Found 4 talks width keyword solar activity

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Thursday December 11, 2014
Prof. Mats Carlsson
Institute of Theoretical Physics, University of Oslo

Abstract

Magnetic fields break through the solar surface in a hierarchy of magnetic elements ranging from Earth-sized sunspots down to tiny concentrations that are barely resolved in the highest-resolution photospheric images. In the chromosphere they combine in intricate, highly dynamic, and continuously evolving fibrilar patterns. Movements of the photospheric field-line footpoints drive, guide, and control the flows of energy and mass into the corona, and trigger energy-releasing magnetic reconnection through relentless topological rearrangement. The conversion from convectively driven footpoint motion to outer-atmosphere outflows and loading takes place in the dynamic, fine-structured chromosphere.

A number of important facilities for observing the solar chromosphere have recently come on line (e.g. the SDO and IRIS satellites and ground-based Fabry-Perot interferometers) or will become operational in the near future (e.g. DKIST). The overwhelming complexity of the chromosphere makes it necessary to have numerical simulations for the interpretation of the observations. Such realistic simulations, spanning the solar atmosphere from the convection zone to the corona, are now becoming feasible.

This presentation will introduce the fascinating aspects of chromospheric physics and review recent results from both observations and numerical simulations.


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Thursday May 13, 2010
Dr. Jorge Sánchez Almeida
Instituto de Astrofísica de Canarias, Spain

Abstract

We present a visual determination of the number of bright points (BPs) existing in the quiet Sun, which are structures though to trace intense kG magnetic concentrations. The measurement is based on a 0.1 arcsec angular resolution G-band movie obtained with the Swedish Solar Telescope at the solar disk center. We find 0.97 BPs/Mm2, which is a factor three larger than any previous estimate. It corresponds to 1.2 BPs per solar granule. Depending on the details of the segmentation, the BPs cover between 0.9% and 2.2% of the solar surface. Assuming their field strength to be 1.5 kG, the detected BPs contribute to the solar magnetic flux with an unsigned flux density between 13G and 33G. If network and inter-network regions are counted separately, they contain 2.2 BPs/Mm2 and 0.85 BPs/Mm2, respectively.

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Thursday April 29, 2010
Prof. Jack Harvey
National Solar Observatory, USA

Abstract

The Sun presents us with many unsolved mysteries. In this talk I discuss three of them that have intrigued me for the last 50 years. Solar flares are the most powerful explosions in space between here and the nearby stars. The only viable power source is stored magnetic energy. Yet definitive observations of changes in the magnetic field associated with flares have been lacking until recently. Measurements with the GONG network have helped to address this mystery and the results are surprising. Efforts to observe the weak magnetic fields in the solar photosphere date nearly to the discovery of magnetism on the Sun. Improvements in observational capabilities have made this area a 'hot' topic with many important contributions from people at the IAC. High resolution observations are clarifying many features. I will focus on the role played by lower resolution work in defining the uniformity of the still mysterious weak magnetic fields over large spatial and temporal scales. Physics changes from hydrodynamic to magnetic dominance as one moves upward from the photosphere to the chromosphere. This leads to significant and complicated changes in the magnetic field in both the active and quiet Sun. Observations of the chromospheric magnetic field show several unexpected and mysterious features. Solving these mysteries will be an exciting area as observational and spectral inversion capabilities develop.

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Tuesday April 27, 2010
Dr. María Jesús Martínez González
Instituto de Astrofísica de Canarias, Spain

Abstract

The quiet Sun (the 99%, or more, of the solar surface not covered by sunspots or active regions) is receiving increased attention in recent years; its role on the global magnetism and its complexity are being increasingly recognised. A picture of a rather stochastic quiet Sun magnetism is emerging. From these recent works, the quiet Sun magnetism is presented as a myriad of magnetic field vectors having an isotropical distribution with a cascade of scales down to the mean free path of the photon. But this chaotic representation also shows clear signs of intermittency: at a low frequency rate (0.022 events h-1 arcsec-2) the magnetic field appear in the quiet Sun forming well-organised loop structures at granular scales. More interesting, these loops rise to higher layers and their energy input into the chromosphere can be important for the heating of this layer. In the talk, I will present a pedagogic view of the quiet Sun magnetism. I will focus on the ascent of the smallest ever observed magnetic flux emergence through the solar atmosphere. More specifically, I will show how to infer from high resolution, spectro-polarimetric observations (taken with the SOT instrument onboard Hinode) the magnetic topology of the fields, how they rise through the photosphere to the chromosphere, and the implications of this phenomena for chromospheric (and coronal) heating.


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