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Title: The infrared colours of the Sun
Authors: L. Casagrande, I. Ramirez, J. Melendez, M. Asplund

Solar infrared colours provide powerful constraints on the stellar effective temperature scale, but to this purpose they must be measured with both accuracy and precision. We achieve this requirement by using line-depth ratios to derive in a model independent way the infrared colours of the Sun, and use the latter to test the zero-point of the Casagrande et al. (2010) effective temperature scale, confirming its accuracy. Solar colours in the widely used 2MASS -J H K- and WISE -W1 W2 W3 W4- systems are provided. A cross check of the effective temperatures derived implementing 2MASS or WISE magnitudes in the infrared flux method confirms that the absolute calibration of the two systems agree within the errors, possibly suggesting a 1% offset between the two, thus validating extant near and mid infrared absolute calibrations. While 2MASS magnitudes are usually well suited to derive effective temperatures, we find that a number of solar like stars exhibit anomalous WISE colours. In most cases this effect is spurious and traceable to lower quality measurements, although for a couple of objects (3 ± 2 % of the total sample) it might be real and hints towards the presence of warm/hot debris disks.

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Corona
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Title: Newly Discovered Global Temperature Structures in the Quiet Sun at Solar Minimum
Authors: Zhenguang Huang, Richard A. Frazin, Enrico Landi, Ward B. Manchester IV, Alberto M. Vásquez, Tamas I. Gombosi

Magnetic loops are building blocks of the closed-field corona. While active region loops are readily seen in images taken at EUV and X-ray wavelengths, quiet Sun loops are seldom identifiable and therefore difficult to study on an individual basis. The first analysis of solar minimum (Carrington Rotation 2077) quiet Sun (QS) coronal loops utilizing a novel technique called the Michigan Loop Diagnostic Technique (MLDT) is presented. This technique combines Differential Emission Measure Tomography (DEMT) and a potential field source surface (PFSS) model, and consists of tracing PFSS field lines through the tomographic grid on which the Local Differential Emission Measure (LDEM) is determined. As a result, the electron temperature Te and density Ne at each point along each individual field line can be obtained. Using data from STEREO/EUVI and SOHO/MDI, the MLDT identifies two types of QS loops in the corona: so-called "up" loops in which the temperature increases with height, and so-called "down" loops in which the temperature decreases with height. Up loops are expected, however, down loops are a surprise, and furthermore, they are ubiquitous in the low-latitude corona. Up loops dominate the QS at higher latitudes. The MLDT allows independent determination of the empirical pressure and density scale heights, and the differences between the two remain to be explained. The down loops appear to be a newly discovered property of the solar minimum corona that may shed light on the physics of coronal heating. The results are shown to be robust to the calibration uncertainties of the EUVI instrument.

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Sun is the most perfect sphere ever observed in nature

The sun is the most perfectly round natural object known in the universe, say scientists who have conducted precise measurements of its dimensions.
As a spinning ball of gas, astronomers had always expected our nearest star to bulge slightly at its equator, making it very slightly flying-saucer shaped. The planet Jupiter demonstrates this effect well. Its high rate of spin - once every 10 hours - means that it is almost 7% wider across its equator than the distance from pole to pole.

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Title: The Role of Type II Spicules in the Upper Solar Atmosphere
Authors: J. A. Klimchuk

We examine the suggestion that most of the hot plasma in the Sun's corona comes from type II spicule material that is heated as it is ejected from the chromosphere. This contrasts with the traditional view that the corona is filled via chromospheric evaporation that results from coronal heating. We explore the observational consequences of a hypothetical spicule dominated corona and conclude from the large discrepancy between predicted and actual observations that only a small fraction of the hot plasma can be supplied by spicules (<2% in active regions and <5% in the quiet Sun). The red-blue asymmetries of EUV spectral lines and the ratio of lower transition region (LTR; T<0.1 MK) to coronal emission measures are both predicted to be 2 orders of magnitude larger than observed. Furthermore, hot spicule material would cool dramatically by adiabatic expansion as it rises into the corona, so coronal heating would be required to maintain the high temperatures that are seen at all altitudes. The necessity of coronal heating is inescapable. Traditional coronal heating models predict far too little emission from the LTR, and we suggest that this emission comes primarily from the bulk of the spicule material that is heated to <0.1 MK and is visible in He II (304 A) as it falls back to the surface.

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New light shed on explosive solar activity

The first images of an upward surge of the Sun's gases into quiescent coronal loops have been identified by an international team of scientists. The discovery is one more step towards understanding the origins of extreme space storms, which can destroy satellite communications and damage power grids on Earth.
The study published today by University of Cambridge scientists working with colleagues in India and the USA is the first to visualise the movement of gases at one million degrees in coronal loops - solar structures that are rooted at both ends and extend out from active regions of the Sun. Active regions are the 'cradle' for explosive energy releases such as solar flares and coronal mass ejections (CMEs).

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NI scientist makes solar tornado breakthrough

A Northern Ireland man is one of a team of scientists who have made a groundbreaking discovery about tornadoes on the surface of the sun.
Dr Eamon Scullion from County Antrim, and a team at the University of Oslo have solved an important piece of a long-standing puzzle in astrophysics.
It involves magnetic tornadoes which swirl at speeds of 1,100 km per hour on the surface of the sun.

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Space tornadoes power the atmosphere of the Sun

The super tornadoes - which are thousands of times larger and more powerful than their earthly counterparts but which have a magnetic skeleton - spin at speeds of more than 6,000 mph at temperatures in millions of centigrade in the Sun's atmosphere.
They are more than 1,000 miles wide - hundreds of miles longer than the total distance between Land's End to John O'Groats. It is estimated that there are as many as 11,000 of these swirling events above the Suns surface at any time.

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Title: Dead calm areas in the very quiet Sun
Authors: M. J. Martínez González, R. Manso Sainz, A. Asensio Ramos, E. Hijano

We analyse two regions of the quiet Sun (35.6 x 35.6 Mm^2) observed at high spatial resolution (~100 km) in polarised light by the IMaX spectropolarimeter onboard the Sunrise balloon. We identify 497 small-scale (~400 km) magnetic loops, appearing at an effective rate of 0.25 loop h^{-1} arcsec^{-2}; further, we argue that this number and rate are underestimated by ~30%. However, we find that these small dipoles do not appear uniformly on the solar surface: their spatial distribution is rather filamentary and clumpy, creating dead calm areas, characterised by a very low magnetic signal and a lack of organised loop-like structures at the detection level of our instruments, that cannot be explained as just statistical fluctuations of a Poisson spatial process. We argue that this is an intrinsic characteristic of the mechanism that generates the magnetic fields in the very quiet Sun. The spatio-temporal coherences and the clumpy structure of the phenomenon suggest a recurrent, intermittent mechanism for the generation of magnetic fields in the quietest areas of the Sun.

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 Polar Field Reversal as observed with Hinode 

The international research team led by Saku Tsuneta, a professor at NAOJ, has been performing the monthly polar observations with Hinode from September 2008. We here report the discovery that the average magnetic flux of the north polar region is rapidly and steadily decreasing during the period of 2008 and 2012. The reversal (from minus to plus polarity) is taking place in sequence from lower latitude to higher latitude. The average magnetic flux of the polar region soon becomes zero. The estimated completion of the reversal of the north polar region will take place in 1 months or so, about one year earlier than the nominal expected reversal time. 

The polarity of the extended uni-polar magnetic field in the solar polar region is known to reverse every 11 years, and the reversal occurs at around the maximum of solar activity, which is expected to take place at around 2013 May (NOAA ).
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Title: The faint young Sun problem
Authors: Georg Feulner

For more than four decades, scientists have been trying to find an answer to one of the most fundamental questions in paleoclimatology, the `faint young Sun problem'. For the early Earth, models of stellar evolution predict a solar energy input to the climate system which is about 25% lower than today. This would result in a completely frozen world over the first two billion years in the history of our planet, if all other parameters controlling Earth's climate had been the same. Yet there is ample evidence for the presence of liquid surface water and even life in the Archean (3.8 to 2.5 billion years before present), so some effect (or effects) must have been compensating for the faint young Sun. A wide range of possible solutions have been suggested and explored during the last four decades, with most studies focusing on higher concentrations of atmospheric greenhouse gases like carbon dioxide, methane or ammonia. All of these solutions present considerable difficulties, however, so the faint young Sun problem cannot be regarded as solved. Here I review research on the subject, including the latest suggestions for solutions of the faint young Sun problem and recent geochemical constraints on the composition of Earth's early atmosphere. Furthermore, I will outline the most promising directions for future research. In particular I would argue that both improved geochemical constraints on the state of the Archean climate system and numerical experiments with state-of-the-art climate models are required to finally assess what kept the oceans on the Archean Earth from freezing over completely.

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Ed ~ It has been shown that the atmospheric pressure of the Early Earth was between 0.6 to 1.6 atmospheres, and very likely close to today's atmosphere - so the current focus is on the chemistry of the atmosphere of the Early Earth, namely the very efficient greenhouse gases nitrous oxide and methane.



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