NOPR Collection:

Study of VLP Attenuation as a Function of Azimuth Using Atmospherics

2016-11-09T06:18:39Z

Title: Study of VLP Attenuation as a Function of Azimuth Using Atmospherics Authors: Gopalakrishna, S; Sitaramaswamy, P Abstract: From a spectral study of atmospherics received from different azimuth angles, attenuation rates between 5 and 11 kHz have been determined by trial and error method using Wait's equation [Proc. IRE, 4S (1957), 760; 768]. These values are compared with the values obtained by spectral amplitude ratio (SAR) graphs. The values of Ώ at various angles of azimuth for Waltair have been calculated. Using these values of Ώ the attenuation rates from 5 to 11 kHz have been obtained from the theoretical values of Harth [NRL Rep. No. 7763 1974, 147]. The results are found to be in agreement with the available data. Further, the non-reciprocity of VLF waves travelling along east-west and west-east has been proved. Page(s): 112-116

Collisions & Transport of Electrons in the Ionosphere

2016-11-09T06:16:11Z

Title: Collisions & Transport of Electrons in the Ionosphere Authors: Aggarwal, K M; Setty, C S G K Abstract: Analytic expressions are given for the temperature dependent monoenergetic (v_mln) and the two averaged (/n and v/n) collision frequencies for the electron impact with N₂, O₂, N, O, He, Ne, Ar and H in the electron temperature range 100-5000K. These expressions are based on recent experimental and reliable theoretical models of momentum transfer cross-sections for the target gases. Using the latest and reliable atmospheric and ionospheric models for the densities and temperatures of neutral and ionic gas targets, the electron collision frequency <v_g> has been estimated in the upper region of the ionosphere (100-500km). It is observed that at altitudes above 140km, <v_g> values are highest in the winter and lowest in the summer for high solar activity. However, for low solar activity, there is no such change in <v_g>. A study of various electron transport properties shows that their behaviour is opposite to that of <v_g> as expected. Page(s): 105-111

Effect of Lower Ionosphere on the Propagation of VLP Waves at Low Latitudes

2016-11-09T06:13:52Z

Title: Effect of Lower Ionosphere on the Propagation of VLP Waves at Low Latitudes Authors: Singh, D P; Singh, Birbal Abstract: Full wave technique is employed to determine the Budden's reflection coefficients and polarization for VLF waves of frequency 5 kHz propagating in the lower region of the ionosphere at low latitudes. The results are then utilized to determine the propagation losses suffered by the waves in the ionosphere and at different hops of propagation in the earth-ionosphere waveguide. The daytime losses are found to be much higher than nighttime losses. By utilizing the nighttime losses, the possibility of earth-ionosphere waveguide mode propagation for VLF emissions observed at two low latitude ground stations of Moshiri and Hiraiso is examined. Page(s): 101-104

Microwave Line-of-sight Link-Tornado Effect

2016-11-09T06:12:50Z

Title: Microwave Line-of-sight Link-Tornado Effect Authors: Ramakrishna, M; Banerjee, P K; Sarkar, S K; Dutta, H N Abstract: The general signal strength prediction methods in tropospheric propagation mode with the statistical knowledge of conventional radiosonde data are inadequate to explain the microwave signal behavior during a localized phenomenon like tornado. The tornado that struck North Delhi on 17 Mar. 1978, severely affected the microwave line-of-sight link. A study of the signal behaviour during and after the event is reported. Page(s): 97-100