The impact of varves on solar physics

The discovery of 680-million year old varves by George Williams in South Australia, recording several millennia of fossil solar cycles, is a most exciting development that is bound to make an impact on solar physics. Already new problems of physical understanding have been posed by the 315-year Elatina cycle and the separate 350-year cycle, or undulation (Williams, 1985, 1986; Williams and Sonett, 1985). The Elatina cycle evidences itself multiplicatively in the form of amplitude modulation with a distinctive nonsinusoidal envelope, while the undulation is additive and quasisinusoidal (Bracewell and Williams, 1986). Both of these periodic phenomena are present in historical records of sunspots, but would not have been discerned from modern solar observations, which do not date back far enough. The explanation of two such sharply defined periods, in addition to the less sharply defined 22-year magnetic cycle, will require an understanding of solar physics that we do not yet have. Examples of the impact that the varve discovery is beginning to make are given, and a previously proposed mechanism for driving the activity cycle is extended in terms of a magnetic wave propagated radially outward from a deep torsional oscillator.Invited Talk to the 2nd Solar Cycle Workshop.     

A space-borne solar stereoscope experiment in solar physics

A space experiment project is proposed, with the main purpose of obtaining 3-dimensional images of the solar atmosphere. We give a list of problems and objectives which can be resolved through the space-borne solar stereoscope.     

The future of solar physics

The future of solar physics is founded on the existing fundamental unsolved problems in stellar physics. Thus, for instance, the physics of stellar interiors has been called into serious question by the very low-measured neutrino flux. The ⁷¹Ga neutrino detection experiment is the next step in unravelling this mystery. If that experiment should find the expected neutrino flux from the basic p-p reaction in the Sun, then astrophysics is in a difficult situation, because the most likely explanation for the low neutrino flux found in the ³⁷Cl experiment would be an error in our calculation of the opacity or an error in our understanding of the elemental abundances in stellar interiors, with serious implications for present ideas on stellar structure and the age of the galaxy.The new methods of helioseismology, for probing the interior of the Sun, have already found the primordial rapid rotation of the central core. The forthcoming world-wide helioseismology observing network will permit fuller exploitation of the method, promising to provide the first direct sounding of the interior of a star, hitherto known to us only through theoretical inference and the discrepant neutrino emission.The activity of all stars involves much the same phenomena as make up the activity of the Sun. The effects are too complex, and too foreign to the familiar dynamics in the terrestrial laboratory, to be deciphered by theoretical effort alone. It has become clear through the observational and theoretical work of the past decade or two that much of the essential dynamics of the activity of the atmosphere takes place on scales of the order of 10² km. Thus, an essential step in developing the physics of stellar activity will be the Solar Optical Telescope (presently planned by NASA to be launched early in the next decade) to permit a microscopic examination of the surface of the Sun to study the source of the action. The activity and X-ray emission of other stars depend on much the same effects, so that the study is essential to determining the significance of the X-ray emission from other stars.This work was supported in part by the National Aeronautics and Space Administration under grant NGL-14-001-001.     

Structure and physics of solar faculae

The OSO-8 satellite enabled us to study various characteristics of the profiles of Si ii, Si iv, C iv, and O vi lines above active areas of the Sun, as well as above quiet areas, and to derive some physical properties of the transition region between chromosphere and corona (CCT): (i) The study of the lines shows a general tendency for the microvelocity fields on the average to be nearly constant for the heights corresponding to T > 10⁵ K; however they seem to slightly increase with height in quiet areas, and decrease in active areas. (ii) A multicomponent model of the CCT is however quite necessary, and its geometry is far from being a set of plane-parallel columns. It is similar to an association of moving knots within the non-moving principal component of the matter. (iii) The proportion of mass, in the knots relative to that in the non-moving component, is several times larger in active regions than in quiet regions. (iv) In the knots, the non-thermal microvelocity fields are smaller in active regions and seem to decrease for T increasing above 10⁵ K, contrary to what happens in the steady principal component. Of course, we consider that microturbulence and Doppler shift are two aspects of the same distribution of velocity.     

Structure and physics of solar faculae

The methods used and the results obtained in the measurement of the distances between the centers of chromospheric granules are described. A coincidence of these structures at two different altitudes was observed. Observations made in the K2v, or in the K3 and CN lines permit the comparison of two different altitudes: the upper and the lower chromosphere. These results include flocculi on the edge of the supergranules as well as plages. Two main results are obtained: (l)the most likely distance between two neighboring granules is, at the minimum of the solar cycle, of about 2. 60 for K3 and 2.45 for CN, and (2) this distance is decreasing with growing solar activity.     

Planar solitonic filaments in solar physics

A new class of analytical solution of the coupled system of Da Rios-diffusion equation in magnetohydrodynamic (MHD) representing solitonic vortex filaments is obtained. One of the solutions is similar to the one found by Rogers and Schief describing a solitary wave propagating along a constant torsion vortex filament. Scalar magnetic diffusion equations are obtained by decomposing the magnetic filament along Frenet frame. The integral invariant of curvature is used to place limits on the diffused 100 eV plasma filament curvature. The resistivity of η=5×10^?5 ohm?cm—close to the stainless steel limit is used to approximate the Frenet curvature. From the scalar diffusion equations the vortex filaments are constrained to move along torsionless (planar) trajectories. Da Rios equations are coupled to diffusion equation to obtain a solitonic vortex diffused filaments. Due to bounds in time and length L we show that the model discussed is particularly useful in solar physics.     

Structure and physics of solar faculae

Si iv, C iv, and O vi resonance lines have been measured above quiet and active solar regions from both pointed OSO-8 instruments. From calibrated profiles, optical depths are computed with three different methods. All three methods provide evidence that the opacity above faculae is lower than above the quiet Sun. From lower and upper limits of the opacity, we derive limits of the electron density. Our first method assumes only that the source function is constant without any geometrical constraint. We find higher densities above faculae than above quiet regions (about a factor 10). A second method allows us to compute the density, temperature gradient and thickness of a plane-parallel model, for active and quiet Sun. Electron densities agree with those of the first method but they lie in the lower range of values previously determined from Skylab. This result can be explained by the moderate level activity of the observed faculae. Appendices give relevant elements of transfer theory and newly computed values of collisional rates.     

Structure and physics of solar faculae

Taking into account the effect of roughness (or local departures from sphericity) of the emitting layers in the chromosphere-corona transition zone (CCT) allows one to determine the optical depths of layers responsible for resolved structures in Cii, Ciii, Oiv, and Ovi lines. The result, at the top of the irregularities, is of the order of respectively ₁ 3.5,2.0, 1.6,0.5, and for the bottom of these irregularities, ₂ = 0.7, 0.4, 0.3, 0.25. The characteristic angle of these irregularities is, respectively, of the order of 35 °, 33 °, 35 °, and 41 °. For unresolved structures of Civ and Ovi (already analyzed in the spherical symmetry hypothesis in Paper III), one finds ₁ 0.6; 0.9 and ₂ 0.12; 0.2 in the case of quiet areas; in the case of active areas, the range is broader for Civ and Ovi, from 1.0 to 1.7 for ₁ and from 0.2 to 0.9 for ₂. The values obtained from Ovi are in reasonable agreement with each other for resolved and unresolved structures. And the obtained values of ₁ and ₂ correspond not too badly with the determinations made in Paper III, by methods not exceedingly influenced by the spherical symmetry hypothesis.     

Wilhelm Foerster and the development of solar and cosmical physics

Extracts from Foerster's papers relating to geomagnetism, solar and auroral physics are presented here so as to give an idea about his contribution to the solar-terrestrial physics during the years 1871-1906     

Considerations for the next generation of solar telescopes: A systems approach to solar physics

The exciting new high resolution images from the one meter Sunrise balloon telescope and the first images from the 1.6 meter Big Bear telescope together with the continuing data from the 1 meter Swedish Solar Observatory demonstrate the promise of the new generation of multimeter solar telescopes. While the promise of the new generation of telescopes is great the technical challenges to build them will require the efforts of a significant fraction of the solar community. In this talk I will emphasize the need for an integrated systems approach to the development of the telescope, its instruments, its software, and its operations and management structures. The experience of several decades of space mission has taught us a great deal about the value of planning mission development from the definition of the primary scientific objectives to the delivery of the data to the science community. Much of these lessons learned, often painfully, should provide guidance to those in developing the new telescope systems (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Recent progress of solar physics research in China

Owing to the largely improved facilities and working conditions,solar physics research in China has recently shown marked development.This paper reports on the recent progress of solar physics research in Mainland China,mainly focusing on several hot issues,including instrumentations,magnetic field observations and research,solar flares,filaments and their eruptions,coronal mass ejections and related processes,as well as active regions and the corona,small-scale phenomena,solar activity and its predictions....     

Keynote address: Outstanding problems in solar physics

Celebrating the diamond jubilee of the Physics Research Laboratory (PRL) in Ahmedabad, India, we look back over the last six decades in solar physics and contemplate on the ten outstanding problems (or research foci) in solar physics:

1. The solar neutrino problem
2. Structure of the solar interior (helioseismology)
3. The solar magnetic field (dynamo, solar cycle, corona)
4. Hydrodynamics of coronal loops
5. MHD oscillations and waves (coronal seismology)
6. The coronal heating problem
7. Self-organized criticality (from nanoflares to giant flares)
8. Magnetic reconnection processes
9. Particle acceleration processes
10. Coronal mass ejections and coronal dimming

The first two problems have been largely solved recently, while the other eight selected problems are still pending a final solution, and thus remain persistent Challenges for Solar Cycle 24, the theme of this jubilee conference.     

The Zeeman effect: applications to solar physics

This contribution is intended to give a brief review of some of the results concerning the Zeeman effect which have been recently published in the literature or which appear to be particularly relevant at the light of recent technological improvements in observations. The arguments emphasized are the Zeeman effect in molecular lines, the asymmetries observed in Stokes profiles from sunspots, and the interpretation of spectropolarimetric observations in the infrared.     

Quantum physics exploring gravity in the outer solar system: the SAGAS project

We summarise the scientific and technological aspects of the Search for Anomalous Gravitation using Atomic Sensors (SAGAS) project, submitted to ESA in June 2007 in response to the Cosmic Vision 2015–2025 call for proposals. The proposed mission aims at flying highly sensitive atomic sensors (optical clock, cold atom accelerometer, optical link) on a Solar System escape trajectory in the 2020 to 2030 time-frame. SAGAS has numerous science objectives in fundamental physics and Solar System science, for example numerous tests of general relativity and the exploration of the Kuiper belt. The combination of highly sensitive atomic sensors and of the laser link well adapted for large distances will allow measurements with unprecedented accuracy and on scales never reached before. We present the proposed mission in some detail, with particular emphasis on the science goals and associated measurements and technologies.     

Certain problems of solar and heliospheric physics in the light of novel satellite data

Recent satellite data have given a better insight into the possible nature of extremely strong disturbances on the Sun and in the heliosphere by relating them to processes in the solar interior. The energy, momentum, and mass transfer on various spatiotemporal scales are organized in the Sun into a hierarchy of coupled nonlinear processes. Confirmation has been given to the fact that coronal mass ejections and solar flares are not linked causally but merely reflect the existence of two channels of free-energy dissipation in the solar atmosphere in the form of plasma motion and plasma emission; their relative role can be described by a corresponding nondimensional parameter. Information on the global asymmetry of the solar emission and active processes has been gained. A great diversity in the geometry of eruptive events (not necessarily associated with magnetic reconnection) has been revealed. In our opinion, the basic unresolved problems in the investigation of solar activity dictate the necessity of carrying out more accurate, absolutely calibrated measurements of the whitelight solar emission at appropriately high spatiotemporal resolutions. The development of direct and indirect techniques of measuring the electric fields and currents with the aim of reconstructing the solar and heliospheric current system remains a challenging task.     

The solar physics Shuttle/Spacelab program and its relationship to studies of the flare build-up

Conclusion The Shuttle/Spacelab program offers an exciting and substantial opportunity for flight of sophisticated instruments for solar research in the 1980's. Problem-oriented missions composed of a number of instruments will be possible as well as flight opportunities for individual instruments developed quickly in response to new knowledge gained from earlier flights. The international scientific community has been asked to participate in defining new facility instruments that are needed. Announcements of Opportunities to participate in the development and use of these instruments will be made by NASA at the appropriate times.     

Gamma-ray,neutron, and hard X-ray studies and requirements for a high-energy solar physics facility

The requirements for future high-resolution spatial, spectral, and temporal observations of hard X-rays, gamma rays and neutrons from solar flares are discussed in the context of current high-energy flare observations. There is much promise from these observations for achieving a deep understanding of processes of energy release, particle acceleration and particle transport in a complicated environment such as the turbulent and highly magnetized atmosphere of the active Sun.