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Title:	Analysis of VLF signal perturbations in D-region ionosphere induced by solar flares over Malaysia
Authors:	Mohd Masri Abd Rashid (P62731)
Supervisor:	Mahamod Ismail, Prof. Dr.
Keywords:	Solar flares Ionosphere D-region Electron Universiti Kebangsaan Malaysia -- Dissertations
Issue Date:	21-Jul-2017
Description:	Solar flares release energy in the form of electromagnetic radiation and energetic particles that penetrate into the D-region ionosphere, thus increases the D-region ionization rate and electron density. These D-region ionospheric electron density enhancements perturbed the Very Low Frequency (VLF) signal along the path from a transmitter to a receiver. Although the general effect of solar flares has been reported many times, the solar flare studies using Global Positioning System (GPS) widely used still yet to be understood since it suffered signal degradation. This disadvantage occurs especially when the ionosphere is rapidly changing during peak solar condition or when observations occur at low elevations within equatorial regions. Furthermore, the use of Compound Astronomical Low-cost Low-frequency Instrument for Spectroscopy and Transportable Observatory (CALLISTO) spectrometer network to characterize Coronal Mass Ejections (CMEs) event erupted due to solar flare also have some drawbacks. This is because, the model used to interpret the characteristics of CMEs was developed based on Large Angle Spectrometric Coronagraph 2 (LASCO2) satellite data which is severely unstable during peak and extreme flare conditions. Lacking in facilities and limited data observed under space-weather conditions in the sky of Malaysia have also contributed to inaccurate interpretation of solar flare occurrences. In this thesis, an analysis of signal perturbation in D-region ionosphere induced by solar flare by means of remote sensing technique is presented. Three VLF Transceiver Great Circle Paths with call sign; NWC (19.8 kHz), JJI (22.2 kHz) and NPM (21.4 kHz) were selected. NWC transmitter is located in North West Cape, Australia, JJI in Ebino, Japan, while NPM transmitter is located in Hawaii respectively. The data were recorded at Universiti Kebangsaan Malaysia, with call sign UKM, located in Bangi, Selangor, Malaysia (2.55°N, 101.46°E) using Stanford Atmospheric Weather Electromagnetic System for Observation, Modeling and Education (AWESOME) receiver. The amplitude and phase of the VLF narrowband signals from three man-made VLF transmitters were recorded simultaneously. The amplitude and/or phase of VLF signals observed disclosed that Sudden Ionospheric Disturbance (SID) events occurred due to solar flares. In total, more than 1749 flare events ranging from B-class to X-class flare have been analyzed. 145 events affect the VLF paths. 1604 have no effects and approximately 31 events affect the VLF paths concurrently.The results demonstrate that there is a strong positive correlation (0.81) between the solar X-ray flux intensity and the magnitude of the VLF perturbations. Statistical calculation also indicated that the enhancement of X-ray radiation from the sun during the solar flare event was capable to generate amplitude and phase shift of VLF signal perturbations as high as 10 dB and 130° respectively. The method of VLF remote sensing technique to observe and quantitatively estimates the magnitude of VLF amplitude and phase perturbations associated with flare events was successfully achieved.,Certification of Master's/Doctoral Thesis" is not available
Pages:	126
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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