Meteorological effect on long distant 40 kHz signal

et al. 2015

JGR Space Physics

The present work investigates the effects of long-duration geomagnetic storms on VLF signal during ionospheric sunrise time, commonly known as D Layer Preparation Time (DLPT) depth. The VLF signal at 19.8 kHz transmitted from Northwest Cape, Australia, and received at a low-latitude station, Tripura, India, is used for the present analysis. The data for the analysis are selected from November 2008 to October 2011. In the active period of the geomagnetic storms, the average DLPT depth is found to have a negative correlation coefficient of 0.91 with geomagnetic Ap index. It is also found that with each 10 unit increase of Ap index, the DLPT depth (the day and night asymmetry level) changes by 1.25 dB. The results are supported with modeled International Reference Ionosphere (IRI) electron density data and DLPT depth at 71 km height for the three positions, namely, receiver position, signal hop position, and the transmitter position along the total Great Circle Path. It is found that the receiver position electron density is the main controlling factor for DLPT depth. The correlation between IRI electron density and DLPT depth increases from À0.13 at transmitter position to À0.33 at the first hop position, to À0.46 at the receiver position, respectively. The percentage change of post storm electron density, at 71 km height, is found to increase by more than 100% at the receiver position. The results are discussed on the basis of the electron density changes over the signal propagation path, mainly caused by the geomagnetic storms.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Long‐duration geomagnetic storm effects on the D region of the ionosphere: Some case studies using VLF signal

Choudhury

et al. 2015

JGR Space Physics

“…The Low Frequency (LF) radio wave travels round the earth via wave guide formed by the earth and lower surface of ionosphere. Ionospheric parameters such as electron density and collision frequency remaining constant, the propagation is dependent on cloud coverage, humidity and temperature [1]. The variation of attenuation of low frequency due to variation of tropospheric condition is so far neglected.…”

Section: Introductionmentioning

confidence: 99%

Variation of 40 kHz Signal Level in Relation to Sunrise, Sunset and Climatic Condition

AIP Conference Proceedings

Saha

et al. 2007

Self Cite

The sunrise effect, sunset effect, the diurnal and seasonal variations are the characteristic feature of low frequency (LF) radio wave propagated over a large distance. The normal character has been found to be perturbed during rainy days. The amplitude of 40 kHz signal transmitted from Miyakoji station, Japan and received in North-East India is remarkably attenuated after the commencement of rain. On the basis of nature of attenuation the observed records have been classified into two different forms viz., F1 and F2. An analysis in this regard is represented in this paper.

“…VLF/LF natural and navigational signals studied from our location (23.75 0 N, 91.25 0 E) have already reported various solar terrestrial events like geomagnetic storms, solar eclipse, meteor showers, thunderstorms, etc. [9,17,18,19,20,21].…”

mentioning

confidence: 99%

Sunrise effect on 40 kHz signal amplitude and its characteristic variation with respect to geomagnetic storms

Saha

2015

Can. J. Phys.

The sunrise effect is a characteristic feature of Very Low Frequency (VLF) and Low Frequency (LF) radio waves propagated over a large distance. The 40 kHz signal level, transmitted from Miyakoji station (37.4 0 N, 140.9 0 E), Japan and received at Tripura University (23 0 N, 91.4 0 E), is found to be attenuated during sunrise with an enhancement before the decrease in the signal level. On the basis of nature of attenuation of the observed records from 2005 to 2006, those are classified into four different types viz, Type A (three step attenuation), Type B (two step attenuation), Type C (one step attenuation) and Type D (no attenuation). 84% of Type D cases and 31% of Type C cases are observed during geomagnetically active days whereas only 0.9% of Type A cases and 07% of Type B cases are observed during geomagnetically active days. The fade amplitude of Type C fade is also found to maintain a good negative correlation of 77.3 % with the geomagnetic A p indices over the period of two years. From the model calculation it is found that in the altitude range from 65 to 80 km, on an average the electron density increases by a factor of 5.22 times during geomagnetically active days than that during normal days.