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Ruby Payne-Scott’s career as a radio astronomer began in 1944 and extended to her retirement in July 1951. Her remarkable career, which led to many of the early discoveries in solar radio astronomy, can be roughly divided into four phases. The early phase began in March 1944 and extended to late 1945, a period of transition from wartime radar research to early solar noise research. In this period Payne-Scott, under the leadership of J. L. Pawsey, along with others, was laying the groundwork for the beginnings of solar radio astronomy. The following period from October 1945 to late 1947 marked the groundbreaking solar work at Dover Heights and the publication of their first important research papers on solar physics. Her contributions to Fourier radio astronomy imaging were crucial at this stage. In 1948, Payne-Scott had an interlude working on her own at the Hornsby field station; the detailed properties of Type III bursts were elucidated in this period. Starting in 1949, up to the end of her career at RPL in July 1951, she was mainly involved in the building and use of the high resolution swept-lobe interferometer at Potts Hill Reservoir in Sydney, a collaboration with Alec Little. There was a brief coda in August 1952 during the URSI International Assembly in Sydney. In this chapter we will study the work Ruby did as a proto-radio astronomer in 1944 and 1945.

Recent overwhelming evidences show that the sun strongly influences the Earth’s climate and environment. Moreover existence of life on this Earth mainly depends upon the sun’s energy. Hence, understanding of physics of the sun, especially the thermal, dynamic and magnetic field structures of its interior, is very important. Recently, from the ground and space based observations, it is discovered that sun oscillates near 5 min periodicity in millions of modes. This discovery heralded a new era in solar physics and a separate branch called helioseismology or seismology of the sun has started. Before the advent of helioseismology, sun’s thermal structure of the interior was understood from the evolutionary solution of stellar structure equations that mimicked the present age, mass and radius of the sun. Whereas solution of MHD equations yielded internal dynamics and magnetic field structure of the sun’s interior. In this presentation, I review the thermal, dynamic and magnetic field structures of the sun’s interior as inferred by the helioseismology.

Understanding the high energy Universe has been a long standing goal of astro-particle physics.

The nature of solar surface magnetism has been an open problem in solar physics. In this paper we address three frontline problems of spectropolarimetry of the Sun. We first review the theoretical formulation and numerical solutions of Zeeman absorption and then the Hanle scattering phenomena in ‘turbulent magnetic fields’. We show that the mean emergent Stokes profiles cannot be obtained by simply averaging the scattering and absorption opacities, respectively, over a given distribution of the random field (except when the micro-turbulence prevails). A new formulation of the transfer equation is necessary to study the astrophysically interesting meso-turbulence case. Such formulations of the stochastic polarized radiative transfer problems for absorbing and scattering media are developed only in recent years. We review them and show some results computed by our new formulations.Until recent years the solution of the polarized line radiative transfer equation in LTE (Zeeman absorption in strong fields), and its NLTE counterpart (Hanle scattering in weak fields), were treated as two disparate problems. The reason for this artificial division was more due to the theoretical and numerical difficulties encountered in the solution of the combined Hanle-Zeeman radiative transfer equation. A very general form of the transfer equation was formulated only a decade ago, for the case of complete frequency redistribution. A more difficult case of partial frequency redistribution is explored by us recently. We review these developments through a study of the Hanle-Zeeman effect in arbitrary strength magnetic fields.

The Kodaikanal Observatory traces its origins to the East India Company, which started an observatory in Madras “for promoting the knowledge of astronomy, geography, and navigation in India.” Observations began in 1787 at the initiative of William Petrie, an officer of the Company, with the use of two 3-in achromatic telescopes, two astronomical clocks with compound pendulums, and a transit instrument. By the early nineteenth century, the Madras Observatory had already established a reputation as a leading astronomical center devoted to work on the fundamental positions of stars, and a principal source of stellar positions for most of the southern hemisphere stars. John Goldingham (1796–1805, 1812–1830), T.G. Taylor (1830–1848),W.S. Jacob (1849–1858), and Norman R. Pogson (1861–1891) were successive Government Astronomers who led the activities in Madras. Scientific highlights of the work included a catalogue of 11,000 southern stars produced by theMadras Observatory in 1844 under Taylor’s direction using the new 5-ft transit instrument.

Several important problems in solar radio physics can be attacked using the high spatial resolution observations from a low frequency space array, as the problem of ionospheric refraction does not exist. Noise storms are believed to occur in closed magnetic loops due to trapped superthermal particles. Recent radioheliograph observations suggest such a magnetic field topology up to altitudes of about 40 MHz emission. The problem of relative locations and sources of the storm continuum and bursts can be effectively studied by imaging them with higher spatial resolution. Interplanetary type II bursts are observed from heights above ~ 10 R⊙ while coronal type II bursts are observed from heights less than ~ 3 R⊙. Observations filling this gap have important implications for the understanding of solar-terrestrial relations through shocks and mass ejections.

Helioseismology is enjoying a tremendous surge of activity, spurred by the combination of reliable data and effective interpretation methods. Since I cannot do justice to the entire field, I attempt in this review to describe two current topics that I find interesting. (1) Several workers have now made measurements relating to the variation of rotation with depth and latitude inside the Sun. Most of the observations agree fairly well on the depth dependence, but not so well on the latitude dependence. I explain how such measurements are made, and discuss the current state of this controversy. (2) The driving mechanism for solar p-modes remains a mystery. The best (in my view) explanation involves stochastic driving of the modes by turbulent convection. This theory (proposed by Goldreich and Keeley) has recently been extended by Goldreich and Kumar in a way that illuminates some issues and obscures others. I attempt to provide a simple introduction to these ideas.

We review the space instrumentation that is currently being developed for studies of the Sun. Currently the main solar physics mission is SOHO, which has support from Yohkoh, Coronas I and a variety of “particles and fields” spacecraft such as Polar, Wind, Geotail and Interball. The principal new facility will be the TRACE mission, which is scheduled for launch in 1997/1998. For the medium term future, missions such as the Solar Probe, Coronas-F and Foton, plus the successor to Yohkoh are likely to be realised, at least in part. Other missions are in a definition phase, such as HESSI, SIMURIS and a STEREO mission of some form. New particle instruments which can detect solar emissions, such as ACE, will be launched before the year 2000. The ESA Horizon 2000+ program has some medium missions, yet to be defined, which should be devoted to solar studies.

The relationship between solar r-modes (long-period oscillations dominated by the Coriolis force) and solar activity cycles is investigated statistically. FFT power spectra of the daily Zurich sunspot numbers (R) and of the Greenwich Photoheliographic projected whole sunspot area (A) are obtained for the high-activity years of solar cycles 14 through 21. Both R and A are found to exhibit periods of 22 + or - 1 d, 34 + or - 1.5 d, and 43 + or - 2 d, corresponding to r-modes with (l,m) angular harmonics (2,2), (3,1), and (2,1), respectively.

Solar quiescent active regions are known to exhibit radio emission from discrete structures. The knowledge of their dimensions and brightness temperatures is essential for understanding the physics of quiescent confined plasma regions. Solar eclipses of 10 August 1980 and 28 January 1990, observed with high sensitivity (0.01 s.f.u.) and high time resolution (30 ms) at 22 GHz, allowed the unprecedented opportunity to identify Fresnel diffraction effects during lunar occultations of active regions. The present results indicate the presence of quiescent discrete sources smaller than one arcsecond in one dimension that can be associated to the compact sources of suprathermal microwave emission. Assuming symmetrical sources, their brightness temperatures were larger than 2x107 K and 8x107 K, for the 1980 and 1990 observations, respectively. From energetic point of view the results give new information about confinement of plasmas in active regions.

Solar physics requires more and more multiwavelength observations, not only with high spatial and time resolution, but also with wide coverage in space and time. We review briefly instruments dedicated to the solar interior, visible layers and the corona. In addition to the accuracy of spectroscopy and polarization measurements, we emphasize the coverage of data sets in the k − ω diagram. New image restoration methods are reviewed, in the context of the best compromise between spatial resolution and isoplanetic field of view. Ambitious projects do exist, as well as new generation telescopes under construction. Progress in the establishment of data bases and easier data exchange between observatories using complementary facilities look very promising for the future.

Powerful radio radiation often originates from the Sun at decametric and kilometric wavelengths. Radiation from the quiet Sun is produced by the thermal mechanism of bremsstrahlung, and radio bursts of several kinds are produced by the non-thermal mechanisms of plasma radiation and, rarely, gyrosynchrotron radiation.

The connection between solar radiobursts of type II and shocks has been largely recognized since many years; however, the details of radiobursts generation are not been fully understood yet. A two-step mechanism is often invoked including (i) the formation of electrons streams by shock waves and (ii) the excitation of radio emission by these streams. In the present report, we will focuss mainly on step (i) through results of numerical simulations mainly based on full particle electrostatic and electromagnetic codes. Such codes are appropriate to follow the overall dynamics of the shock itself and to identify the different sources of acceleration and heating of particles in a self-consistent way.

The CELIAS instrument is designed to study the composition of the Solar Wind (SW) and of solar and interplanetary accelerated energetic particles on SOHO (Solar and Heliospheric Observatory). It consists of three different sensors with associated electronics, which are optimized each for a particular aspect of ion composition. These aspects are the elemental, isotopic, and ionic charge compostion of SW or energetic ions emanating from the Sun. A fourth sensor, the Solar EUV Monitor (SEM) was included into CELIAS for monitoring the absolute EUV flux from the Sun.

High time resolution (Δt = 10s) photometric scans of chromospheric Ca+ K are examined for evidence of propagating waves. The scans refer to a quiet area (1 x 7 arc seconds) near disk center. Diagnostics include line profile movies, time sequence spectrograms and power spectra. Both upward and downward (reflected?) disturbances having lifetimes, ~ 1–2 minutes are seen.

On the sun we can identify many of the motions derived from stellar spectral analysis. A summary is given of the observed solar velocity phenomena. Many of these (e.g. meridional flow, giant cells, solar differential rotation, supergranula tion) are of great interest in astrophysics especially for interior structure and chromospheric and coronal structuring but contribute virtually nothing to the velocities derived from a solar irradiance spectrum analysis. Others (granulation, very small scale motions and to a lesser extent, oscillations) do contribute substantially to the integrated sun velocity analysis. Some of the properties of these motion fields are described.

In parallel with the development and deployment of solar space instrumentation a substantial effort is being made at many ground based observatories world-wide, not only to make better use of the available hours of sunshine, but also to reach out to new frontiers of solar research. Examples of novel instrumentation will be described, and some of the observational results will be discussed in the light of current problems in solar physics.

Solar models are calculated with low central hydrogen abundance. The stability of these models is investigated. The eigenspectrum is computed and compared with the SCLERA observations of solar oscillation.

Oscillations of the solar interior (linear g-modes) may be strongly driven by the collective influence of all the modes upon the nuclear reactions in the core. This heretofore neglected effect could couple the modes, reduce the effective amplitudes near the center, and spatially concentrate most of the oscillation energy into just a portion of the radiative interior. If operating at sufficient strength, this can reverse the conventional conclusion, drawn from single mode calculations, that almost all solar g-modes are damped. Furthermore, it would put the theory into rough harmony with three otherwise troubling observations: (1) the “low” neutrino flux measured by Davis (1978), (2) the high correspondence found by Wolff (1976) between recurrence periods in solar activity and the rotational beat periods of g modes, and (3) the fluctuations in the sun's diameter which imply g-mode activity at high angular harmonics (Hill and Caudell 1979). A nonlinear expression is derived for the local rate of work done on an array of oscillation modes by the nuclear reactions. Three additional tests of the model are suggested.

We postulate that the rotation and evolution of solar surface structure can function as a source of noise in solar limb definition measurements. To test this hypothesis, we have produced a time series of 216 spectroheliograms taken at two minute spacings. These spectroheliograms were obtained in an Fe I line, formed at a depth similar to optical depth unity at the limb. We foreshortened this data in order to simulate the solar limb brightness profile and passed it through the finite Fourier transform definition (FFTD) algorithm used by Hill and his collaborators at SCLERA. In this work we were able to determine the amount of variation in solar limb position which is attributable to evolutionary changes in solar surface structure. We also artificially rotated one of these surface structure functions in order to determine the effects which surface structure rotation might have on limb position. In this paper, we conclude that rotation alone can produce power only at low frequencies (w ≲ 1 mHz). However, the evolution of solar surface structure exhibits a power spectrum which is similar to that observed with the SCLERA instrument at all of the frequencies. We also show that standing surface structure patterns can produce phase for a period of seven days such as the phase coherence found in the observations at SCLERA, although in the case of the latter, the periods are significantly longer.

Isaak's announcement (Claverie et al. 1980) of the discovery by his group of distinct, approximately evenly spaced peaks in the power spectra of whole-disk Doppler measurements immediately raised the issue of what they imply about the structure of the solar interior. Here we report our immediate reactions, and infer that the observations seem to imply a lower sound speed, appropriately averaged throughout the interior, and probably a lower mean temperature than standard solar models predict.

The properties of the- linear modes of oscillation of a nonrotating nonmagnetic star, with particular reference to the sun, are briefly described. The most likely mechanisms by which they might be excited are reviewed, and it is concluded that stochastic excitation by turbulence is probably the dominant mechanism that drives the solar five minute oscillations. Phase coherence of one of the components of the SCLERA diameter data is illustrated, and the new five minute oscillations in the Birmingham whole-disk Doppler data are discussed. Finally some of the problems raised by conflicting evidence concerning the structure of the sun are aired, but not resolved.

Global solar oscillations have been shown to be primarily observable through changes in the solar limb darkening function. The observational search for these changes is hampered by problems associated with changes in the earth's atmosphere. Attempts by several investigators to deal with these problems are reviewed and the results are reproduced from the most successful of these. The pros and cons of the various techniques used in these observations are brought into focus by an analysis of their individual ability to deal with the earth's atmosphere.

This work deals with the subject of global solar oscillations. These oscillations are observed as fluctuations in the diameter of the sun. A diameter is determined by a mathematical solar edge definition at the SCLERA1 instrument. The oscillations have periods ranging from a few minutes to several hours and have amplitudes measured in millionths of a solar radius. These small amplitudes are observable only due to the unique properties of the edge definition. The properties of the observed solar oscillations are determined from the data; their statistical significance and repeatability are then tested.

Solar g modes with l 1 to 4 and periods near 160 minutes have been investigated using a solar model with normal structure. Radiative dissipation in the region below the convection zone is much greater than the driving provided by nuclear reactions or the opacity mechanism. A crude treatment of convection suggests that it also is not an important source of driving. The damping due to turbulent viscosity is also small. Excitation of these modes by coupling to convective turbulence is substantial in terms of the rms energy of the modes, but the surface velocity is very small because of the large amount of mass involved in the oscillation.

The dependence of theoretical eigenfrequencies of five minute oscillation modes on the parameters that determine model solar envelopes has been investigated. It was found that the p mode frequencies are quite strongly correlated with the depth of the convection zone. Comparison of theory with observation suggests that the solar convection zone is about 200,000 km deep.

SOHO, the Solar and Heliospheric Observatory, is a joint ESA/NASA mission to study the sun from its interior to, and including, the solar wind in interplanetary space. It is currently scheduled for launch in 1995. In this paper a mission overview is given, comprising scientific objectives, payload, spacecraft, operations, and data and ground system.

The interpretation by Hill and Caudell (1979) of some of their solar oscillation data as being due to g modes of degree greater than 20 seems to imply that the solar convection zone is much shallower than that in standard solar models, probably representing only a few per cent of the radius. We attempt here to match the observed periods in models of this nature; the rather complicated spectrum of oscillations in such models can be understood in terms of the asymptotic behavior of modes of large degree. Possible excitation mechanisms for the modes are briefly discussed.

An automated neural network-based system for predicting solar flares from their associated sunspots and simulated solar cycle is introduced. A sunspot is the cooler region of the Sun’s photosphere which, thus, appears dark on the Sun’s disc, and a solar flare is sudden, short lived, burst of energy on the Sun’s surface, lasting from minutes to hours. The system explores the publicly available solar catalogues from the National Geophysical Data Center to associate sunspots and flares. Size, shape and spot density of relevant sunspots are used as input values, in addition to the values found by the solar activity model introduced by Hathaway. Two outputs are provided: The first is a flare/ no flare prediction, while the second is type of the solar flare prediction (X or M type flare). Our system provides 91.7% correct prediction for the possible occurrences and, 88.3% correct prediction for the type of the solar flares.

Magnetic reconnection is an important mechanism in astrophysics for converting magnetic energy to both thermal energy and bulk acceleration of plasma and also for changing the global topology of the magnetic field. For over 50 years now solar theorists have investigated reconnection. This paper provides a basic review of the classical aspects of reconnection in both one, two and three dimensions, as well as, giving a potted history of reconnection theory in solar physics. Magnetic annihilation, Sweet-Parker reconnection and Petschek reconnection will all be discussed as will spine and fan reconnection in three dimensions.

This book grew out of research on the size of the Sun and may be summarized in a single sentence: “How big is the Sun?”. This question, at a first glance quite trivial, is not so devoid of interest. Indeed, by opening any good monograph on the Sun, one may find basic data, namely for our purpose here, solar radius and solar radiation. It is known that these two key parameters are closely linked, so why to go further? Let’s go just a bit deeper: do we really know the absolute value of the Sun’s diameter? Do we know if there is a temporal variability of this diameter? Do we know exactly the oblateness of the Sun? What are the values of the solar gravitational moments (which points out the outer shape of the Sun as well as the internal distribution of masses and velocities)? Are we able to model the fluctuations of the solar irradiance on short time scales? Is the luminosity altered by sub-surface phenomena? And in addition to the solar physics aspects, are we today able to investigate correctly the terrestrial implications? And so on.

Basic concepts in solar physics are described with an attempt to bring out the importance of the Sun as a “Rosetta Stone” to understand other stars. Our Sun being the nearest star, shows intricate surface details and a wide variety of dynamic phenomena. These range in size from a few kilometres to millions of kilometres and in the temporal domain from a fraction of a second to decades. In addition, the Sun displays a great variety of magnetic and velocity fields, as well as radiative energy spectra. The close connection between the solar activity and the Earth’s ionosphere, atmosphere and geomagnetic field makes the Solar-Terrestrial relations a very interesting and valuable field of study for a whole variety of disciplines. The principles and details of various kinds of solar instruments are described, especially solar telescopes from the simplest to the advanced types, along with several kinds of back-end instruments, such as monochromatic filters, spectrographs, spectroheliographs, magnetographs, etc., used for photospheric, chromospheric and coronal observations. Standard techniques for making solar observations, e.g., measurements of sunspot areas, coordinates and position of solar features, etc., are described. Solar observations made even with simple equipments are of great importance for short and long term synoptic studies and can even be taken up as a hobby by amateur solar astronomers along with professional solar physicists.

Overview of Solar Physics.- Instrumentation and Observational Techniques in Solar Astronomy.- Solar Interior and Seismology.- The Active and Explosive Sun.- Magnetic Flux Tubes and Activity on the Sun.- Solar Magnetic Fields.- The Physics of Chromospheres and Coronae.- The Solar Corona.- The Solar Wind.

Plasmas in interplanetary space originate from the Sun, as do most of the disturbances and waves embedded in them. The solar atmosphere, the corona, extends as solar wind far beyond the orbit of the outermost planet, Pluto, filling a cavity in the interstellar medium called the heliosphere. The solar magnetic field, frozen-in into the solar wind, is carried out and wound up to Archimedian spirals by the Sun’s rotation. Fluctuations and waves on different scales are superimposed, sometimes steepening to collisionless shock waves. The solar wind and the frozen-in magnetic field change during the solar cycle due to systematic changes in solar properties and transient disturbances related to solar activity. Detailed accounts on solar physics and the physics of the interplanetary medium are given in e.g. [113, 484, 572], and the solar corona and the physics of solar activity are described in e.g. [9,193, 244, 291, 410, 420, 424].

Solar observations now require many capabilities: high resolution to detect fine flux tubes, polarization-free optics to measure the vector magnetic field, spectral range including many lines to disentangle thermodynamic from magnetic signatures. The site of Canary Islands, the active optics, the Cassegrain telescope, the long spectrographs and the universal filter of THEMIS fulfill many conditions for major advances in the near future of solar physics.

Schwarzschild’s scientific contributions to the fields of solar physics and of the physics of stellar atmospheres were concentrated in two periods. The first began with his observation of the total solar eclipse of 1905 August 30 in Algeria, and covered the years 1905–1906. After several years break, he again became active in this field in 1913–1914.

It has been suggested by Parker (1983, 1988), Sturrock et al. (1990), and others that the corona may be stochastically heated, on spatial scales at or below current instrumental resolution limits, by a continuous succession of many small flarelike events commonly referred to as nanoflares. In this paper we extend a semi-analytical “point” model developed previously for solar compact flares (Kopp and Poletto, 1990), to include gravitational plasma downfall during the late decay phase. Applying the model to conditions representative of nanoflares allows us to predict the temporal variation of average plasma properties in such events and should ultimately facilitate a calculation of the spectral characteristics of a nanoflare-heated corona.

A series of numerical simulations indicates that quasi-impulsive thermal energy releases of ~ 1026 ergs in a narrow region of the upper chromosphere of a quiet region coronal loop can provide a transient heating source for the corona. Lower energy events radiate away their energy too quickly to generate substantial temperature enhancements. The microflares seen in UV images may generate such energy releases, and may also be the source for some of the dynamic events seen in UV spectra.

Long-period acoustic waves generated in the solar convection zone can propagate radially outward through the overlying atmosphere and get resonantly absorbed in the magnetic arches of the low-lying chromospheric canopy. The resulting Poynting and acoustic flux that enters the magnetic canopy in the network regions is demonstrated to be adequate to account for the observed chromospheric emission.

The SIMURIS Mission, dedicated to ultrahigh resolution imaging and spectroscopy of the solar atmosphere from the convection zone to the high corona, has two major instruments: the Solar Ultraviolet Network (SUN) which is a 4 telescopes interferometer capable of 10 km spatial resolution on the Sun, and the Imaging Fourier Transform Spectrometer (IFTS) which provides multispectral instantaneous 2D velocity fields of the solar atmosphere. SIMURIS was proposed to ESA in November 1989, and accepted for an Assessment Study in the context of the Space Station in February 1990. The main scientific objectives are outlined and the model payload is briefly described. In particular, the interest of high angular resolution to understand the coronal loop structure is illustrated on selected examples since current observations are unable to distinguish in between different dissipation/heating theories such as current built up and resistive instabilities, current built up in singular layers and reconnection, or resonant MHD wave excitation and dissipation.

An analysis of long data stretches covering the years 1982–1987, obtained from a whole disc optical resonant scattering spectrometer, indicate the presence of significant signals in the 25–75 µHz frequency range. The period spacings of these signals are found to be in four groups, which, determined independently for each year, are not only consistent but correspond with the predictions of the Tassoul (1980) asymptotic theory. Further, an investigation of the phase coherence of specific signal frequencies indicate life-times of several hundred days. These signals therefore show all the anticipated characteristics of solar g modes.

Whereas previous spectroscopic studies of impurity crystalline substances have revealed the possibility of their utilization in lasers, the experience accumulated in studying the parameters of their laser emission has in turn given rise to a new spectroscopic trend, stimulated-emission spectroscopy of activated crystals. In conjunction with such conventional techniques as luminescent and absorption analyses, this new spectroscopic method is at present being widely used in studying the nature of phenomena that occur in excited active media ; it is also of great help in solving such a challenging problem as the search for new, more-efficient laser compounds. All the evidence presented in this book indicates convincingly that stimulated-emission spectroscopy provides a substantial contribution to the recognition of new stimulated-emission potentialities of already known laser crystals. The proportions of this contribution, as given in various stages of the development of the physics of laser crystals over nearly twenty years, are illustrated in Fig. 9.1.

Solar Oscillations, with frequencies between 2 and 5 mHz, can be identified as p modes with well-determined degree 1 and overtone number n, but minor discrepancies, of order 10 MHZ, between observed and calculated frequencies remain. We describe the computation of solar models and their frequencies of oscillation, check the accuracy of the numerical results, and study the influence of the atmosphere. Attempts to improve the calculated frequencies for low degree and intermediate order (n=10…20) have so far been unsuccessful.