Role in ambient radiation
Cosmic rays constitute a fraction of the annual radiation exposure of human beings on earth. For example, the average radiation exposure in Australia is 0.3 mSv due to cosmic rays, out of a total of 2.3 mSv.[13]
Effect on electronics
Cosmic rays have sufficient energy to alter the states of elements in electronic integrated circuits, causing transient errors to occur, such as corrupted data in electronic memory devices, or incorrect performance of CPUs, often referred to as "soft errors" (not to be confused with software errors caused by programming mistakes/bugs). This has been a problem in extremely high-altitude electronics, such as in satellites, but with transistors becoming smaller and smaller, this is becoming an increasing concern in ground-level electronics as well.[14] Studies by IBM in the 1990s suggest that computers typically experience about one cosmic-ray-induced error per 256 megabytes of RAM per month.[15]
To alleviate this problem, the Intel Corporation has proposed a cosmic ray detector that could be integrated into future high-density microprocessors, allowing the processor to repeat the last command following a cosmic-ray event.[16]
Cosmic rays were recently suspected as a possible cause of a Qantas Airlines in-flight incident where an Airbus A330 airliner twice plunged hundreds of feet after an unexplained malfunction in its flight control system. Many passengers and crew members were injured, some seriously. After this incident, the accident investigators determined that the airliner's flight control system had received a data spike that could not be explained, and that all systems were in perfect working order. This has prompted a software upgrade to all A330 & A340 airliners, worldwide, so that any data spikes in this system are filtered out electronically. [17]
Significance to space travel
Galactic cosmic rays are one of the most important barriers standing in the way of plans for interplanetary travel by crewed spacecraft.
Role in lightning
Cosmic rays have been implicated in the triggering of electrical breakdown in lightning. It has been proposed that essentially all lightning is triggered through a relativistic process, "runaway breakdown", seeded by cosmic ray secondaries. Subsequent development of the lightning discharge then occurs through "conventional breakdown" mechanisms.[18]
Role in climate change
A role of cosmic rays directly or via solar-induced modulations in climate change was suggested by E.P.Ney in 1959 and by Robert Dickinson in 1975. In recent years, the idea has been revived most notably by Henrik Svensmark; the most recent IPCC study disputed the mechanism,[19] while the most comprehensive review of the topic to date states: "evidence for the cosmic ray forcing is increasing as is the understanding of its physical principles."[20]
Suggested Mechanisms
Henrik Svensmark et al. have argued that solar variations modulate the cosmic ray signal seen at the earth and that this would affect cloud formation and hence climate. Cosmic rays have been experimentally determined to be able to produce ultra-small aerosol particles,[21] orders of magnitude smaller than cloud condensation nuclei (CCN).
According to a report about an ongoing CERN CLOUD research project[22] to detect any Cosmic ray forcing is challenging since on wide spread time scales changes in the Sun’s magnetic activity, Earth’s magnetic field, and the galactic environment have to be taken into account. Empirically, increased galactic cosmic ray (GCR) flux seem to be associated with a cooler climate, a southerly shift of the ITCZ (Inter Tropical Convergence Zone)[citation needed] and a weakening of monsoon rainfalls and vice versa.[22] Claims have been made of identification of GCR climate signals in atmospheric parameters such as high latitude precipitation (Todd & Kniveton), and Svensmark's annual cloud cover variations, which were said to be correlated to GCR variation. Various proposals have been made for the mechanism by which cosmic rays might affect clouds, including ion mediated nucleation, and indirect effects on current flow density in the global electric circuit (see Tinsley 2000, and F. Yu 1999). Other studies refer to the formation of relatively highly charged aerosols and cloud droplets at cloud boundaries, with an indirect effect on ice particle formation and altering aerosol interaction with cloud droplets.[22] Kirkby (2009) reviews developments and describes further cloud nucleation mechanisms which appear energetically favorable and depend on GCRs.[23],[24]
Geochemical and astrophysical evidence
Nir Shaviv has argued that climate signals on geological time scales are attributable to changing positions of the galactic spiral arms of the Milky Way Galaxy, and that cosmic ray flux variability is the dominant "climate driver" over these time periods.[26] Nir Shaviv and Jan Veizer in 2003[27] argue, that in contrast to a carbon based scenario, the model and proxy based estimates of atmospheric CO2 levels especially for the early Phanerozoic (see diagrams) do not show correlation with the paleoclimate picture that emerged from geological criteria, while cosmic ray flux would do.
The 2007 IPCC reports however strongly attribute a major role of anthropogenic carbon dioxide in the ongoing global warming, but as "different climate changes in the past had different causes" a driving role of carbon dioxide in the geological past is neither focus of the IPCC nor purported. Similarly, according a BBC report a 2008 Lancaster University study produced "further compelling evidence showing that modern-day climate change is not caused by changes in the sun's activity".[28]
A comprehensive study of different research institutes was published 2007 by Scherer et al. in Space Science Reviews 2007.[29] The study combines geochemical evidence both on temperature, cosmic rays influence and as well astrophysical deliberations suggesting a major role in climate variability over different geological time scales. Proxy data of CRF influence comprise among others isotopic evidence in sediments on earth and as well changes in (iron) meteorites.
Lacking evidence of an accepted mechanism relating cosmic ray and climate e.g. via cloud cover variation and the challenges to obtain correct historical data on cosmic ray flux at various ranges of energies still lead to controversies[30]
See-also Global warming#Solar variation.
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