Determination of Magnetic Reconnections in a Low and a High Activity Year

Abstract

When there is a temporary disturbance of earth’s magnetosphere, then a geomagnetic storm (or solar storm) has occurred. It is caused by a solar wind shock wave and/or cloud of a magnetic field that interacts with the Earth's magnetic fields. The interaction of Interplanetary Magnetic Fields (IMF) of the sun [1] with the earth’s magnetic fields in opposite directions is known as magnetic reconnection. Magnetic reconnection (often referred as "reconnection") is the breaking and reconnecting of oppositely directed magnetic field lines in plasma at a neutral point which leads to converting the magnetic field energy into plasma kinetic and thermal energy. It occurs either in the day-time (day reconnection) where the sunward convection near the polar cusps allows energised particles to be transmitted earthward or night-time (tail reconnection) where particles are injected into the magnetosphere, thus releasing stored energy in the form of auroral substorms. A geostorm can be determined by changes in the Disturbance-storm time (Dst) Sokolov [2]. However not all geomagnetic storms have an initial phase and not all sudden increases in Dst or SYM-H are followed by a geomagnetic storm. This paper attempts to determine when the magnetic reconnection occurs in the solar cycle 24 considering a low activity year 2009 and a high activity year 2012. We analysed 39 and 202 geomagnetic storms in 2009 and 2012 respectively considering the Dst indices and IMF Bz values of each month obtained from the OMNIWeb database. Our results showed that storms were frequent and intense at high levels of solar activity due to the frequent occurrence of CMEs and ICMEs in the year 2012 than in the year 2009 which occurred in 10% and 45% of days in the year 2009 and 2012 respectively. This study also revealed that negative Bz occurrences were 47.54% and 52.18% of Bz occurrences in 2009 and 2012 respectively. Thus, the more intense the geostorms, the more Bz would go south and the more magnetic reconnection and subsequently auroral substorms which can increase radiation doses for occupants of transpolar flights, disruption of shortwave radio communications, distortion of compass readings in polar regions, failure of electrical transmission lines, increased corrosion in long pipelines, anomalies in the operations of communications satellites, and potentially lethal doses of radiation for astronauts in interplanetary spacecraft.