A Fourier analysis of the magnitudes and timing of the Phanerozoic mass extinctions (MEs) demonstrates that many of the periodicities claimed in other analyses are not statistically significant. ...Moreover we show that the periodicities associated with oscillations of the Solar System about the galactic plane are too irregular to give narrow peaks in the Fourier periodograms. This leads us to conclude that, apart from possibly a small number of major events, astronomical causes for MEs can largely be ruled out.
Periodicity in extinction rates Erlykin, Anatoly D.; Harper, David A. T.; Sloan, Terry ...
Palaeontology,
January 2018, 2018-01-00, 20180101, Letnik:
61, Številka:
1
Journal Article
George Rochester was a Tynesider through and through, and his family on both sides had lived in the area for 200 years. University
appointments took him away, but when in 1955 he had the opportunity ...to return to his roots—the Chair of Physics at Durham—he
accepted with alacrity. He stayed in this city, so close to the Tyne, for the rest of his life.
► Gamma-ray astronomy gives evidence of the galactic origin of CR at GeV energies. ► CR energy spectrum indicates the non-uniform space–time distribution of CR sources. ► Galactic supernova remnants ...(SNRs) are the most likely source of CR up to PeV energies. ► High density of SNR in the inner galaxy creates flatter energy spectrum than locally.
The case is made for most cosmic rays having come from galactic sources. ‘Structure’, i.e. a lack of smoothness in the energy spectrum, is apparent, strengthening the view that most cosmic rays come from discrete sources, supernova remnants being most likely.
Peter Fowler was a distinguished physicist to whom physics was sheer enjoyment and this enjoyment brought delight to those
around him. His students, associates and friends were inspired by his ...infectious enthusiasm, his agility at mental arithmetical
calculation and his distinctive laugh. The fun of discovery, of seeking understanding of what was hidden, characterized all
his work and indeed his approach to life generally.
Svensmark et al. (2009) have recently claimed that strong galactic cosmic ray (GCR) decreases during ‘Forbush Decrease (FD) events’ are followed by decreases in both the global liquid water cloud ...fraction (LCF) and other closely correlated atmospheric parameters. To test the validity of these findings we have concentrated on just one property, the MODIS LCF and examined two aspects: 1) The statistical chance that the decrease observed in the LCF is abnormal. 2) The likelihood of the observed delay (∼5 to 9 days) being physically connected to the FD events. On both counts we conclude that LCF variations are unrelated to FD events: Both the pattern and timing of observed LCF changes are irreconcilable with current theoretical pathways. Additionally, a zonal analysis of LCF variations also offers no support to the claimed relationship, as the observed anomaly is not found to vary latitudinally in conjunction with cosmic ray intensity.
Changes in the galactic cosmic ray (GCR) flux due to variations in solar activity may provide an indirect connection between the Sun's and the Earth's climates. Epoch superpositional (composite) ...analyses of high‐magnitude GCR fluctuations, known as Forbush decrease (FD) events, have been widely used to test this hypothesis, with varied results. This work provides new information regarding the interpretation of this approach, suggesting that FD events do not isolate the impacts of GCR variations from those of solar irradiance changes. On average, irradiance changes of ∼0.4 W m−2 outside the atmosphere occur around 2 days in advance of FD‐associated GCR decreases. Using this 2 day gap to separate the effects of irradiance variations from GCR variations on cloud cover, we demonstrate small, but statistically significant, anomalous cloud changes occurring only over areas of the Antarctic plateau in association with the irradiance changes, which previous workers had attributed to GCR variations. Further analysis of the sample shows that these cloud anomalies occurred primarily during polar darkness, precluding the possibility of a causal link to a direct total solar irradiance effect. This work suggests that previous FD‐based studies may have ineffectively isolated the impacts of GCR variations on the Earth's atmosphere.
Key Points
Composites of Forbush decrease events do not isolate from the effects of TSI
TSI changes correlate to a cloud signal over Antarctica but are not causal
Previous workers incorrectly attributed these anomalies to the effects of GCR
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