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Radiation Efficiency of Some Satellite Aerials in an Ionized Medium

Fri, 01 Dec 1972 00:00:00 GMT

Title: Radiation Efficiency of Some Satellite Aerials in an Ionized Medium Authors: Gupta, R. K. Abstract: Using linearized hydrodynamic theory and appropriate current distribution, radiation efficiencies of a dipole, a turnstile, a comer driven square loop and an Alford aerial immersed in an isotropic ionized media are compared at various plasma frequencies. It is found that the radiation efficiency of all the aerials except that of the Alford aerial decreases rapidly With increase in plasma frequency. The efficiency of the Alford aerial is very high and remains almost constant at all plasma frequencies. It is concluded that the Alford aerial is a better aerial for working in the ionized medium and its deployment on Indian satellites for ionospheric research purposes is suggested. Page(s): 281-285

Unusual Multiflash Whistlers at Low Latitudes

Fri, 01 Dec 1972 00:00:00 GMT

Title: Unusual Multiflash Whistlers at Low Latitudes Authors: Singh, Birbal; Tantry, B. A. P. Abstract: Employing Haselgrove equations and a diffusive equilibrium model of the ionosphere, ray-tracing computations are carried out to explain the propagation characteristics of unusual type of multiflash whistlers recorded in the course of routine observations at low latitude whistler ground station, Nainital. The origin of these whistlers is explained in the following manner. They are caused by electromagnetic waves which are radiated from three successive return strokes of a lightning discharge or from the return strokes of three different lightning discharges occurring within 70 msec at slightly different places. These waves then penetrate the ionosphere at three different entry points and propagate towards opposite hemisphere in the whistler mode. Ultimately, they are received at the ground; giving rise to three peculiar whistler traces with different lower and upper cutoff frequencies which are explained in terms of the deviation of their ray paths from their respective whistler bunches. Page(s): 277-280

Effect of Horizontal Gradients on the Propagation of Whistlers at Low Latitudes

Fri, 01 Dec 1972 00:00:00 GMT

Title: Effect of Horizontal Gradients on the Propagation of Whistlers at Low Latitudes Authors: Singh, Birbal; Tantry, B. A. P. Abstract: The possibilities of recordinl1. at ground stations, the unusual type of whistlers observed at low latitude ground stations, Gulmarg (geomag. lat., 24°10'N) and Nainital (geomaj lat., 19°1'N), India, are discussed. It is shown from the ray-tracing computations that a, small but suitable negative latitudinal I1radient of electron, density in the night-time, ionosphere at low latitudes is mainly responsible for non-ducted unusual type of whistlers to be observed on the ground. The propagation characteristics, including the upper and lower cut of frequencies of the low latitude whistlers observed on the ground, are also explained in terms of a P-L mode of propagation assuming a small negative latitudinal gradient of electron density in the ionosphere at low latitudes. Page(s): 273-276

Total Electron Content Measurements over Kurukshetra

Fri, 01 Dec 1972 00:00:00 GMT

Title: Total Electron Content Measurements over Kurukshetra Authors: Prakash, Sant; Lal, J. B. Abstract: An analysis has been made of the result of total electron content of the ionosphere (I) derived from faraday rotation measurements of 40 MHz satellite (S-66) signals at Kurukshetra (lat.29.9^ᵒ N, long. 76.8^ᵒ E, dip 45.6^ᵒ) for the period June 1968-April 1969. Day-to-day variation, seasonal anomaly and semi-annual effect have been observed in the electron content at this station. During daytime I has always been found to increase towards the south and decrease towards the north of Kurukshetra but during night-time I has, at times, been found to increase towards' north of Kurukshetra, although no unusual magnetic activity has been reported on such occasions: This may be due to larger influx of ionization on such occasions from the upper atmosphere. Page(s): 269-272