Solar Physics with the Square Kilometre Array

The Square Kilometre Array (SKA) will be the largest radio telescope ever built, aiming to provide collecting area larger than 1 km$^2$. The SKA will have two independent instruments, SKA-LOW comprising of dipoles organized as aperture arrays in Australia and SKA-MID comprising of dishes in South Africa. Currently the phase-1 of SKA, referred to as SKA1, is in its late design stage and construction is expected to start in 2020. Both SKA1-LOW (frequency range of 50-350 MHz) and SKA1-MID Bands 1, 2, and 5 (frequency ranges of 350-1050, 950-1760, and 4600-15300 MHz, respectively) are important for solar observations. In this paper we present SKA's unique capabilities in terms of spatial, spectral, and temporal resolution, as well as sensitivity and show that they have the potential to provide major new insights in solar physics topics of capital importance including (i) the structure and evolution of the solar corona, (ii) coronal heating, (iii) solar flare dynamics including particle acceleration and transport, (iv) the dynamics and structure of coronal mass ejections, and (v) the solar aspects of space weather. Observations of the Sun jointly with the new generation of ground-based and space-borne instruments promise unprecedented discoveries.Comment: Accepted for publication in Advances in Space Researc

What is the spatial distribution of magnetic helicity injected in a solar active region?

Copyright © 2006 EDP Sciences. This article appeared in Astronomy & Astrophysics 452 (2006) and may be found at http://www.aanda.org/index.php?option=article&access=doi&doi=10.1051/0004-6361:20054643Context. Magnetic helicity is suspected to play a key role in solar phenomena such as flares and coronal mass ejections. Several investigations have recently computed the photospheric flux of magnetic helicity in active regions. The derived spatial maps of the helicity flux density, called GA, have an intrinsic mixed-sign patchy distribution. Aims. Pariat et al. (2005) recently showed that GA is only a proxy of the helicity flux density, which tends to create spurious polarities. They proposed a better proxy, Gθ. We investigate here the implications of this new approach on observed active regions. Methods. The magnetic data are from MDI/SoHO instrument and the photospheric velocities are computed by local correlation tracking. Maps and temporal evolution of GA and Gθ are compared using the same data set for 5 active regions. Results. Unlike the usual GA maps, most of our Gθ maps show almost unipolar spatial structures because the nondominant helicity flux densities are significantly suppressed. In a few cases, the Gθ maps still contain spurious bipolar signals. With further modelling we infer that the real helicity flux density is again unipolar. On time-scales larger than their transient temporal variations, the time evolution of the total helicity fluxes derived from GA and Gθ show small differences. However, unlike GA, with Gθ the time evolution of the total flux is determined primarily by the predominant-signed flux while the nondominant-signed flux is roughly stable and probably mostly due to noise. Conclusions. Our results strongly support the conclusion that the spatial distribution of helicity injected into active regions is much more coherent than previously thought: on the active region scale the sign of the injected helicity is predominantly uniform. These results have implications for the generation of the magnetic field (dynamo) and for the physics of both flares and coronal mass ejections

Magnetic Helicity, Tilt, and Twist

The final publication is available at Springer via http://dx.doi.org/10.1007/s11214-014-0082-2Since its introduction to astro- and solar physics, the concept of helicity has proven to be useful in providing critical insights into physics of various processes from astrophysical dynamos, to magnetic reconnection and eruptive phenomena. Signature of helicity was also detected in many solar features, including orientation of solar active regions, or Joy’s law. Here we provide a summary of both solar phenomena and consider mutual relationship and its importance for the evolution of solar magnetic fields.European Union (European Social Fund—ESF)Greek national fundsScience and Technology Facilities Council (STFC)Hungarian Research grantsNAS

First high-resolution look at the quiet Sun with ALMA at 3 mm

We present an overview of high resolution quiet Sun observations, from disk center to the limb, obtained with the Atacama Large mm and sub-mm Array (ALMA) at 3 mm. Seven quiet Sun regions were observed with resolution of up to 2.5" by 4.5". We produced both average and snapshot images by self-calibrating the ALMA visibilities and combining the interferometric images with full disk solar images. The images show well the chromospheric network, which, based on the unique segregation method we used, is brighter than the average over the fields of view of the observed regions by $\sim 305$ K while the intranetwork is less bright by $\sim 280$ K, with a slight decrease of the network/intranetwork contrast toward the limb. At 3 mm the network is very similar to the 1600 \AA\ images, with somewhat larger size. We detected for the first time spicular structures, rising up to 15" above the limb with a width down to the image resolution and brightness temperature of $\sim$ 1800 K above the local background. No trace of spicules, either in emission or absorption, was found on the disk. Our results highlight ALMA's potential for the study of the quiet chromosphere.Comment: Astronomy and Astrophysics (Letters), in pres