ABSTRACT
Galactic cosmic rays are modulated in the hliosphere primarily due to the global merged interaction regions with intense magnetic field which leads to a decrease in the galactic cosmic rays throughout the heliosphere. Using long term averages of solar wind (SW) component parameters in addition to cosmic ray count rates of two high latitude Neutron monitor stations (Apatity and Thule) and two mid latitude stations (Newark and Tbilisi) with different rigidity cut-offs, we analyzed the effect of these SW components on the counts rates under different interplanetary magnetic field (IMF) disturbance levels. From first order partial correlation, we found that the total interplanetary magnetic field (Total B) was the most dominant modulating parameter especially during quiet conditions and the solar wind dynamic pressure (SWDP) was more effective during disturbed conditions. The influence of the more subtle parameters like solar wind speed (SWS), Z component of IMF (Bz) and solar wind density were masked by these dominant parameters vis IMF (Total B) and SWDP. Also, cosmic ray count rates on these stations studied showed similar annual variation trend, with station of lowest cut-off rigidity having highest amplitude and vice versa, confirming cut-off rigidity as another important modulating factor.
CHAPTER ONE
1.1 COSMIC RAYS
The cosmic rays (CRs) are energetic charged subatomic particles originating from the outer space with lifetime of the order 106 years or longer, incident at the top of the terrestrial atmosphere and produce showers of particles on interaction with the atmosphere which penetrate and impact the earth’s atmosphere and sometimes reach the earth’s surface. Apart from particles associated with solar flare, cosmic Rays come from outside the solar system. The incoming charged particles are modulated by the solar wind, the expanding magnetized plasma generated by the sun, which decelerate and partially excludes the lower energy cosmic rays from the inner solar system. CRs are mostly pieces of atoms: protons, electrons, and atomic nuclei which have had all of the surrounding electrons stripped during their high-speed (almost the speed of light) passage through the space.
The need to study cosmic rays and their interaction with earth is driven by the understanding that CRs are the major source of ion production in the lower atmosphere (troposphere and stratosphere), therefore, the electrical properties of the atmosphere such as atmospheric electric current, lightening production and thunder cloud formation e.t.c., can be affected by cosmic rays (Ermakov and Komozokov, 1992). It also damages micro-electronics and life outside the protection of the atmosphere and Geomagnetic field. CRs have sufficient energy to alter the state of element in electronic integrated circuit, causing transient errors to occur, such as corrupted data in electronic memory devices or incorrect performance of central processing unit (CPU). It ionizes the nitrogen and oxygen molecules in the atmosphere which leads to a number of chemical reaction; and is responsible for the continuous production of a number of unstable isotopes in the atmosphere of the earth, such as carbon 14 (14C).
n + 14N à P + 14C 1
Cosmic Rays are one of the most important barriers standing against interplanetary travel and pose threat to electronics placed aboard outgoing probe. Magnetic shielding for spacecraft have to be considered in order to minimize damages to electronics and human by cosmic rays ( Nancy, 2005).
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