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Title: Study of solar flare induced D-region ionosphere changes using VLF amplitude observations at a low latitude site
Authors: Tan, L M
Thu, N N
Ha, T Q
Marbouti, M
Keywords: D-region ionosphere;Solar flare;VLF amplitude perturbations;Electron density profile;Reflection height;X-ray irradiance;Sharpness factor
Issue Date: Jun-2014
Publisher: NISCAIR-CSIR, India
PACS No.: 96.60qe; 94.20 de; 94.20.wq
Abstract: About 26 solar flare events from C2.56 to X3.2 classes were obtained and analyzed at Tay Nguyen University, Vietnam (12.56°N, 108.02°E) during May – December 2013 using very low frequency remote sensing to understand the responses of low latitude D-region ionosphere during solar flares. The observed VLF amplitude perturbations are used as the input parameters for the simulated Long Wavelength Propagation Capability (LWPC) program, using Wait’s model of lower ionosphere, to calculate two Wait’s parameters, viz. the reflection height (H’) and the sharpness factor (β). The results reveal that when X-ray irradiance is increased, β increased from 0.3 to 0.506 km-1, while H' decreased from 74 to 60 km. The electron density increased at the height of 74 km with 1-3 orders of magnitude during solar flares. These phenomena can be explained as: the ionization due to X-ray irradiance becomes greater than that due to cosmic rays and Lyman-a radiation, which increases the electron density profile. The present results are in agreement with the earlier results. The 3D representation of the electron density changes with altitude and time supports to fully understand the shape of the electron density changes due to X-ray flares. The shape variation of electron density is roughly followed to the variation of the amplitude perturbation and keeps this rule for different altitudes. It is also found that the electron density versus the height in lower latitude D-region ionosphere increases more rapidly during solar flares.
Page(s): 197-204
ISSN: 0975-105X (Online); 0367-8393 (Print)
Appears in Collections:IJRSP Vol.43(3) [June 2014]

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