AJP	ISSN : 0971 – 3093 Vol  16, No. 2 & 3, April-September, 2007

Asian
Journal of Physics

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Special issue on Space Weather
Guest Editors
P Janardhan, Hari Om Vats
K N Iyer, B G Anandarao
Special Issue on Space Weather, Vol 16, Nos 2&3, 2007

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Preamble

The magnetic field in the space around the Sun called heliosphere evolves in response to the magnetic field at the base of the photosphere of the Sun. This evolution, together with the rotation of the Sun, drives space weather through the continually changing conditions of the solar wind and the magnetic field  embedded within it. Given this broad framework, it is apparent that the near-earth environment, viz. the earth’s magnetosphere and ionosphere are continually affected by the Sun. Hence conditions in the near-earth environment are linked to the underlying disturbances in the solar magnetic field and can manifest themselves in different ways depending on the local conditions on the Sun. The phenomenal growth in the space-based technological systems, in the recent times, coupled with the growing needs of modern civilization makes it imperative for mankind to be able to predict “weather” or in other words, the conditions prevailing in the near-earth environment and the inner heliosphere i.e. the space between the Sun and the Earth. Thus, this entire space environment  is governed indirectly and/or directly by processes taking place in the Sun itself.

The Sun affects space not only by its radiation but also by spewing out particulate matter (or plasma) containing energetic electrons and protons. A vast variety of energetic solar phenomena like solar flares, filament eruptions, coronal mass ejections and other solar wind phenomena constantly change the space environment generating a variety of plasma instabilities under the influence of solar and interplanetary magnetic and electric fields. As a result of these violent activities going on in the Sun, the interplanetary medium is not homogeneous but interspersed with density irregularities that affect the radio wave propagation by producing scintillations akin to the twinkling of stars in the visible radiation. Solar wind interaction with the Earth’s magnetosphere can cause changes in the earth’s ionosphere that can adversely affect radio communications. Energetic solar particles are also immensely hazardous to the well-being of the artificial satellites that are ever increasing in numbers. The Earth’s ionosphere too displays a variety of plasma instabilities that cause irregularities in its density structure.

Space weather studies are basically meant to unfold this coupled and highly complex Sun-Earth system or Sun-Planet system. The importance of understanding space weather is so overwhelming that a large number of solar and ionospheric scientists are coming together all over the world in a connected effort to address the ultimate goal of predicting solar and space weather phenomena. Coordinated multi-wavelength observations and theoretical modeling are going on hand-in-hand to understand how to cope up with “living with a star” i.e. the Sun and the interest in this field is growing by leaps and bounds.

This special volume is a humble attempt to address and review a few  issues on space weather. It contains articles on basic physical processes in the Sun which lead to energetic and often explosive activity as well as the effects of these on the interplanetary medium and the ionosphere of the Earth. The authors of the articles are all eminent scientists actively working in the field. The articles attempt to bring out how near or how far we are in our understanding of the Sun, the solar wind and space weather. All the articles have been given editorial attention so far as general readability is concerned; the technical issues are left mostly to the authors valuable judgement. We express our sincere gratitude to all the authors for their cooperation and enthusiasm in contributing to this special volume. We thank Ms Karanjgaokar for help with the manuscripts and figures.

 

P Janardhan, Hari Om Vats, K N Iyer and B G Anandarao

Guest Editors

 

Asian Journal of Physics

Vol 16, Nos 2&3 (2007) 97-307

 

CONTENTS

Guest Editorial

Space weather simulations in 3D MHD from the Sun to Earth and beyond to 100 AU: A modeler’s perspective of the present State of  the Art
Murray Dryer

 97

 

The magnetic origin of coronal mass ejections

A Nindos

123
 

Magnetic field of the coronal mass ejection source regions                                                           

Debi Prasad Choudhary

147

 

Solar flare reconnection, plasmoid ejection, loop-top X-ray sources and associated radio bursts

M Karlický

165

 

Solar radio bursts and space weather

Stephen M White

189

 

Insights from ground and space based observations of long lasting low density anomalies at 1 AU 

P Janardhan, S Ananthakrishnan, and V Balasubramanian

209

 

Electron acceleration in solar noise storms                                                                    

Prasad Subramanian

233

 

Impact of space weather events on the coupling of ionosphere and thermosphere over low latitudes 
R Sekar and D Chakrabarti

247

 

Effects of recent space weather events in the equatorial and low latitude F-region in the Brazilian sector: A review

Y Sahai, F Becker-Guedes, P R Fagundes, F L Guarnieri, A J de Abreu, R de Jesus, V G Pillat, W L C Lima and J A Bittencourt

273

 

Rotation of the Sun and its atmosphere

Hari Om Vats

 

 

Vol 16, Nos 2&3(007) 97-122

Space weather simulations in 3D MHD From the Sun to Earth and beyond to 100 AU: A modeler’s perspective of the present State of the Art

 

Murray Dryer

NOAA Space Environment Center

National Weather Service, Boulder, Colorado 80305,USA

Exploration Physics International, Inc

Significant strides have been made to simulate and to forecast the state of the solar wind at Earth and beyond under both “quiet” and “solar event-driven” conditions. A key physical condition, the solar wind speed, has been successfully predicted thus far under real time operational conditions. This property includes equal proton and electron speeds by assuming charge neutrality.Still beyond our reach, however, are conditions such as the IMF (interplanetary magnetic field, B) components, especially By and Bz,despite the efforts of various three-dimensional, magnetohydro-dynamic (3DMHD) modeling efforts.

This need for continous benchmarking includes the IMF topological paths for shock-energized, gradual enhancements of solar energetic particles (SEPs) fluxes from impending shock waves. Local enhancements of energetic storm particles (ESPs) upon shock arrival at an observing spacecraft at Mars are also briefly discussed. These objectives are essential for geospace predictions for societal reasons described elsewhere.

Total Refs : 73

 

M Dryer – Asian J. Phys, 2007

 

Vol 16, Nos 2&3(007)123-146

The magnetic origin of coronal mass ejections

 

A Nindos

Section of Astrophysics, Physics Department, University of Ioannina, Ioannina  GR-45110, Greece

Coronal  mass  ejections (CMEs) are large-scale expulsion of coronal plasma and magnetic field. In this  article, I review the physics of CME initiation which resides in the magnetic field. Magnetic free energy and magnetic helicity are accumulated into the corona, and the magnetic structure is gradually driven away from possible minimum energy states. At some point the system becomes so stressed that the force balance breaks down by the development of either an ideal instability/loss of equilibrium or reconnection. Subsequent failure of magnetic field confinement gives rise to a CME. Diverse approaches about the details of the processes leading up to CMEs have been developed and presented here. © Anita Publications. All rights reserved.

 Vol 16,Nos 2&3(2007)165-188

 Solar flare reconnection, plasmoid ejection, loop-top X-ray sources and

associated radio bursts

 

M Karlický

Astronomical Institute, Academy of Sciences of Czech Republic

The 2-D Magneto-Hydrodynamic (MHD) model of the flare magnetic field reconnection shows that a reconnection activity, changes of the magnetic topology and generation of waves are closely related. It is found that after the phase of a quasi-stationary reconnection in the extended current sheet above the flare arcade, the tearing mode instability produces moving (ejected) plasmoids which can interact and generate additional MHD waves.Then a mechanism of acceleration of electrons in the collapsing trap formed in the flare arcade below the current sheet is studied using the MHD and test particle models. Computing the X-ray emission of the accelerated electrons, it is shown that the acceleration process in the collapsing trap easily explains the formation of observed loop-top X-ray sources. Furthermore, the acceleration of electrons during the tearing and coalescence processes in the current sheet is studied by the 2.5-D particle-in-cell simulation. Finally, all these processes are discussed from the point of view of possible radio emissions. While shocks can contribute to the type II radio bursts, the super- thermal trapped in plasmoids can generate the so called drifting pulsating structures. Furthermore, regions with the MHD turbulence, e.g. plasma reconnection outflows, may manifest themselves as the lace or dm-spike bursts. The radio emission transmitted or reflected from periodic density structures, e. g. in ion-sound shocks, can generate the zebra-like bursts.

© Anita Publications. All rights reserved.

Total Refs: 42

1. Priest E R, Forbes T, Magnetic Reconnection: MHD Theory and Applications, (Cambridge University, Press, Cambridge, UK), 2000.

2.Tsuneta S, Hara H, Shimizu T, Acton L W, Hudson H S, Ogawara Y, Pub Astron Soc, Japan, 44(1992)L 63.

40. Sagdeev R Z, in M A Leontovich (ed) Reviews of Plasma Physics 4, Publ. Consultant Bureau, New York, (1966)23.

41. Barta M,  Karlický, Astron Astrophys, 450(2006)359.

Vol 16, Nos 2&3 (2007) 189-207

Solar radio bursts and space weather

 

Stephen M White

Department of Astronomy, University of Maryland, College Park, M D20742, USA

Space Weather is the study of the conditions in the solar wind that can affect life on the surface of the Earth, particularly the increasingly technologically sophisticated  devices that are part of modern life. Solar radio observations are relevant  to such phenomena because they generally originate as events in the solar atmosphere, including flares, coronal mass ejections and shocks, that produce electromagnetic and particle radiations that impact the Earth. Low–frequency solar radio emission arises in the solar atmosphere at the levels where these events occur: we can use frequency as a direct measure of density, and an indirect measure of height, in the atmosphere. The main radio burst types are described and illustrated using data from the Green Bank Solar Radio Burst Spectrometer, and their potential use as diagnostics of Space Weather is discussed. © Anita Publications. All rights reserved.

Total Refs: 39

Cited by 61

Vol 16, Nos 2&3 (2007) 233-246

Electron acceleration in solar noise storms

 

Prasad Subramanian

We present an up-to-date review of the physics of electron acceleration in solar noise storms. We describe the observed characteristics of noise storm emission, emphasizing recent advances in imaging observations. We briefly describe the general methodology of treating particle acceleration problems and apply it to the specific problem of electron acceleration in noise storms. We dwell on the issue of the efficiency of the overall noise storm emission process and outline open problems in this area. © Anita Publications. All rights reserved.

 Vol 16, Nos 2&3(2007)247-272

Impact of space weather events on the coupling of ionosphere and thermosphere over low latitudes

 

The effects of space weather events on the ionosphere-thermosphere system(ITS) over low latitudes have been studied over the decades and there exists considerable amount of work in the literature.However, the present communication reviews the results obtained in Physical Research Laboratory in last few years based on coordinated optical,radar and other ground-based measurements supplemented by satellite-borne measurements by others. Recently obtained evidences for the effects of interplanetary electric field (IEF), on OI 630.0 nm nightglow and on the development of Equatorial Spread-F (ESF), are discussed here. The influences of space weather events on OI 630.0 nm dayglow emission and on the temperature of thermosphere are indicated. The gravity wave modes associated with space weather events are also addressed. © Anita Publications. All rights reserved.

Vol 16, Nos 2&3(2007)273-290

Effects of recent space weather events in the equatorial and low latitude F-region in the Brazilian sector: A review

 

Vol 16, Nos 2&3(2007)273-290

Rotation of the Sun and its atmosphere

 

Hari Om Vats

Physical Research Laboratory, Ahmedabad-380 009, India

The rotation of the Sun and its atmosphere is extremely complex. In the recent years a great deal of research work has been carried out on this subject to learn and understand the physics and the consequences of this in the realm of space weather. This article is an attempt to review the important findings and their implications. The main emphasis is on the recent  results in this field. The salient rotational features of the solar interior, photosphere, chromosphere and corona will be discussed. These    estimates are based on solar observations by satellite and ground based instruments operating at various frequencies in the entire electromagnetic spectrum of the Sun. © Anita Publications. All rights reserved.

Total Refs: 53