Modeling of long-path propagation characteristics of VLF radio waves as observed from Indian Antarctic station Maitri
01 Oct 2015-Journal of Geophysical Research (John Wiley & Sons, Ltd)-Vol. 120, Iss: 10, pp 8872-8883
TL;DR: In this paper, the long-distance propagation characteristics of very low frequency (VLF) signals transmitted from VTX (18.2 ) and NWC (19.8 ) transmitters recorded at the Indian permanent station Maitri (latitude 70° 45′S, longitude 114° 40′E) in 2007-2008 were investigated.
Abstract: Propagation of very low frequency (VLF) radio signal through the Earth-ionosphere waveguide depends strongly on the plasma properties of the ionospheric D layer. Solar extreme ultraviolet radiation plays the central role in controlling physical and chemical properties of the lower ionospheric layers and hence determining the propagation characteristics of a VLF signal. The nature of interference among different propagating modes varies widely with the length of the propagation path. For a very long path, exposure of solar radiation and thus the degree of ionization vary by a large amount along the path. This influences the VLF signal profile by modulating the sky wave propagation. To understand the propagation characteristics over such a long path, we need a thorough investigation of the chemical reactions of the lower ionosphere which is lacking in the literature. Study of radio signal characteristics in the Antarctic region during summer period in the Southern Hemisphere gives us a unique opportunity to explore such a possibility. In addition, there is an extra feature in this path—the presence of solar radiation and hence the D region for the whole day during summer in at least some sections of the path. In this paper, we present long-distance propagation characteristics of VLF signals transmitted from VTX (18.2 kHz) and NWC (19.8 kHz) transmitters recorded at the Indian permanent station Maitri (latitude 70° 45′S, longitude 114° 40′E) in 2007–2008. A very stable diurnal variation of the signal has been obtained with no signature of nighttime fluctuation due the presence of 24 h of sunlight. Using ion production and recombination profiles by solar irradiance and incorporating D region ion chemistry processes, we calculate the electron density profile at different heights. Using this profile in the Long Wavelength Propagation Capability code, we are able to reproduce the amplitude of VLF signal.
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TL;DR: In this article, a very stable diurnal variation of very low frequency (VLF) signal has been obtained from both the stations using solar zenith angle model coupled with Long Wavelength Propagation Capability (LWPC) code.
Abstract: Characteristics 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 Center 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. The h′ 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.
13 citations
TL;DR: In this paper, the authors used the electron density profiles based on IRI outcomes during a quiet ionospheric condition, and used the Wait's exponential model with a log-linear fitting of electron density to compute the β and h′ from their fundamental definition.
11 citations
TL;DR: A very low frequency (VLF) wave detection system has been designed at Wuhan University (WHU) and recently deployed by the Polar Research Institute of China at the Chinese Great Wall station (GWS, 62.22°S, 58.96°W) in Antarctica as discussed by the authors .
Abstract: A Very Low Frequency (VLF) wave detection system has been designed at Wuhan University (WHU) and recently deployed by the Polar Research Institute of China at the Chinese Great Wall station (GWS, 62.22°S, 58.96°W) in Antarctica. With a dynamic range of ∼110 dB and timing accuracy of ∼100 ns, this detection system can provide observational data with a resolution that can facilitate space physics and space weather studies. This paper presents the first results of the wave measurements by the WHU VLF wave detection system at GWS to verify the performance of the system. With the routine operation for 3 months, the system can acquire the dynamic changes of the wave amplitudes and phases of various ground-based VLF transmitter signals emitted in both North America and Europe. A preliminary analysis indicates that the properties of the VLF transmitter signals observed at GWS during the X-class solar flare events are consistent with previous studies. As the HWU-GWS path crosses the South Atlantic Anomaly region, the observations also imply a good connection in space and time between the VLF wave disturbances and the lower ionosphere variation potentially caused by magnetospheric electron precipitation during the geomagnetic storm period. It is therefore well expected that the acquisition of VLF wave data at GWS, in combination with datasets from other instruments, can be beneficial for space weather studies related to the radiation belt dynamics, terrestrial lightning discharge, whistler wave propagation, and the lower ionosphere disturbance, etc., in the polar region.
4 citations
DOI•
26 Aug 2022
TL;DR: A very low frequency (VLF) wave detection system has been designed at Wuhan University (WHU) and recently deployed by the Polar Research Institute of China at the Chinese Great Wall station (GWS, 62.22°S, 58.96°W) in Antarctica as discussed by the authors .
Abstract: A Very Low Frequency (VLF) wave detection system has been designed at Wuhan University (WHU) and recently deployed by the Polar Research Institute of China at the Chinese Great Wall station (GWS, 62.22°S, 58.96°W) in Antarctica. With a dynamic range of ∼110 dB and timing accuracy of ∼100 ns, this detection system can provide observational data with a resolution that can facilitate space physics and space weather studies. This paper presents the first results of the wave measurements by the WHU VLF wave detection system at GWS to verify the performance of the system. With the routine operation for 3 months, the system can acquire the dynamic changes of the wave amplitudes and phases of various ground‐based VLF transmitter signals emitted in both North America and Europe. A preliminary analysis indicates that the properties of the VLF transmitter signals observed at GWS during the X‐class solar flare events are consistent with previous studies. As the HWU‐GWS path crosses the South Atlantic Anomaly region, the observations also imply a good connection in space and time between the VLF wave disturbances and the lower ionosphere variation potentially caused by magnetospheric electron precipitation during the geomagnetic storm period. It is therefore well expected that the acquisition of VLF wave data at GWS, in combination with datasets from other instruments, can be beneficial for space weather studies related to the radiation belt dynamics, terrestrial lightning discharge, whistler wave propagation, and the lower ionosphere disturbance, etc., in the polar region.
2 citations
2 citations
References
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06 Oct 2018
483 citations
TL;DR: In this paper, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals, for various dates exhibiting notably different levels of solar activity.
Abstract: Increases in the solar ultraviolet flux (wavelengths shorter than 1250A) over the past five years of rising solar activity have been larger than anticipated. This increase in UV flux dramatically affects the production of ionization of the various constituents in the thermosphere. Measurements of the solar UV flux by the Atmosphere Explorer satellites are used to determine ionization frequencies for the major thermospheric species for various dates exhibiting notably different levels of solar activity. For the convenience of users of such data, a reduced set of cross-section and flux data is presented for the wavelength range below 1027A, consisting of 37 wavelength intervals
341 citations
TL;DR: The negative ion to electron ratio is important below 70 km and affects the electron distribution below that altitude as mentioned in this paper, and the behavior of the ionization is related to the formation of the E layer.
Abstract: Radiations of solar origin penetrating below 85 km in the terrestrial atmosphere are: (1) X rays of λ<10 A; (2) Lyman α; and (3) wavelengths greater than 1800 A. These radiations can ionize: (1) molecular nitrogen and oxygen; (2) nitric oxide; and (3) various atoms such as sodium and calcium. Molecular oxygen and nitrogen are also ionized by cosmic rays. The negative ion to electron ratio is important below 70 km and affects the electron distribution below that altitude. It is possible to explain normal conditions of ionization by cosmic rays and Lyman α. Conditions due to solar flares must be explained by X rays. Above 85 km, the behavior of the ionization is related to the formation of the E layer.
270 citations
TL;DR: The International Reference Ionosphere (1978) as discussed by the authors is the most widely used reference ionospheric data set, which includes electron density, electron and ion temperature, and (positive) ion composition.
Abstract: Under the supervision of an international steering committee, basic data for establishing ionospheric profiles were gathered, critically reviewed, and used for establishing vertical profiles of the most important parameters of the ionosphere, namely, electron density, electron and ion temperature, and (positive) ion composition. The data sources used are described in detail, their reliability and coverage is discussed, and remaining problems are reviewed. The International Reference Ionosphere (1978) is to be published soon by URSI in the form of computer programs.
228 citations