NOPR Collection:

Design, constructional aspects and first results of a solar radio spectrograph

Thu, 01 Feb 1996 00:00:00 GMT

Title: Design, constructional aspects and first results of a solar radio spectrograph Authors: Shanmugaraju, A; Umapathy, S Abstract: A solar radio spectrograph (SRS), constructed at our School of Physics to study the dynamic activities of the sun, is described. It consists of the following four parts: (i) antenna system, (ii) analog receiver system, (iii) control system, and (iv) data acquisition and recording system. The antenna system is a log periodic array with 8 dB gain and bandwidth of 50 MHz. The receiver system is a double stage superheterodyne receiver with a overall gain and bandwidth of 50 MHz. The receiver system is a double stage superheterodyne receiver with a overall gain of 80 dB. The control system consists of IEEE 488 GPIB card and a PC to control the sweeping frequency synthesizer which is acting as one of the local oscillator in the receiver. The data acquisition and recording system include a hi-speed data acquisition card and a PC for acquiring the observed data and recording the same for the reproduction of the spectra. The spectrograph is acquiring observational data on solar radio bursts in the bandwidth of 30-80 MHz, which is quite important for understanding the physics of flares and bursts. Its calibration and reproduction of the observed results using it are also described. Page(s): 53-60

Multi-wavelength optical imaging of ionospheric plasma depletions

Thu, 01 Feb 1996 00:00:00 GMT

Title: Multi-wavelength optical imaging of ionospheric plasma depletions Authors: Sinha, H S S; Misra, R N; Chandra, H; Raizada, Shikha; Dutt, N; Vyas, G D Abstract: An all sky optical imaging system using a high gain image intensifier has been built to study a class of equatorial spread-F irregularities which are known as plasma depletions. The 630 nm and 777.4 nm nightglow emission lines, which come essentially from regions about 50 km below the F2-peak and F2-peak respectively, are used to study the plasma depletions when they are located at these altitudes. The newly developed optical imaging system and a VHF Scintillation receiver were operated along with the digital ionosonde from SHAR, India (14°N, 80°N, dip 14°N), during February 1993. Preliminary results are presented here to demonstrate the system capabilities for studying ionospheric plasma depletions. Page(s): 44-52

Day-to-day variability of ionospheric current system

Thu, 01 Feb 1996 00:00:00 GMT

Title: Day-to-day variability of ionospheric current system Authors: James, M E; Tripathi, D; Rastogi, R G Abstract: Day-to-day variability in the solar daily range of the horizontal component of the geomagnetic field (H) over a unique network of thirteen stations extending from 0° to 60° dip latitude within a narrow longitude belt along with the Indo-USSR sector has been studied. The interrelationships of H between each pair of stations in the network are computed. It has been shown that the correlation of H at an equatorial station, Trivandrum, with H at other stations decreases with increasing latitude, becomes almost zero around 25° lat., negative around 35° lat. and again becomes nearly zero at stations north of the S_q focus latitude. This phenomenon has been suggested to be the resultant of the superimposition of lunar semi-diurnal variations over the solar diurnal (S_q) variations of H. Three partially independent regions of current systems have been identified as (i) equatorial regions (ii) low latitudes equatorward of S_q focus and (iii) middle latitudes north of S_q focus. The daily variations of H at latitudes from 30° to 60° are greatly affected by the superimposition of low latitude S_q and higher latitude current systems, giving rise to a significant minimum of H in the forenoon and a maximum in the afternoon hours at stations on either side of the S_q focus. Page(s): 36-43

Longitudinal inequalities in equatorial ionosphere electric field

Thu, 01 Feb 1996 00:00:00 GMT

Title: Longitudinal inequalities in equatorial ionosphere electric field Authors: Rastogi, R G; James, M E; Tripathi, D Abstract: The daily, seasonal and solar cycle variations of the horizontal component of geomagnetic field (H) show significant difference over equatorial stations in the Indian and the American sectors. The electric field parameter H/N_mE [obtained by normalizing H by the peak electron density in the E region (N_mE)] increased by 15% over the Indian sector and by 26% over the American sector from minimum to maximum solar activity years. Seasonal variation of the electric field parameters show significant equinoxial maxima in both the Indian as well as the American sectors. Daily variation of H/N_mE in the American sector has shown an asymmetry in electric field with respect to noon, with significant larger values in the forenoon than in the afternoon hours. Values of H over American stations show a continuous increase with time during the post-midnight hours leading to a significant positive value of H at sunrise Page(s): 27-35