Observations On Solar Flares

Various aspects of solar flares such as dynamic phenomena, the relation to magnetic fields, electromagnetic radiations, particle emissions, and flare loops are discussed with attempts at classification in terms of observable effects. Discrepancies in defining the mechanisms that must exist stress the need for further observations. (Author).

This book provides results of analysis of typical solar events, statistical analysis, the diagnostics of energetic electrons and magnetic field, as well as the global behavior of solar flaring loops such as their contraction and expansion. It pays particular attention to analyzing solar flare loops with microwave, hard X-ray, optical and EUV emissions, as well as the theories of their radiation, and electron acceleration/transport. The results concerning influence of the pitch-angle anisotropy of non-thermal electrons on their microwave and hard X-ray emissions, new spectral behaviors in X-ray and microwave bands, and results related to the contraction of flaring loops, are widely discussed in the literature of solar physics. The book is useful for graduate students and researchers in solar and space physics.

This is a summary of the ten years (1955-1964) of observations of solar flares reported by 61 observatories. The flare reports have been published predominantly in the IAU Bulletin and CRPL-F Series Part B. This report summarizes the types of information contained in the flare reports, and the frequency of some parts of these reports as functions of many parameters. The results reflect the need for closer cooperation and coordination of participating observatories in recording and reporting solar flare data.

The Campaign for Integrated Observations of Solar Flares (CINOF) was a period of extensive solar flare studies conducted 5-29 June 1972. Specific scientists were designated as CINOF coordinators to study selected events. This compilation contains seven reports: Five reports detailing solar phenomena associated with CINOF selected flares, one report detailing observations of a flare initiated shock wave propagating through the interplanetary medium, and one report on the solar particle and associated interplanetary measurements during this period.

This volume is a collection of research articles on the subject of solar flares and flares on other cool stars, which are currently extensively studied using new ground- and space-based instruments, together with highly sophisticated numerical simulations. The collection memorializes the work of a pioneer in the study of solar physics, Professor Zdenek Švestka (1925 Prague – 2013 Bunschoten), a leading expert in the field of solar flares and the co-founder and Editor-in-Chief of the journal Solar Physics. The book contains many contributions to the conference “Solar and Stellar Flares: Observations, simulations and synergies”, held in Prague during 23 – 27 June 2014, organised in honor and memory of Professor Švestka. Originally published as Topical Issue of Solar Physics, Vol. 290, Issue 12, 2015.

ATS-satellite observations of sudden increases in total electron content (SITECs) produced by extreme-ultraviolet (EUV) and X-ray bursts of solar flares are presented quantitatively and interpreted qualitatively. Large SITECs for the white-light flare of July 4, 1974, and for the large flares on July 5, September 10, and September 19, 1974, are illustrated. The time rate of change of total electron content dN (subscript)T/dt was directly compared with SFD (Sudden Frequency Deviations) measurements. The ATS-6 dN(subscript)T/dt measurements are essentially transionospheric SFD measurements. The main difference with respect to ground-based SFD measurements is that, in addition to the 100 to 200 km altitude range where ionospheric electron loss rates are high, the ATS-6 measurements also observe the low loss-rate F2 region. Because of this low ionization loss rate, dN(subscript)T/dt includes more of the slow radiation effects and proceeds to a negative decay phase much later than the ground-based SFDs.

Sudden Ionospheric Disturbances resulting from an interaction of the Solar Flare radiation with the constituents of the upper atmosphere constitute one of the three major aspects of ground level monitoring of solar flares -the other two being optical observations of flares, and the observations of solar bursts in radio wavelengths. SIDs, therefore, form a major part of flare monitoring programme in many observatories. Unlike the other two, however, the ionospheric effects of flares provide one major additional source of interest - the reaction of the ionospheric plasma to an impulsive ionization. The high atmosphere provides a low pressure laboratory without walls in which a host of reactions occur between electrons, ions and neutral particles. The resulting products and their distributions may bear no resemblance to those of the primary neutral constituents or their direct ionization products. The variations with the time of the day, with season and with solar activity that form the bulk of the ionospheric measurements are too slow to allow any insight into the nature of these ionospheric reactions whose lifetimes are often very short. The relaxation time of the ionospheric ionization is only a few minutes or fraction of a minute in the lower ionosphere and in the E-region and is about 30 min to an hour at 300 km. The flares provide a sudden short impulse comparable to these time scales.