http://nopr.niscpr.res.in/handle/123456789/37390 2026-10-10T20:39:43Z http://nopr.niscpr.res.in/handle/123456789/37993 Title: Statistical Analysis of F-Region Echoes in the Presence of Intervening E_s Clouds Authors: Pradhan, S. M.; Singh, B.; Tripathi, A. N.; Tantry, B. A. P. Abstract: The amplitude fading records of F-region echoes in the presence of E_s irregularities show statistical properties common to certain focusing processes in the ionosphere. This result is shown to support indirectly the hypothesis advanced by the authors that the E_s clouds can focus the radio waves, when the reflection is taking place from normal F-region. Page(s): 228-230 1973-09-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/37992 Title: Effect of Ionization Drifts on TID Statistics Authors: Pradhan, S. M.; Singh, I. S.; Singh, B.; Tantry, B. A. P. Abstract: The effect of electromagnetic drifts of the Ionospheric plasma' on the amplitude of travelling ionospheric disturbances (TIDs) induced by gravity waves is studied. It is found that upward lifting of the F-layer causes the amplitude of the TIDs to increase in the evening hours. The other amplitude enhancement occasionally observed in the morning hours is attributed to spatial resonance mechanism, which is discussed in detail. Theoretical calculations show that horizontal drift rather than vertical drift is more important in controlling the diurnal variation of the TIDs at low latitudes by the spatial resonance mechanism. A reasonable agreement between the theoretical calculations and experimental observations is obtained within the limits of the approximations involved in the calculations. Page(s): 224-227 1973-09-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/37991 Title: Winter Anomaly in Ionospheric Absorption of Radio Waves over Half a Sunspot Cycle Authors: Patel, B. M.; Patel, J. C.; Kotadia, K. M. Abstract: The winter anomaly in ionospheric absorption is studied at a mid-latitude station over half a solar cycle. It is shown that the anomalous increases of absorption on some days in winter are better correlated with 10 mb-level geopotential height than with temperature at that level. The anomaly is most marked in the month of January. It was about 168% in 1964 and 79% in 1969. The present results along with those reported by others earlier are evidences to suggest that the possible cause of winter anomaly in ionospheric absorption may be an Increase in ionization In the D and probably in the E regions of the ionosphere following disturbances in the pressure and wind circulation system at stratospheric and mesospheric levels. Page(s): 219-223 1973-09-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/37989 Title: Some Studies on D-Region Electron Density Profiles Authors: Chakrabarty, D.K.; Chakrabarty, Purobi Abstract: Model electron density profiles in the D-region have been prepared for various solar conditions and for mid-latitude and equatorial locations on the basis of production and loss rates of electrons established from the study of a large number of electron density profiles measured under various conditions. It is found that below 8S km, electron density variations follow a linear law of the type <i>q </i> = β <i>N</i>_e<i>, </i> and above this altitude a square law of the type <i>q </i> = ɑ <i>N_e². </i> The electron production rate for any condition of solar activity has been calculated after establishing variations connecting solar activity and solar Lɑ and X-ray intensities in various ranges as obtained from rocket and satellite observations made under various conditions since 1954. Page(s): 211-218 1973-09-01T00:00:00Z