Modeling of the lower ionospheric response and VLF signal modulation during a total solar eclipse using ionospheric chemistry and LWPC
Abstract
The Earth is enveloped by a zone of ionized plasma known as the ionosphere that protects us from the outside hostile environment caused by several solar and extra-terrestrial phenomena. Solar eclipse is one such perturbing agent that exhibits a unique feature of controlled diminution and regain of the incoming solar radiation due to partial or total blocking of the Sun by the lunar disc for a definite period of time. It also provides an excellent opportunity to study such effects as we get to know its time of occurrence much prior to the actual event and thus can prepare ourselves accordingly. One such event (Total Solar Eclipse) took place in the Indian subcontinent on July 22, 2009. Indian Centre for Space Physics (ICSP) conducted a week long campaign to record Very Low Frequency (VLF) data transmitted from the VTX transmitter (18.2 kHz) before, during and after the eclipse from more than a dozen places. All the locations exhibited shifts in the received signal amplitude, either positive or negative depending on the propagation path-length. The interpretation of such effects on VLF signals require a better understanding of the D region ion chemistry which is not available till date. This paper is intended to use our previous knowledge of some of the parameters and explain the observations. We start from calculating the obscuration function and determination of the variation of ionizing radiation during the eclipse period. This information is then used in calculating the rate of ionization. We then incorporate a D-region ion chemistry model to determine the height profile of electron density. These electron densities are then used in the Long Wavelength Propagation Capability (LWPC) code to find the VLF signal modulations. In this process, we have been successful in two ways. First, we have been able to reproduce the trend of signal variation (both positive and negative) from a pure theoretical approach and second, we have been able to improve our knowledge of some of the D-region ion-chemistry parameters.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.560C