NOPR Collection:

Equatorial Spread-F Configurations & Geomagnetic Activity

2016-11-23T10:08:50Z

Title: Equatorial Spread-F Configurations & Geomagnetic Activity Authors: Sastry, J Hanumath; Sasidharan, K; Subrahmanyam, V; Rao, M Srirama Abstract: Using quarter-hourly ionogram data at Kodaikanal (geomag. lat : 0·6°N; dip: 3·5°N) for the period 1957-63 a study is made of the effect of geomagnetic activity on the Occurrence of range and frequency types of spread-F. It is found that the occurrence of both range and frequency types of spread-F shows a significant negative correlation with geomagnetic activity but only during years of high sunspot activity. Page(s): 314-316

TEC from Group Delay Measurements near Magnetic Equator (Ootacamund)

2016-11-23T09:42:28Z

Title: TEC from Group Delay Measurements near Magnetic Equator (Ootacamund) Authors: Sethia, G; Chandra, H; Rastogi, R G Abstract: The results of total electron content (TEC), N_T, derived from the group delay measurements made at Ootacamund during ATS-6 phase-II are presented. These results are also compared with the results of ionospheric TEC derived from the Faraday rotation measurements made simultaneously at the same station. The nighttime electron content values obtained from group delay measurements are found to be much higher than the corresponding values obtained from Faraday rotation measurements. The daytime values of N_T are also found to be higher on disturbed days than on quiet days. Page(s): 312-314

Analysis of Fading of Signals from Spread-F Irregularities Observed Simultaneously at different Heights

2016-11-23T09:40:11Z

Title: Analysis of Fading of Signals from Spread-F Irregularities Observed Simultaneously at different Heights Authors: Rao, M Srirama; Subrahmanyam, V Abstract: Simultaneous fading of 2·4 MHz and 5·6 MHz pulsed radio signals from different heights is studied. Analysis of over 150 such records reveals that (i) the characteristic length and the line-of-sight velocity of the irregularities observed on these two frequencies increase with height to a certain extent and thereafter decrease, indicating the presence of vertical wind shear; and (ii) the irregularities observed on 2·4 MHz are larger in size and travel faster than those observed on 5·6 MHz, indicating that probably large size irregularities have greater prevailing drift velocities. Page(s): 311-312

Electron Temperature & Concentration in the Plasmasphere at an Altitude of 3000 km from ISIS-1 Langmuir Probe Measurements

2016-11-23T09:38:26Z

Title: Electron Temperature & Concentration in the Plasmasphere at an Altitude of 3000 km from ISIS-1 Langmuir Probe Measurements Authors: Mahalan, K K; Pandey, V K Abstract: Langmuir probe data from ISIS-I satellite are used to study the latitudinal profiles of electron temperature (T_e) and concentration (N_e) in the plasmasphere at an altitude of 3000 km. The electron temperature reveals minimum values in the equatorial latitudes and indicates appreciable diurnal variation in all seasons, with an average temperature of about 5000^o K during daytime and about 2000^o K during nighttime. The electron temperature starts increasing towards midlatitude and then peaks near plasma trough region attaining an average temperature of more than 5500^o K both during day and night. The electron concentration reveals maximum value in the equatorial latitudes. This equatorial maximum of electron concentration does not show any significant diurnal or seasonal change. There is a large latitudinal gradient in electron concentration near the plasma trough region where it decreases by more than a factor of 6 from its equatorial maximum value. Page(s): 305-310