NOPR Collection:

Accurate on-line frequency calibration of a rubidium standard using INSAT STFS broadcast in differential mode

2016-10-04T08:38:18Z

Title: Accurate on-line frequency calibration of a rubidium standard using INSAT STFS broadcast in differential mode Authors: Gupta, A Sen; Das, S; Mathur, B S Abstract: The Standard Time and Frequency Signal (STFS) broadcast via INSAT has been used to provide online frequency calibration traceable to the National Physical Laboratory (NPL, New Delhi. The method consists of tracking the phase of the received STFS relative to the local frequency standard. The slope of this phase variation gives the frequency offset. The actual experimental data used in this study consist of those collected simultaneously at the ERTL (East), Calcutta and at NPL. Although, individual data have sinusoidal diurnal residual errors due to satellite position prediction inaccuracy, these are mostly common mode errors that cancel in the differential mode, leading to the present high accuracy of frequency calibration of the order of a few parts in 10¹² over a measurement period of few days. Page(s): 228-236

Solar wind interaction with Mars

2016-10-04T08:36:22Z

Title: Solar wind interaction with Mars Authors: Mohan, Mahandra Abstract: The existence of intrinsic magnetic field at Mars is still a subject of debate. The ionospheric thermal pressure above 300 km is insufficient by itself to withstand the solar wind dynamic pressure, suggesting the presence of magnetic filed ionosphere of Mars which can either be a weak intrinsic magnetic field or an induced magnetic field driven by solar wind interaction with Mars. The photodynamical model of Mahajan and Mayr [J Geophys Res (USA), 95 (1990) 8265] for the case of magnetic field induced by solar plus ion loss via horizontal convection has been studied. It has been found that the induced magnetic field does not affect or alter the photodynamical nature of ionosphere of Mars. Page(s): 224-227

Initial results of whistler observations at Agra using modified experimental set up

2016-10-04T08:34:39Z

Title: Initial results of whistler observations at Agra using modified experimental set up Authors: Singh, Birbal; Singh, Raghuraj; Singh, Rajvir Abstract: Whistler observations have been carried out at a low latitude ground station Agra (geomag. Lat. 17°1´N), during the period 10 Oct. 1995 to 30 April 1996 under the All India Coordinated Programme of Ionospheric Thermospheric Studies (AICPITS)-Phase II, using a modified version of the existing experimental set up. Large whistler activities have been recorded with the new experimental set 9up as compared to those recorded earlier with the old set up under the AICPITS-Phase I period of 1989-92—the reason for this increase is the measurement of two magnetic field components of the incident whistlers by the loop antennas of the new set up which are practically less affected by background noises as compared to the vertical electric field component only recorded by the vertical antenna of the old set up. The data recorded include some unusual whistlers and VLF emissions recorded for the first time in a low latitude ground station. The details of the experimental set up are given and the observed characteristics of some of the whistlers and VLF emissions are discussed. Page(s): 218-223

Magnetic activity dependence of vertical plasma drift and its influence on spread-F

2016-10-04T07:33:30Z

Title: Magnetic activity dependence of vertical plasma drift and its influence on spread-F Authors: Joymon, D; Sebastian, Somi; George, T M; Nayar, S R Prabhakaran Abstract: The HF Doppler radar observations of vertical plasma drift during 1994-95 have been analyzed to study the magnetic activity dependence of vertical plasma drift and its influence on the occurrence of equatorial spread-F (ESF). It is observed that the vertical plasma drift pattern does not show any significant magnetic activity dependence. By analyzing the percentage occurrence of ESF is it also observed that magnetic activity is not a significant factor in deciding the onset of spread-F during the period of study. The occurrence pattern of EST shows strong seasonal dependence with a summer minimum. Page(s): 213-217