Study on extreme geomagnetic events and ionospheric response.

Abstract

Extreme geomagnetic events are geophysical phenomena that result from the violent eruptive nature of the Sun. One type Geospace event is magnetic cloud (MC), which is an attendant of coronal mass ejection (CME). MC-triggered storms can cause injection of particles into the ionosphere. This can result in an enhance ionization and conductivity of upper and middle atmosphere. MC can be identi ed based on geomagnetic parameters and solar wind conditions which show high magnetic eld magnitudes, low ratio of plasma to magnetic pressure, low proton temperature, and smooth rotation of the magnetic eld vector. MC events that occurred on 29 April 2014, 17 March 2015, 31 December 2015 and 13 October 2016 were selected for the study. The hourly average of particle dropouts, precipitation, local ionospheric response and magnetometer variations in the region over South Africa (33:3oS, 26:5oE) are examined during geomagnetic storms triggered by MC. The Geostationary Operational Environmental Satellites (GOES) were inspected for radiation belt particle dropouts during MC events. Energetic particle precipitation associated with MC events are obtained from National Oceanic and Atmospheric Administration (NOAA) Polar Orbiting Environmental Satellites (POES). Results show that particle dropouts and precipitation vary with the arrival of MC. A closer look of the ground based magnetometer and the time history of available daytime E-layer critical frequency from ionosonde indicate that lower ionosphere respond to MC-driven storm.