NOPR Collection:

Power Spectra of Equatorial Ionospheric Scintillation at 327 MHz

Mon, 01 Aug 1983 00:00:00 GMT

Title: Power Spectra of Equatorial Ionospheric Scintillation at 327 MHz Authors: Pasricha, P K; Reddy, B M Abstract: Power spectrum analysis of ionospheric scintillation at the equatorial station Ootacamund (Ooty, 3.4ᵒN dip) using the Ooty radio telescope (at 327 MHz) is presented. All the examined power spectra show power-law high-frequency fall-off; Fresnel oscillations are never detected. The representative nighttime spectral features observed at Ooty at 327 M Hz are given as: Fresnel frequency ~ 0.1 Hz, cut-off frequency ~ 0.3 Hz, and spectral slope ~ 4. A decrease in Fresnel frequency is observed at relatively large pairs of dip and zenith angles, thereby implying anisotropic 'sheet' irregularities in the magnetic meridian. The quasi-theoretical approach of spectral analysis is shown to be limited in its application in the deduction of drift speed and scale size of scintillation-causative irregularities under such geometric propagational conditions. Page(s): 136-140

Correlation of Equatorial Ionospheric Scintillation at 327 MHz over 3.2 km

Mon, 01 Aug 1983 00:00:00 GMT

Title: Correlation of Equatorial Ionospheric Scintillation at 327 MHz over 3.2 km Authors: Pasricha, P K; Reddy, B M Abstract: Correlation studies of nighttime ionospheric scintillations at Ootacamund (Ooty. 3.4^ᵒN dip) at 327 M Hz using the Ooty radio telescope and a 13.5-m dish over a rather large east-west base line 3.2 km yielded the pattern drift speed ( ~80 m sec^-1 in the west-to-cast direction) and the scale size ( ~ 250 m) The measured drift speed and scale size are considered with respect to zenith angle of observations. The experimentally determined values of drift speed and scale size are compared with the ones deduced through power spectrum analysis of scintillation fading. The significance of the derived scale size relative to the separation of the receivers is discussed with regard to such drift-measurement techniques. Page(s): 129-135

On the Major Solar Flare Activity in Solar Cycles 19, 20 & 21 (1955-79)

Mon, 01 Aug 1983 00:00:00 GMT

Title: On the Major Solar Flare Activity in Solar Cycles 19, 20 & 21 (1955-79) Authors: Badruddin; Yadav, R S; Yadav, N R Abstract: Utilizing the major solar flare data for the period 1955-79, which includes solar cycles 19, 20 and 21, a comprehensive analysis of these flares is presented. In this analysis, study is made of their distribution around the sun. both in latitude and longitude, the time latitude occurrence in solar cycles 19, 20 and 21 and their nature and frequency in northern and southern hemispheres in these solar cycles. and the change of occurrence of these flares in the course of years for both halves of the solar disk separately and also for the disk as a whole. Their relationship with sunspot numbers in different solar cycles and their occurrence frequency with increasing comprehensive flare index in general and for cycles 19 and 20 in particular (observations for cycle 21 are not complete) have also been studied. Page(s): 124-128

A Prediction Model for Equatorial & Low Latitude HF Communication Parameters during Magnetic Disturbances

Mon, 01 Aug 1983 00:00:00 GMT

Title: A Prediction Model for Equatorial & Low Latitude HF Communication Parameters during Magnetic Disturbances Authors: Lakshmi, Dr; Reddy, B M; Shastri, S Abstract: A prediction model for equatorial and low latitude disturbed time ionosphere has been evolved using a large data base to aid in short-term forecasting of HF communication parameters. The variety of solar and geophysical data that is available on near-real time basi, at the Associate Regional Warning Centre being operated from National Physical Laboratory. New Delhi, enables the prediction of magnetic activity levels with some accuracy. The present model will facilitate the HF link operators to correct their predicted circuit parameters for any short-term deviations produced by magnetic storms. This study has shown that deviation in maximum usable frequencies during magnetically disturbed days exhibit rather complex behaviour in certain latitude zones: and the possible actions which a communicator can take to improve the reliability of HF circuits operating through reflections in this zone are suggested. Page(s): 118-123