A pinboard by
Bhishek Manek

Graduate Student, University of California, Santa Cruz


Solar Magnetic Fields and its Dynamics

Sun in famously known as the Rosetta stone of Astronomy and is one of the most extensively studied astronomical objects. It offers the opportunity to understand the physical processes in the interior of stars in a greater detail. Observational, theoretical and numerical studies over the past few decades have significantly improved our understanding but it is astonishing to note that there stands a wide gap between the observations and theoretical understanding. One of the most important and dynamical characteristics of Sun, and in general Stars, is their magnetic field. Sun is a hot ball of plasma (ionized gas) with ubiquitous presence of magnetic field all through the solar atmosphere. One of the important outstanding problems in the study of Sun (and in general stars) is about the origin and sustenance of magnetic fields against diffusion which tends to decay the magnetic fields over a period of time. It is believed that magnetic field formation in the stars takes place by a dynamo process which comprises of generation, transport, decay by diffusion and further re-generation of magnetic fields. A substantial element of all the current potential paradigms for the operation of the solar dynamo is the rise of magnetic “flux tubes” from their point of amplification in the interior of the Sun to the outer atmosphere. Vast majority of work in this regard has focused on the rise of an isolated magnetic entity in an otherwise field-free atmosphere which are quite unrealistic constraints and do not capture the real picture of transport of magnetic fields. Isolated magnetic structures are unrealistic and artificially impose unnecessary constraints on its dynamics. The topology of realistic magnetic fields is much more complex and may have different dynamics. My research focuses on examining the consequences of relaxing these constraints. Even in this extremely simple situation, the initial results are startling. Extending this model to 3D can potentially alter the way transport of flux tubes is accounted in solar dynamo models. Study of rise of magnetic flux tubes also gives an important insight into the surface magnetic fields of Sun which potentially governs all the observed high energy phenomenon like solar flares etc. Study of such high energy phenomenon on the Sun has profound impact on installation of satellites in outer space, electrical grid networks on Earth and even space travel.


A History of Solar Activity over Millennia

Abstract: Presented here is a review of present knowledge of the long-term behavior of solar activity on a multi-millennial timescale, as reconstructed using the indirect proxy method. The concept of solar activity is discussed along with an overview of the special indices used to quantify different aspects of variable solar activity, with special emphasis upon sunspot number.Over long timescales, quantitative information about past solar activity can only be obtained using a method based upon indirect proxies, such as the cosmogenic isotopes 14C and 10Be in natural stratified archives (e.g., tree rings or ice cores). We give an historical overview of the development of the proxy-based method for past solar-activity reconstruction over millennia, as well as a description of the modern state. Special attention is paid to the verification and cross-calibration of reconstructions. It is argued that this method of cosmogenic isotopes makes a solid basis for studies of solar variability in the past on a long timescale (centuries to millennia) during the Holocene.A separate section is devoted to reconstructions of strong solar energetic-particle (SEP) events in the past, that suggest that the present-day average SEP flux is broadly consistent with estimates on longer timescales, and that the occurrence of extra-strong events is unlikely.Finally, the main features of the long-term evolution of solar magnetic activity, including the statistics of grand minima and maxima occurrence, are summarized and their possible implications, especially for solar/stellar dynamo theory, are discussed.

Pub.: 21 Mar '13, Pinned: 30 Jun '17