ASIAN JOURNAL OF PHYSICS

An International Peer Reviewed Research Journal
Frequency : Monthly,
ISSN : 0971 – 3093
Editor-In-Chief (Hon.) :
Dr. V.K. Rastogi
e-mail:[email protected]
[email protected]

Vol. 17, No.3 &4 (2008) 319-345

In this review we discuss the concept of the solar flare and associated phenomena. We began with very small-scale solar flare activity such as umbral dots occurring inside the sunspot’s umbra. We present recent evidences for the umbral dots to be the result of magnetoconvection in the photosphere. We also discuss recent discoveries in contrast to previous studies of light-bridges, and their context to flare associated phenomena. The opposite polarity of the light-bridge with respect to its parent sunspot was demonstrated and thereby how low-altitude reconnection causes mass ejection associated with flare/ Ellerman bombs is proposed. We define elaborately the concept of the flare in general and “confined” and “eruptive” classes of flares in particular. The various flare associated phenomena such as surges, spray and veil emission, flare loops have been reviewed with current status on these topics. These subjects have been changing with revolution in observational capabilities. In last two decades YOHKOH, SOHO, TRACE, RHESSI and SOXS, and more recently Hinode missions have changed the earlier concepts significantly, which have, however, enabled us to improve our understanding of this phenomenon on one side, as well as to improve our theories on the other side. The particle acceleration has been reviewed considering as a focal theme subject. The subject of microflares and nanoflares has been always a center of attraction among solar physicists since Parker [1] proposed them as potential candidates for coronal heating, which, however, does not convincingly appear the case, and we made full efforts to describe this phenomena in greater detail. We end this overview with a detailed discussion on how flare/ CME models and theories have changed over time. In this limited review we may not be able to cite the literature comprehensively, but we do try to give both early and modern references wherever possible.

Total Refs : 158

Vol. 17, No.3 &4 (2008) 347-362

Solar flare associated magnetic changes in solar active regions is a long-lasting issue in solar physics. The relevant observational studies have been done in three inter-connected directions: (1) the pre-flare magnetic configuration and evolution, (2) the rapid magnetic changes in the course of flares, and (3) the flare-induced signals in polarization measurements. The importance of these studies is to examine our physical understanding on the flare phenomenon which takes place in a wide range of astrophysical subjects. Although it is well established that flares come from the magnetic energy release in strong magnetic fields of the Sun and stars, current theoretical models are still far from being confronting the detailed observations. In this article we have tried to review some key advances in the relevant studies and suggest possible directions for the future.

Toatal Refs : 83

 Vol. 17, Nos. 3 & 4  (2008) 363-382

Solar flares and associated phenomena

A solar flare was first observed in 1859, and since that time scientists have been driven to understand and ultimately predict the most energetic phenomena in the solar system. Flares usually occur in regions with strong magnetic fields located in sunspots, and generally speaking this follows an activity cycle of approximately 11 years. Flares are often related to coronal mass ejections and have an impact on the space weather that surrounds the planets. In this review I will describe the latest understanding on solar flares derived through new simulations and from observations from a wide range of space missions including TRACE, SOHO, RHESSI and the recently launched Hinode and STEREO missions.

Total Refs : 100

 Vol. 17, Nos. 3 & 4 (2008) 383-410

High-temperature emission from solar flares

Some of  the most significant advances made with spacecraft instruments observing high-temperature emission from solar flares are reviewed. Solar flares have a basic geometry consisting of a loop or loop system. Model loops include conduction and radiation cooling mechanisms, and correctly predict some of the features, though the nature of bright loop-top sources is not explained: they may be associated with hard X-ray, nonthermal sources above the loop or loop system. Dielectronic satellites of Li-like Fe ions remain the best means of determining the temperature (~ 20 MK) of the hottest part of flares. A superhot component (up to ~ 40 MK) is indicated by the presence of H-like Fe ion line emission. Densities have been determined from line ratio techniques to be as high as 1019 m–3 at flare peak, but more generally 1018 m–3, and 1017 m–3 during flare decay. Mass motions are observed at the flare onset; there is more evidence that upflows result from chromospheric evaporation at flare footpoints. Nonthermal electrons have been detected spectroscopically. Line ratios may eventually give a useful means of determining the lower limit of nonthermal electron distributions at the flare impulsive stage. Finally, the importance of the spectral region 0.12 – 0.16 nm (7.5 – 10 keV) is emphasized. Fe XXV lines with 1s2-1snp (n > 2) transitions  with Fe XXIV satellites offer the means of determining the temperature of the hottest part of the flare and for detecting nonthermal excitation. Micro-calorimeter observation of this region could reveal much physics for large flares and for non-solar sources.

Total Refs : 51

Vol. 17, Nos. 3 & 4 (2008) 411-421

Looptop impulsive hard X-ray source in solar flares observed with Yohkoh/HXT

A new type of coronal hard X-ray source was first reported in 1994. That hard X-ray source was located above the soft X-ray loop and shows an impulsive behavior similar to those of the footpoint sources. Many solar physicists have tried to understand this source.  However, still there remain many problems.  In this paper, the researches related to this source observed with Yohkoh/HXT are reviewed.

Total Refs: 25

 Vol. 17, Nos. 3 & 4 (2008) 423-444

In this review article we firstly describe the X-ray emission from the solar flares and the focal science aspects that require the X-ray spectroscopy to improve understanding of the solar flares. We present briefly the X-ray spectroscopy carried out with scintillation detectors mounted onboard SMM and YOHKOH in last century, and then with next generation solid state detectors onboard  RHESSI and SOXS missions in this decade. We consider the X-ray high resolution spectroscopy as important diagnostic tool to understand the solar flares mechanism, and therefore we present in particular the instrumentation details, and results from Si and CZT detectors of SOXS mission in this article, which may enable youngsters to plan next generation space-borne experiments with superb resolution using advance technology.

Total Refs : 52

The detection of helioseismic signature of flares has opened up new possibilities for comprehending the seismic activity of the Sun and flare dynamics. In this review, I focus on the current state of our knowledge relating solar flares to oscillations of the Sun. 

Total Refs : 70