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Modeling of temporal variation of very low frequency radio waves over long paths as observed from Indian Antarctic stations
Author(s) -
Sasmal Sudipta,
Basak Tamal,
Chakraborty Suman,
Palit Sourav,
Chakrabarti Sandip K.
Publication year - 2017
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
eISSN - 2169-9402
pISSN - 2169-9380
DOI - 10.1002/2016ja023812
Subject(s) - zenith , signal (programming language) , solar zenith angle , amplitude , physics , radio propagation , very low frequency , wavelength , geodesy , remote sensing , variation (astronomy) , optics , meteorology , geography , atmospheric sciences , astrophysics , computer science , astronomy , programming language
Characteristics of very low frequency (VLF) signal depends on solar illumination across the propagation path. For a long path, solar zenith angle varies widely over the path and this has a significant influence on the propagation characteristics. To study the effect, Indian Centre for Space Physics participated in the 27th and 35th Scientific Expedition to Antarctica. VLF signals transmitted from the transmitters, namely, VTX (18.2 kHz), Vijayanarayanam, India, and NWC (19.8 kHz), North West Cape, Australia, were recorded simultaneously at Indian permanent stations Maitri and Bharati having respective geographic coordinates 70.75°S, 11.67°E, and 69.4°S, 76.17°E. A very stable diurnal variation of the signal has been obtained from both the stations. We reproduced the signal variations of VLF signal using solar zenith angle model coupled with long wavelength propagation capability (LWPC) code. We divided the whole path into several segments and computed the solar zenith angle ( χ ) profile. We assumed a linear relationship between the Wait's exponential model parameters effective reflection height ( h ′ ), steepness parameter ( β ), and solar zenith angle. Theh ′and β values were later used in the LWPC code to obtain the VLF signal amplitude at a particular time. The same procedure was repeated to obtain the whole day signal. Nature of the whole day signal variation from the theoretical modeling is also found to match with our observation to some extent.