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Title: Dimming of the Mid-20th Century Sun
Author: Peter Foukal

Advances in understanding of the white light faculae measured at the Royal Greenwich Observatory from 1874 to 1976 suggest that they offer a more direct measure of solar brightening by small diameter photospheric magnetic flux tubes than do chromospheric proxies. Proxies such as the area of Ca K plages, the Mg index or the microwave flux include many dark photospheric structures as well as pores and sunspots. Our reconstruction of variation in total solar irradiance,TSI,based on the faculae indicates that the sun dimmed by almost 0.1 percent in the mid- twentieth century rather than brightening as represented in previous reconstructions. This dimmimg at the sun's highest activity level since the seventeenth century is consistent with the photometric behaviour observed in somewhat younger sun like stars. The prolonged TSI decrease may have contributed more to the cooling of climate between about 1940 and 1970 than present models indicate.

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Title: Modelling total solar irradiance since 1878 from simulated magnetograms
Author: M. Dasi-Espuig, J. Jiang, N. A. Krivova, S. K. Solanki

We present a new model of total solar irradiance (TSI) based on magnetograms simulated with a surface flux transport model (SFTM) and the SATIRE (Spectral And Total Irradiance REconstructions) model. Our model provides daily maps of the distribution of the photospheric field and the TSI starting from 1878. We first calculate the magnetic flux on the solar surface emerging in active and ephemeral regions. The evolution of the magnetic flux in active regions is computed using a surface flux transport model fed with the observed record of sunspot group areas and positions. The magnetic flux in ephemeral regions is treated separately using the concept of overlapping cycles. To model the ephemeral region cycles, we assume that their length and amplitude are related to that of the sunspot cycles. We then use a version of the SATIRE model to compute the TSI. The area coverage and the distribution of different magnetic features as a function of time, which are required by SATIRE, are extracted from the simulated magnetograms and the modelled ephemeral region magnetic flux. Previously computed intensity spectra of the various types of magnetic features are employed. Our model reproduces the PMOD composite of TSI measurements starting from 1978 at daily and rotational timescales more accurately than the previous version of the SATIRE model computing TSI over this period of time. The simulated magnetograms provide a more realistic representation of the evolution of the magnetic field on the photosphere and also allow us to make use of information on the spatial distribution of the magnetic fields before the times when observed magnetograms were available. We find that the secular increase in TSI since 1878 is fairly stable to modifications of the treatment of the ephemeral region magnetic flux.

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Why NASA Studies the Ultraviolet Sun

"Ultraviolet light from the sun can show us the origins of solar storms that can lead to power outages, cell phone disruptions, and delays in shipping packages due to the rerouting of planes from over the pole" - Joseph Gurman, project scientist for both the Solar and Heliospheric Observatory and the Solar Terrestrial Relations Observatory at Goddard.
By understanding what occurs in the suns atmosphere, scientists hope to predict when powerful solar events such as coronal mass ejections and solar flares may occur.

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Title: Spectral atlases of the Sun from 3980 to 7100 angstroms at the center and at the limb
Author: Hassan Fathivavsari, Ali Ajabshirizadeh, Serge Koutchmy

In this work, we present digital and graphical atlases of spectra of both the solar disk-center and of the limb near the Solar poles using data taken at the UTS-IAP & RIAAM (the University of Tabriz Siderostat, telescope and spectrograph jointly developed with the Institut d'Astrophysique de Paris and Research Institute for Astronomy and Astrophysics of Maragha). High resolution and high signal-to-noise ratio (SNR)CCD-slit spectra of the sun for 2 different parts of the disk, namely for ~=~1.0 (solar center) \& for ~=~ 0.3 solar limb) are provided and discussed. While there are several spectral atlases of the solar disk-center, this is the first spectral atlas ever produced for the solar limb at this spectral range. The resolution of the spectra is about {R}~~~70 000 (\Delta\lambda~~~0.09 {\AA} with the signal-to-noise ratio (SNR) of 400-600. The full atlas covers the 3980 to 7100 {\AA} spectral regions and contains 44 pages with three partial spectra of the solar spectrum put on each page to make it compact. The difference spectrum of the normalised solar disk-center and the solar limb is also included in the graphic presentation of the atlas to show the difference of line profiles, including far wings. The identification of the most significant solar lines is included in the graphic presentation of the atlas. Telluric lines are producing a definite signature on the difference spectra which is easy to notice. At the end of this paper we present only two sample pages of the whole atlas while the graphic presentation of the whole atlas along with its ASCII file can be accessed via the ftp server of the CDS in Strasbourg via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via this link http://cdsarc.u-strasbg.fr/viz-bin/qcat?J/other/ApSS.

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Title: Evidence for distinct modes of solar activity
Author: I.G. Usoskin, G. Hulot, Y. Gallet, R. Roth, A. Licht, F. Joos, G. A. Kovaltsov, E. Thebault, A. Khokhlov

Aims. The Sun shows strong variability in its magnetic activity, from Grand minima to Grand maxima, but the nature of the variability is not fully understood, mostly because of the insufficient length of the directly observed solar activity records and of uncertainties related to long-term reconstructions. Here we present a new adjustment-free reconstruction of solar activity over three millennia and study its different modes.
Methods. We present a new adjustment-free, physical reconstruction of solar activity over the past three millennia, using the latest verified carbon cycle, 14C production, and archeomagnetic field models. This great improvement allowed us to study different modes of solar activity at an unprecedented level of details.
Results. The distribution of solar activity is clearly bi-modal, implying the existence of distinct modes of activity. The main regular activity mode corresponds to moderate activity that varies in a relatively narrow band between sunspot numbers about 20 and 67. The existence of a separate Grand minimum mode with reduced solar activity, which cannot be explained by random fluctuations of the regular mode, is confirmed at a high confidence level. The possible existence of a separate Grand maximum mode is also suggested, but the statistics is too low to reach a confident conclusion.
Conclusions. The Sun is shown to operate in distinct modes - a main general mode, a Grand minimum mode corresponding to an inactive Sun, and a possible Grand maximum mode corresponding to an unusually active Sun. These results provide important constraints for both dynamo models of Sun-like stars and investigations of possible solar influence on Earth's climate.

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Title: Giant Convection Cells Found on the Sun
Author: David H. Hathaway, Lisa Upton, Owen Colegrove

Heat is transported through the outermost 30% of the Sun's interior by overturning convective motions. These motions are evident at the Sun's surface in the form of two characteristic cellular structures - granules and supergranules (~1000 and ~30,000 km across respectively). The existence of much larger cells has been suggested by both theory and observation for over 45 years. We found evidence for giant cellular flows that persist for months by tracking the motions of supergranules. As expected from the effects of the Sun's rotation, the flows in these cells are clockwise around high pressure in the north, counter-clockwise in the south and transport angular momentum toward the equator, maintaining the Sun's rapid equatorial rotation.

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Stanford solar scientists solve one of the sun's mysteries

Stanford solar scientists have solved one of the few remaining fundamental mysteries of how the sun works.
The mechanism, known as meridional flow, works something like a conveyor belt. Magnetic plasma migrates north to south on the sun's surface, from the equator to the poles, and then cycles into the sun's interior on its way back to the equator.

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NASA Telescope Observes How Sun Stores and Releases Energy

A NASA suborbital telescope has given scientists the first clear evidence of energy transfer from the sun's magnetic field to the solar atmosphere or corona. This process, known as solar braiding, has been theorized by researchers, but remained unobserved until now.
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Title: Can Superflares Occur on Our Sun?
Authors: Kazunari Shibata, Hiroaki Isobe, Andrew Hillier, Arnab Rai Choudhuri, Hiroyuki Maehara, Takako T. Ishii, Takuya Shibayama, Shota Notsu, Yuta Notsu, Takashi Nagao, Satoshi Honda, Daisaku Nogami

Recent observations of solar type stars with the Kepler satellite by Maehara et al. have revealed the existence of superflares (with energy of 10^33 - 10^35 erg) on Sun-like stars, which are similar to our Sun in their surface temperature (5600 K - 6000 K) and slow rotation (rotational period > 10 days). From the statistical analysis of these superflares, it was found that superflares with energy 10^34 erg occur once in 800 years and superflares with 10^35 erg occur once in 5000 years on Sun-like stars. In this paper, we examine whether superflares with energy of 10^33 - 10^35 erg could occur on the present Sun through the use of simple order-of-magnitude estimates based on current ideas relating to the mechanisms of the solar dynamo.

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Title: Torsional Oscillations in a Global Solar Dynamo
Authors: P. Beaudoin, P. Charbonneau, E. Racine, P.K. Smolarkiewicz

We characterise and analyse rotational torsional oscillations developing in a large-eddy magnetohydrodynamical simulation of solar convection (Ghizaru, Charbonneau, and Smolarkiewicz, Astrophys. J. Lett., 715, L133 (2010); Racine et al., Astrophys. J., 735, 46 (2011)) producing an axisymmetric large-scale magnetic field undergoing periodic polarity reversals. Motivated by the many solar-like features exhibited by these oscillations, we carry out an analysis of the large-scale zonal dynamics. We demonstrate that simulated torsional oscillations are not driven primarily by the periodically-varying large-scale magnetic torque, as one might have expected, but rather via the magnetic modulation of angular-momentum transport by the large-scale meridional flow. This result is confirmed by a straightforward energy analysis. We also detect a fairly sharp transition in rotational dynamics taking place as one moves from the base of the convecting layers to the base of the thin tachocline-like shear layer formed in the stably stratified fluid layers immediately below. We conclude by discussing the implications of our analyses with regards to the mechanism of amplitude saturation in the global dynamo operating in the simulation, and speculate on the possible precursor value of torsional oscillations for the forecast of solar cycle characteristics.

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