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"Sun: activity"
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Rebel star : our quest to solve the great mysteries of the sun
In 1869, a solar mystery was uncovered - astronomers observed a total solar eclipse, and for the first time saw the faint glow of the solar corona, the sun's outer atmosphere. Measurements of a previously unknown wavelength that made up this solar light sparked hot debate among scientists about its chemical components, and it wasn't until 1930 that scientists discovered that this wavelength was in fact iron being burned at 3,000,000 degrees Celsius. With the sun's surface at a mere 6,000 degrees C, the real mystery was born - what was heating the sun's corona? Our sun appeared to defy the laws of physics and nature. Since then, the sun has proved difficult to study, and its mysteries largely persist. But in summer 2018 and spring 2019, NASA and then the European Space Agency (ESA) are launching two of their most ambitious space missions to date, repeatedly diving closer to the sun than any previous spacecraft in history. These essential missions promise to provide important information about the sun's corona, and the unpredictable and destructive nature of solar wind. This timely and essential guide will examine our long-held fascination with the Red Giant, from ancient beliefs, to early scientific studies, right up to our present-day understanding, taking the lay reader on an absorbing and thrilling journey to the centre of our solar system.
Book
Solar Ultraviolet Bursts
The term “ultraviolet (UV) burst” is introduced to describe small, intense, transient brightenings in ultraviolet images of solar active regions. We inventorize their properties and provide a definition based on image sequences in transition-region lines. Coronal signatures are rare, and most bursts are associated with small-scale, canceling opposite-polarity fields in the photosphere that occur in emerging flux regions, moving magnetic features in sunspot moats, and sunspot light bridges. We also compare UV bursts with similar transition-region phenomena found previously in solar ultraviolet spectrometry and with similar phenomena at optical wavelengths, in particular Ellerman bombs. Akin to the latter, UV bursts are probably small-scale magnetic reconnection events occurring in the low atmosphere, at photospheric and/or chromospheric heights. Their intense emission in lines with optically thin formation gives unique diagnostic opportunities for studying the physics of magnetic reconnection in the low solar atmosphere. This paper is a review report from an International Space Science Institute team that met in 2016–2017.
Journal Article
The sun is kind of a big deal
A \"picture book from Awkward Yeti creator Nick Seluk [that] explains every part of the Sun's big job: keeping our solar system together, giving Earth day and night, keeping us warm, and more\"-- Provided by publisher.
Book
A Critical Assessment of the Flux Transport Dynamo
We first discuss how the flux transport dynamo with reasonably high diffusion can explain both the regular and the irregular features of the solar cycle quite well. Then, we critically examine the inadequacies of the model and the challenge posed by some recent observational data about meridional circulation, arriving at a conclusion that this model can still work within the bounds of observational data.
Journal Article
The science behind wonders of the sun : sun dogs, lunar eclipses, and green flash
\"Scientific explanations of natural phenomena caused by the Sun\"-- Provided by publisher.
Book
Decoding the Pre-Eruptive Magnetic Field Configurations of Coronal Mass Ejections
A clear understanding of the nature of the pre-eruptive magnetic field configurations of Coronal Mass Ejections (CMEs) is required for understanding and eventually predicting solar eruptions. Only two, but seemingly disparate, magnetic configurations are considered viable; namely, sheared magnetic arcades (SMA) and magnetic flux ropes (MFR). They can form via three physical mechanisms (flux emergence, flux cancellation, helicity condensation). Whether the CME culprit is an SMA or an MFR, however, has been strongly debated for thirty years. We formed an International Space Science Institute (ISSI) team to address and resolve this issue and report the outcome here. We review the status of the field across modeling and observations, identify the open and closed issues, compile lists of SMA and MFR observables to be tested against observations and outline research activities to close the gaps in our current understanding. We propose that the combination of multi-viewpoint multi-thermal coronal observations and multi-height vector magnetic field measurements is the optimal approach for resolving the issue conclusively. We demonstrate the approach using MHD simulations and synthetic coronal images.
Our key conclusion is that the differentiation of pre-eruptive configurations in terms of SMAs and MFRs seems artificial. Both observations and modeling can be made consistent if the pre-eruptive configuration exists in a hybrid state that is continuously evolving from an SMA to an MFR. Thus, the ‘dominant’ nature of a given configuration will largely depend on its evolutionary stage (SMA-like early-on, MFR-like near the eruption).
Journal Article
The Aditya-L1 mission of ISRO
The Aditya-L1 is the first space-based solar observatory of the Indian Space Research Organization (ISRO). The spacecraft will carry seven payloads providing uninterrupted observations of the Sun from the first Lagrangian point. Aditya-L1 comprises four remote sensing instruments, viz. a coronagraph observing in visible and infrared, a full disk imager in Near Ultra-Violet (NUV), and two full-sun integrated spectrometers in soft X-ray and hard X-ray. In addition, there are three instruments for in-situ measurements, including a magnetometer, to study the magnetic field variations during energetic events. Aditya-L1 is truly a mission for multi-messenger solar astronomy from space that will provide comprehensive observations of the Sun across the electromagnetic spectrum and in-situ measurements in a broad range of energy, including magnetic field measurements at L1.
Journal Article
Short-term periodicities in interplanetary, geomagnetic and solar phenomena during solar cycle 24
In this paper we study the quasi-periodic variations of sunspot area/number, 10.7 cm solar radio flux, Average Photospheric Magnetic Flux, interplanetary magnetic field (
B
z
) and the geomagnetic activity index
A
p
during the ascending phase of the current solar cycle 24. We use both Lomb-Scargle periodogram and wavelet analysis technique and find evidence for a multitude of quasi-periodic oscillations in all the data sets. In high frequency range (10 days to 100 days), both methods yield similar significance periodicities around 20–35 days and 45–60 days in all data sets. In the case of intermediate range, the significant periods were around 100–130 days, 140–170 days and 180–240 days The Morlet wavelet power spectrum shows that all of the above-mentioned periods are intermittent in nature. We find that the well-known “Rieger period” of (150–160 days) and near Rieger periods (130–190 days) were significant in both solar, interplanetary magnetic field and geomagnetic activity data sets during cycle 24. The geomagnetic activity is the result of the solar wind-magnetosphere interaction. Thus the variations in the detected periodicity in variety of solar, interplanetary and geomagnetic indices could be helpful to improve our knowledge of the inter-relationship between various processes in the Sun-Earth-Heliosphere system.
Journal Article