Photospheric Magnetic Field: Relationship Between North–South Asymmetry and Flux Imbalance

Photospheric magnetic fields were studied using the Kitt Peak synoptic maps for 1976?–?2003. Only strong magnetic fields (B>100 G) of the equatorial region were taken into account. The north–south asymmetry of the magnetic fluxes was considered as well as the imbalance between positive and negative fluxes. The north–south asymmetry displays a regular alternation of the dominant hemisphere during the solar cycle: the northern hemisphere dominated in the ascending phase, the southern one in the descending phase during Solar Cycles 21?–?23. The sign of the imbalance did not change during the 11 years from one polar-field reversal to the next and always coincided with the sign of the Sun’s polar magnetic field in the northern hemisphere. The dominant sign of leading sunspots in one of the hemispheres determines the sign of the magnetic-flux imbalance. The sign of the north–south asymmetry of the magnetic fluxes and the sign of the imbalance of the positive and the negative fluxes are related to the quarter of the 22-year magnetic cycle where the magnetic configuration of the Sun remains constant (from the minimum where the sunspot sign changes according to Hale’s law to the magnetic-field reversal and from the reversal to the minimum). The sign of the north–south asymmetry for the time interval considered was determined by the phase of the 11-year cycle (before or after the reversal); the sign of the imbalance of the positive and the negative fluxes depends on both the phase of the 11-year cycle and on the parity of the solar cycle. The results obtained demonstrate the connection of the magnetic fields in active regions with the Sun’s polar magnetic field in the northern hemisphere.     

3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum

Measurement of the coronal magnetic field is a crucial ingredient in understanding the nature of solar coronal phenomena at all scales. We employed STEREO/COR1 data obtained during a deep minimum of solar activity in February 2008 (Carrington Rotation CR 2066) to retrieve and analyze the three-dimensional (3D) coronal electron density in the range of heights from 1.5 to 4 R_⊙ using a tomography method. With this, we qualitatively deduced structures of the coronal magnetic field. The 3D electron-density analysis is complemented by the 3D STEREO/EUVI emissivity in the 195 Å band obtained by tomography for the same CR. A global 3D MHD model of the solar corona was used to relate the reconstructed 3D density and emissivity to open/closed magnetic-field structures. We show that the density-maximum locations can serve as an indicator of current-sheet position, while the locations of the density-gradient maximum can be a reliable indicator of coronal-hole boundaries. We find that the magnetic-field configuration during CR 2066 has a tendency to become radially open at heliocentric distances greater than 2.5 R_⊙. We also find that the potential-field model with a fixed source surface is inconsistent with the boundaries between the regions with open and closed magnetic-field structures. This indicates that the assumption of the potential nature of the coronal global magnetic field is not satisfied even during the deep solar minimum. Results of our 3D density reconstruction will help to constrain solar coronal-field models and test the accuracy of the magnetic-field approximations for coronal modeling.     

High-Resolution Optical Spectroscopy of the Post-AGB Supergiant V340 Ser ( $${\mathbf{=}}$$ IRAS 17279 $$\mathbf{-}$$ 1119)

Astronomy Letters - Evidence of wind variability and velocity stratification in the extended atmosphere has been found in the spectra of the supergiant V340 Ser ( $${=}$$ IRAS 17279 $$-$$ 1119)...     

Precursor heating and acceleration by Langmuir waves: The type II Supernova case

The effect of shock wave propagation is investigated with respect to precursor heating and acceleration, upstream, with the aim of explaining Supernova (SN) observations.A model is presented, where two different sources of Langmuir waves produce upstream heating and acceleration: (1) Langmuir waves excited by resonance beam particles, that are accelerated through the shock front by Bell's mechanism; and (2) Langmuir waves, created in the post-shock turbulent zone.The most important processes considered in the calculations are: (1) the heating efficiency of beam particles of different velocity; (2) Bell's acceleration efficiency; (3) the spectrum of Langmuir waves created in a turbulent regime; (4) the effects of density, and of the density gradient in the medium, where the shock propagates.The calculations are applied to type II SN. The results show that temperatures of 10⁵–10⁶ K, obtained in the preshock region, can explain P-Cygni observed line profiles. Moreover, accelerations of the plasma in front of the shock up tov10⁸ cm s^–1 by momentum exchange, are in good agreement with observations.Partially supported by Conselho Nacional de Desenvolvimento Cientifico e Technológico (CNPq) and Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP).     

Identification of Possible Intense Historical Solar Storms During the Years 1781–1788 Inferred from Aurorae and Geomagnetic Observations in Rio De Janeiro

The reconstruction of solar activity during the late 18th century is a puzzle for researchers due to the scarcity of sunspot observations in that epoch. In this work, we analyse some details of the solar activity during the years 1781–1788, inferred from geomagnetic measurements and visual observations of aurorae performed by the Portuguese scientist Bento Sanches Dorta from Rio de Janeiro. We describe in greater detail four large solar storms that induced large changes in daily values of geomagnetic declination and, simultaneously, correspond to visual observations of aurorae described by Sanches Dorta.     

Possibility of Excitation of Low-ℓ P-Modes by Energetic Solar Transients

We examine the temporal variation of power in low-ℓ modes using GONG data for the period of May 1995–October 2005 and compare this with disk-integrated flare and CME indices. A poor correlation between the running means of Flare Index and mode power is found. A similar result is found for CME Index also. Variations in the running mean mode power corresponding to ℓ = 0 modes with different radial orders are generally stochastic in nature. This behaviour is also reflected in the distribution of mode power.     

Average nocturnal and seasonal variations of sodium nightglow at 23°S, 46°W

The seasonal variation of the nocturnal average intensity, and the typical variation of the sodium airglow intensity during the night have been deduced, using a data set that has been accumulated over a period of 5 years. The maximum intensity, which occurs at the equinoxes, is about 2–3 times as large as the intensity during winter, when the intensity of the D₂ line is about 30 R. The nocturnal variation is symmetrical about midnight, where the intensity is some 30% less than just after (before) dusk (dawn) values.     

User's guide to REDUCE subroutines for algebraic computations in general relativity

We describe the use of a package of subroutines for general-relativistic algebraic computations written in the LISP-based algebraic programming system REDUCE developed by Anthony Hearn. The first group of routines calculates concomitants of the metric tensor such as the Riemann tensor, Ricci tensor, Ricci scalar, Einstein tensor and Weyl tensor from given covariant or covariant and contravariant metric tensor components. One of these procedures includes the evaluation of the Maxwell equations and invariants as well as the Maxwell energy momentum tensor. A second group of routines takes the components of a null tetrad as input and evaluates the null frame projections of the Riemann tensor, the Einstein tensor as well as – if required – the 14 local invariants of the Riemann tensor. It also includes a determination of the Petrov type. Perturbation calculations may be performed and run effectively. The output can be presented in a flexible format chosen according to the needs of the user. A number of further special-purpose programs are available on request. The article should enable a reader familar with General Relativity but unfamilar with formula manipulating system, to employ the package.