small to be of serious consequence. At the upper end of this range, similar to 6\% global average loss of ozone column density exceeds that currently experienced due to anthropogenic effects such as accumulated chlorofluorocarbons. We discuss some of the possible effects. The intensity of the atmospheric effects is less than those of a nearby supernova or galactic g ray burst, but the duration of the effects would be about 106 times longer. Present UVB enhancement from current ozone depletion similar to 3\% is a documented stress on the biosphere, but a depletion of the magnitude found at the upper end of our range would approximately double the global average UVB flux. We conclude that for estimates at the upper end of the reasonable range of the cosmic ray variability over geologic time, the mechanism of atmospheric ozone depletion may provide a major biological stress, which could easily bring about major loss of biodiversity. It is possible that future high-energy astrophysical observations will resolve the question of whether such depletion is likely.

Author keywords:

ULTRAVIOLET-RADIATION; FOSSIL DIVERSITY; EARTHS CLIMATE; UVB RADIATION; CYCLES; BIODIVERSITY; MARINE; CANCER; OZONE; TEMPERATURE

DOI:

10.1029/2010JE003591

Web of Science ID:

ISI:000281145700001

Соавторы в МНС:

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Другие поля

Поле	Значение
Month	AUG 19
Publisher	AMER GEOPHYSICAL UNION
Address	2000 FLORIDA AVE NW, WASHINGTON, DC 20009 USA
Language	English
Article-Number	E08002
Keywords-Plus	ULTRAVIOLET-RADIATION; FOSSIL DIVERSITY; EARTHS CLIMATE; UVB RADIATION; CYCLES; BIODIVERSITY; MARINE; CANCER; OZONE; TEMPERATURE
Research-Areas	Geochemistry \& Geophysics
Web-of-Science-Categories	Geochemistry \& Geophysics
Author-Email	melott@ku.edu dimitra@ku.edu brian.thomas@washburn.edu medvedev@ku.edu gwwilson@ku.edu mjmurray@ku.edu
ORCID-Numbers	Thomas, Brian/0000-0001-9091-0830
Funding-Acknowledgement	NASA {[}NNX09AM85G]; NSF {[}PHY090067T, TG-PHY090108]
Funding-Text	This research was supported at Washburn University and the University of Kansas by NASA grant NNX09AM85G. The extensive computer simulations were supported by the NSF via Tera-Grid allocations at the National Center for Supercomputing Applications, Urbana, Illinois, TG-PHY090067T and TG-PHY090108. We thank Tanguy Pierog for assistance in our local implementation of CORSIKA.
Number-of-Cited-References	44
Usage-Count-Last-180-days	1
Usage-Count-Since-2013	5
Journal-ISO	J. Geophys. Res.-Planets
Doc-Delivery-Number	641QV