http://nopr.niscpr.res.in/handle/123456789/37375 2026-10-09T21:54:05Z http://nopr.niscpr.res.in/handle/123456789/37610 Title: Nocturnal Variation of Total Absorption & Nighttime E-Region Authors: Jain, S L; Rai, R K Abstract: The results of a study on ionospheric absorption during night hours at Udaipur (23^o 35'N) are presented. In the nocturnal variation of the total absorption, a dip is observed during twilight hours. The higher value of absorption observed during the night hours as compared to that during twilight hours is attributed to ionization in the E-region caused by geocoronal Lyman-β and Lyman-ɑ. The electron density at the peak of the nighttime E-region is estimated to be of the order of 104 electron/cm³. Page(s): 263-264 1976-09-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/37609 Title: Latitude Variation of Peak E, Occurrences during a Half-Solar Cycle Authors: Rao, S P Manohar; Rao, B Ramachandra Abstract: The results of the variation of the peak occurrence (evaluated as percentage) of sporadic-E during an ascending half-solar cycle with geomagnetic latitude are reported. It is seen that E_s occurrence is maximum in low sunspot period for low and middle latitudes, and vice versa for equatorial and high latitudes. The southern latitudes, in particular, show a systematic decrease in E, occurrence with increase in geomagnetic latitude for all limiting frequencies of E_s (<i>f</i>E_s). An attempt is made to explain the above results on the basis of the <i>S_q</i> current system. Page(s): 261-263 1976-09-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/37608 Title: Threshold Height & Equatorial Spread F Authors: Subrahmanyam, V; Rao, M Srirama Abstract: About 300 events of disappearance and subsequent reappearance of spread F at three equatorial stations, Singapore, Bangkok and Ibadan have been examined for the sunspot minimum and maximum years. No systematic changes in the layer height are observed to be associated with these events, showing that no threshold height exists for the spread F irregularities to sustain. Page(s): 259-261 1976-09-01T00:00:00Z http://nopr.niscpr.res.in/handle/123456789/37607 Title: Nocturnal E-region during Meteor Showers Authors: Naidu, J V M; Rao, B Ramachandra Abstract: The effects of Geminid meteor shower of 1972 on nocturnal E-region are studied from If amplitude records. The studies on the peak activity day indicate an enhancement of both ionization and irregularities during the latter part of the night. Also, good correlations are observed between the amplitude attenuation and radio meteor count, and increase in fading rate and visual meteor count. The results indicate that the increase of ionization is the earlier effect and the formation of irregularities is the latter effect. Page(s): 258-259 1976-09-01T00:00:00Z