Abstract

Solar flares are known to produce fast Corona Mass Ejections (CMEs) that can lead to the occurrence of different classes of geomagnetic storms. Severe geomagnetic storms can generate disturbances in the magnetosphere and the ionosphere that can affect communication channels; by disrupting Satellite and navigation systems, such as GPS, Galileo, Compass and GLONASS. During intense Solar flares, enhancement in the ionospheric electron density usually occurs, leading to the absorption of the High Frequency (HF) signals by the ionosphere. Enhancement in the Very Low Frequency (VLF) radio waves (3 – 30 kHz) usually takes place during solar flares. This phenomenon is called Sudden Ionospheric Disturbance (SID). These SIDs serves as an opportunity for the tracking of solar flares using VLF. In this study, the diurnal variation of the VLF signals transmitted from six locations selected from USA, Australia and Japan were used to monitor SIDs. The signals were received using the 0-50 kHz frequency receiver (Super SID Monitor) installed at the Kebbi State University of Science and Technology (KSUST), Aliero, Nigeria (latitude: 12.31°N and Longitude: 4.50°E). The diurnal variation of the VLF signals alongside some magnetic indices (Dst, kp, and ap), solar wind speed and density as well as the solar flux index (f10.7) for the month of February, 2020 was investigated. Results from this study reveal that; the VLF amplitudes appeared to be stronger when the lowest level of the geomagnetic activity was recorded across all stations on the quietest day of the month. During this day, the intensity of the signals received vary across the stations, ranging from 2*10<sup>4</sup> to 4*10<sup>7</sup>dB. During the disturbed period, decrease in the Disturbance Storm Time (Dst) index was observed to have two minimum excursion with values of -31 and -33 nT, thus indicating a weak geomagnetic storm (-30<Dst>-50) event. Consequently a gradual increase in the solar wind speed with a peak value of 520 km/s, significant decrease in the VLF amplitude ranging from 50 – 7*10<sup>5</sup>dB was observed during the weak geomagnetic storm, on 19 February, 2020. It is also evident from this study that the intensity/strength of the VLF signal and its pattern of propagation are greatly affected by the geomagnetic storm. In spite of the changes in the VLF amplitude observed, there was no trace of solar flares during the weak geomagnetic storm. This therefore suggests that not all classes of geomagnetic storms are connected to solar flares.

Highlights

  • The ionosphere is the major region of the atmosphere that is primarily responsible for radio wave propagation

  • Solar flares travel with the speed of light and they can reach the earth within 480 seconds upon eruption from the sun, emitting radiation from radio waves to gamma rays that is across all electromagnetic spectrum [2]

  • The present study is aimed at; monitoring Sudden Ionospheric Disturbance (SID) using Very Low Frequency (VLF) signals received from six VLF transmitting stations, verifying the quiet and disturbed day morphology of SESSID data received at Kebbi State University of Science and Technology (KSUST) Aliero, track solar flares using Super SID receiver and investigate the relationship between solar flares and pre-magnetic/weak geomagnetic storm signatures

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Summary

Introduction

The ionosphere is the major region of the atmosphere that is primarily responsible for radio wave propagation. The present study is aimed at; monitoring Sudden Ionospheric Disturbance (SID) using Very Low Frequency (VLF) signals received from six VLF transmitting stations, verifying the quiet and disturbed day morphology of SESSID data received at KSUST Aliero, track solar flares using Super SID receiver and investigate the relationship between solar flares and pre-magnetic/weak geomagnetic storm signatures. Studies of this nature are of immense importance to the understanding of space weather. This is the very first time VLF signals are been received and studied during both quiet and disturbed conditions from this location

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