NOPR Collection:

Effects of Gravity Waves on Eclipse Time Absorption of Radio Waves

2016-11-04T09:19:15Z

Title: Effects of Gravity Waves on Eclipse Time Absorption of Radio Waves Authors: Devi, Minakshi; Barbara, A K; Talukdar, P Abstract: Ionograms and amplitude measurements at 2.7 MHz were taken during the solar eclipse of 16 Feb 1980 at Gauhati University. Abnormally low absorption observed during the maximum eclipse effect condition has been linked with formation of distortions or curvatures in the reflecting surface produced by gravity waves generated during eclipse. The wavy variation pattern of f_oF2, f_oF1, etc. seen at this station supports the theories of formation of such waves. The amplitudes of undulations in f_oF1 and f_min have been found to increase when that of f_oF2 is decreased. Along with this the ionization density of F1-layer is also lowered when that of F2-layer is increased. The amplitudes of undulations and ionization densities of F1 and F2-layers suggest the migration of ionization from lower to upper layers and the presence of gravity waves. Page(s): 42-44

Rate Coefficients of Some Important Interstellar lon-Neutral Reactions

2016-11-04T09:13:40Z

Title: Rate Coefficients of Some Important Interstellar lon-Neutral Reactions Authors: Ghosh, S N; Ghosh, K K Abstract: Unlike neutral-neutral reactions which are mainly endothermic, most of the ion-neutral reactions in the interstellar space are exothermic. The energy released by the reaction of the latter type is less than the dissociation energy of the molecule. Such reactions may play dominant role in the interstellar medium. The information regarding the rate coefficients of polyatomic ionneutral reactions is meagre. A semi-classical approach is adopted here for calculating rate coefficient and its temperature dependence. The coefficients of certain important ion-neutral reactions in the interstellar medium are calculated and presented. Page(s): 40-41

Sudden Decrease of Sweeper Activity during Solar Flares

2016-11-04T09:12:23Z

Title: Sudden Decrease of Sweeper Activity during Solar Flares Authors: Sen, A K; Trehan, S K; Dey, S Shekhar Abstract: A peculiar transionospheric radio noise called sweepers which undergoes a diurnal and seasonal dependence presumably of ionospheric origin has been observed in Calcutta. During the last solar eclipse of 16 Feb 1980 over the Indian subcontinent a remarkable enhancement of sweeper activity was seen associated with the eclipse phenomena. This was believed to be due to the reduced transionospheric absorption at such times. The recent observations prompted us to explore if any change of the activity is noticeable during a sudden ionospheric disturbance (SID) and some convincing results are obtained. Page(s): 38-39

Post-Sunset Behaviour of the Equatorial Anomaly in the Indian Sector

2016-11-04T09:10:45Z

Title: Post-Sunset Behaviour of the Equatorial Anomaly in the Indian Sector Authors: Sastri, J Hanumath Abstract: A detailed investigation is made of the relationship, in the post-sunset period, between the depth of the equatorial anomaly and the evening rise of F-region at the trough on a day-to-day basis, using published data of ionosonde stations in the Indian sector for a 2-yr period (1957-58) of high sunspot activity. The day-to-day changes in the post-sunset rise of F-region at the trough are found to show a significant positive correlation with those of the depth of the anomaly, and a significant negative correlation with those of f_oF₂ at the trough during all seasons and on quiet as well as disturbed days. The day-to-day variability of f_oF₂ at the crest of the anomaly is also found to exhibit a significant positive correlation (with a delay of 2 hr) with that of the evening rise of F region at the trough during disturbed days of all the three seasons and on quiet days of summer and equinoxes. The results of the present study are in accordance with the prevailing view that the post-sunset enhancement of the anomaly during periods of high sunspot activity is due to a renewal of the 'fountain effect'. It is suggested that the conspicuous absence of a significant relationship of the day-to-day variability of f_oF₂at the crest of the anomaly with that of the post-sunset rise of F region at the trough during quiet days of winter months is due to the effect of poleward neutral winds in the post-sunset period. Page(s): 33-37