NISCAIR Online Periodicals Repository Collection: IJRSP Vol.37(1) [February 2008]

Equatorial spread-F research in India: A brief review

Tue, 29 Jan 2008 22:58:59 GMT

Title: Equatorial spread-F research in India: A brief review

Authors: Sekar, R; Chakrabarty, D

Abstract: The Equatorial Spread-F (ESF) is a complex phenomenon encompassing a wide range of scale sizes (covering more than six orders of magnitude) of irregularities in electron and ion densities as well as in electric fields. The generation mechanisms involve not only the plasma processes but also neutral processes. Thus, to understand the different facets of ESF manifestations, investigations have been carried out using multiple techniques. The research in this topic has practical implications as these irregularities affect the propagation of radio wave even in Ultra High Frequency band. Considerable amount of works have been done in India to understand this phenomenon. Some of the important results in the last three decades, as perceived by the authors, are reviewed in this paper. This involves results obtained from ground-based, rocket and satellite borne experiments conducted from India along with theoretical and laboratory simulations.

Page(s): 7-27

Influence of coronal mass ejections on global electric circuit

Tue, 29 Jan 2008 22:58:59 GMT

Title: Influence of coronal mass ejections on global electric circuit

Authors: Kumar, C P Anil; Panneerselvam, C; Nair, K U; Jeeva, K; Selvaraj, C; Gurubaran, S; Rajaram, R

Abstract: This paper is concerned with the elucidation of flow of particles and field from the sun into the terrestrial system and their subsequent role in Global Electric Circuit (GEC). Many flare associated Coronal Mass Ejections (CMEs) have been studied from ACE satellite data during the last phase of the 23rd solar cycle. Such solar ejections consist of hot electrons, protons and helium ions embedded in magnetic fields of various intensities and which travel with velocities greater than supersonic speed towards the earth and breach terrestrial magnetic fields (under favourable conditions) and cause geomagnetic storms. Contemporary data of geoelectrical measurements made at the high latitude Indian Antarctic Research Station, Maitri (70.45°S, 11.44°E) have also been used to investigate the electrical processes during, before and after the above events. The study leads to the conclusion that CMEs enhance the population of the multi-ion plasma species, which paves the way for an increase in the overhead ionospheric electric potential during the onset or even up to the main phase of the magnetic disturbance. The near earth electrical environment is besieged with magnetic disturbance at the high latitude.

Page(s): 39-45

Effect of dust particles on two-stream instability: A possible explanation for the persistence of ionization trails of Leonid meteor showers

Tue, 29 Jan 2008 22:58:59 GMT

Title: Effect of dust particles on two-stream instability: A possible explanation for the persistence of ionization trails of Leonid meteor showers

Authors: Kulkarni, V H; Muralikrishna, P

Abstract: Assuming a collisional plasma having dust particles and only electrons are magnetized, the two-stream instability is studied for the excitation of low frequency waves. The production and losses of both ions and electrons are included. In the absence of production, it is shown that losses by attachments of both ions and electrons on dust particles, two-stream instability require the drift velocity greater than ion acoustic velocity. The growth rate is reduced and the wave amplitude at saturation is reduced. Therefore the generation and magnitudes of ionization density irregularities is reduced. It is expected that the cross-field diffusion of ionization due to wave turbulence is affected. It is known that during meteor shower periods the E-region of the ionosphere has a significant number of dust particles. Therefore density irregularities in the ionosphere are modified. Also amplitude dependent diffusion rate is reduced. It is suggested that the presence of dust particles may be a reason for persistence of ionization trails seen for longer periods during Leonid meteor showers

Page(s): 34-38

Cosmic ray anisotropies during the Oct. 28-31, 2003 Halloween event

Tue, 29 Jan 2008 22:58:59 GMT

Title: Cosmic ray anisotropies during the Oct. 28-31, 2003 Halloween event

Authors: Kane, R P

Abstract: Using data from the Nagoya muon directional telescopes during the storm of 29 Oct. 2003, the anisotropies were traced at successive UT times. Some features were very prominent, positive in some directions, negative in others. In each, different directional telescopes indicated different magnitudes, implying large directional anisotropies. By tracing the anisotropies in space, one could conclude that the Earth was engulfed by the interplanetary blob and passed slightly in its northern part (same as North of Sun). These results are approximate, as the simple analysis was carried out assuming straight line paths for cosmic rays, while some bending in magnetic fields and some scattering may be involved. Nevertheless, useful information can be obtained even from one muon set up as shown here. Using more copious data from other sources would, of course, give more detailed information.

Page(s): 28-33