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Propagation Characteristics of hf Signal over a Transequatorial Path

2016-11-28T10:27:06Z

Title: Propagation Characteristics of hf Signal over a Transequatorial Path Authors: Sen, A.K.; Trehan, S.K. Abstract: The propagation characteristics of an hf radio signal (21.485 MHz, Radio Australia) over a transequatorial path viz. from Melbourne (37.5°8; 144.59°S) to Calcutta have been studied experimentally. A morning maximum is seen to occur in many cases. Page(s): 334

Long Period Waves in the Upper Troposphere & Lower Stratosphere over the Indian Region

2016-11-28T10:25:41Z

Title: Long Period Waves in the Upper Troposphere & Lower Stratosphere over the Indian Region Authors: Rao, K. S. Raja; Thapliyal, V.; Patil, S. R. Abstract: Long period waves in the upper troposphere and lower stratosphere in the Indian region have been identified using monthly mean data on the zonal and meridional winds and temperature over seven stations in the latitude range of 8-28°N. Four members of the wave family, viz. 2 month, 6 month, 12 month and 20-40 month periodicities, have been identified. The 2 month wave is masked by the more dominant Kelvin wave. The 6 month wave is confined to the equatorial stratosphere. The tilt of the line of maximum amplitude suggests transport of energy from the upper troposphere to lower stratosphere. The amplitude of the annual wave is a maximum below the tropopause. The prominent maximum near 200 mb, between 20 and 25°N is associated with the subtropical westerly jet. The quasi-biennial oscillation (QBO) present in the zonal wind and temperature is confined to 3D-month period. From the downward tilt from the equator to the sub-tropics in the line of maximum amplitude, it is inferred that the QBO originates in the equatorial stratosphere and travels to the upper troposphere over the subtropical latitudes. Page(s): 328-334

Satellite Tracking Systems

2016-11-28T10:24:12Z

Title: Satellite Tracking Systems Authors: Saha, M. K.; Kalyanaraman, S. Abstract: Satellite tracking systems which will provide range, range rate and angular information are being developed. The basic systems are Interferometry, Doppler and Tone Ranging. Data from these will be used to generate satellite ephemeris. Interferometry system uses two pairs of antennas each for north-south and east-west directions, providing coarse and fine data for direction cosines. The coarse data are used to resolve the ambiguity in the fine channel which provides the accuracy of approximately ±6'. Doppler system tracks the carrier frequency of the on-board telemetry transmitter with a tracking filter using phase-lock loop, to provide accuracy in radial velocity measurement within 10m/ sec. Tone ranging system uses four tones which are received in the satellite and retransmitted. The transmitted and received tones are processed in the ground to extract range data. This provides an accuracy of ± 375m and a maximum range capability of nearly 5000 km. Page(s): 323-327

Prediction of the Occurrence of Sporadic E in the Indian Subcontinent

2016-11-28T10:22:56Z

Title: Prediction of the Occurrence of Sporadic E in the Indian Subcontinent Authors: Saksena, R. C. Abstract: The contour diagrams (latitude versus time) for the occurrence of sporadic E have been drawn from the f₀ Esdata from Indian stations and from Bangkok, Thailand (a neighbouring country). This has been done separately for equatorial and temperate latitudes during high and low solar activity. The Phillips' rule, which states that a straight line will fit a sporadic E cumulative distribution, appears to hold good only beyond the most probable f₀ Esvalue for all latitudes. The contour diagrams of the gradient of these straight lines have been drawn. These two sets of contours, with the help of Phillips' rule, could be used for predicting the percentage occurrence of sporadic E above any specific value of f₀ Es for any latitude, at any time of the day and for high and low solar activity. Page(s): 318-322