Exploratory Study of the Relative Effects of Cosmic Rays on Global Climate Change
Sporadic weather patterns, intense heat and storms occur very frequently in recent years. For instance, according to NASA the year 2012 was the ninth warmest year since 1880 where the temperature at the surface of the Earth has increased by ∼0.6 °C during the last century. The uncertainty of the future climate change deserves a full scientific scrutiny in many aspects of natural processes. Over the past decades, numerous studies have reported the correlations between the Earth’s climate and cosmic ray (CR) flux measured at the surface of the Earth . While the true impact of CRs on the Earth’s climate change is currently far from conclusive, extended efforts of long-term monitoring of cosmic ray flux variations are imperative.
Galactic cosmic rays (GCRs) are the high-energy particles that stream into our solar system from distant corners of our Galaxy and some from outside the solar system. The Earth atmosphere serves as an ideal detector for the high energy CRs which interact with the air molecule nuclei causing propagation of extensive air showers . The primary CR particles are mainly energetic protons (>79%) and about 15% alpha particles, which are originated from supernovae explosions or other astrophysical events. The primary CR particles interact with the molecules in the atmosphere and produce showers of secondary particles (mainly pions) at about 15 km altitude. These pions are decaying into muons which are the dominant particles of radiation (about 80%) at the surface of the Earth. At Georgia State University (GSU), multiple cosmic ray particle detectors have been constructed to measure the flux and energy distributions of the secondary cosmic ray particles .
The work conducted at GSU is focused on the study of the seasonal muon and neutron flux variations and the correlation between the CR flux and the Earth’s dynamic weather patterns . In order to make further predictions regarding the global climate with respect to the CR flux variation, numerical model of muon and neutron flux variations at the surface of the Earth is implemented at variable air densities in the associated atmospheric layers in order to establish the causal relationship between the air density variation and the effects of the CR flux during seasonal changes and to study the atmospheric and space weather.
While there are many cosmic ray detector stations around the world , none measure cosmic ray muons and neutrons simultaneously. The work conducted at GSU has been focused on the simultaneous measurement of muon and neutron flux at the surface of the Earth for monitoring the Earth’s dynamic weather patterns. The measured results have been compared with a numerical model of the cosmic ray shower development in the atmosphere using the Geant4 simulation package [4, 6, 7]. This study indicates that the stratospheric air density variation has the dominant effect on the muon flux change while the density variation in the troposphere mainly influences the fluctuation in the neutron flux .
Earth climate trend is a global phenomenon. The regional air mass fluctuations in the atmosphere can greatly influence the weather pattern variations around the globe. It is therefore critically important to establish a long-term and a real-time worldwide monitoring of simultaneous cosmic ray muon and neutron flux variations, which in turn allows us to determine the atmospheric dynamical changes both in the troposphere and in the stratosphere. Obtained results will serve as a core material for studying multivariable correlations between the CR flux and the variations in space/earth weather and climate. Ultimately, this study will greatly improve the understanding of the climate change on local and regional scale and improve predictions of climate from a season to many decades into the future.
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- Nuclear Physics Group at Georgia State University. http://phynp6.phy-astr.gsu.edu/.
- Dayananda, M., et. al.. arXiv: 1303.7191v (2013).
- World Data Center for Cosmic Rays. http://center.stelab.nagoya-u.ac.jp/WDCCR/.
- Geant4 simulation toolkit. http://geant4.cern.ch/.
- Allison, J., et. al. IEEE Trans. Nucl. Science, 53 (2006).