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13,276
result(s) for
"Solar activity"
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Solar storms
Presents a range of views about the extent and type of damage that could result from solar storms. Proposed warning systems and other protective measures are also addressed.
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
Forecasting Solar Flares Using Magnetogram-based Predictors and Machine Learning
We propose a forecasting approach for solar flares based on data from Solar Cycle 24, taken by the
Helioseismic and Magnetic Imager
(HMI) on board the
Solar Dynamics Observatory
(SDO) mission. In particular, we use the Space-weather HMI Active Region Patches (SHARP) product that facilitates cut-out magnetograms of solar active regions (AR) in the Sun in near-realtime (NRT), taken over a five-year interval (2012 – 2016). Our approach utilizes a set of thirteen predictors, which are not included in the SHARP metadata, extracted from line-of-sight and vector photospheric magnetograms. We exploit several machine learning (ML) and conventional statistics techniques to predict flares of peak magnitude
>
M1
and
>
C1
within a 24 h forecast window. The ML methods used are multi-layer perceptrons (MLP), support vector machines (SVM), and random forests (RF). We conclude that random forests could be the prediction technique of choice for our sample, with the second-best method being multi-layer perceptrons, subject to an entropy objective function. A Monte Carlo simulation showed that the best-performing method gives accuracy
ACC
=
0.93
(
0.00
)
, true skill statistic
TSS
=
0.74
(
0.02
)
, and Heidke skill score
HSS
=
0.49
(
0.01
)
for
>
M1
flare prediction with probability threshold 15% and
ACC
=
0.84
(
0.00
)
,
TSS
=
0.60
(
0.01
)
, and
HSS
=
0.59
(
0.01
)
for
>
C1
flare prediction with probability threshold 35%.
Journal Article
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
Magnetic fields in the solar convection zone
It has been a prevailing picture that active regions on the solar surface originate from a strong toroidal magnetic field stored in the overshoot region at the base of the solar convection zone, generated by a deep seated solar dynamo mechanism. This article reviews the studies in regard to how the toroidal magnetic field can destabilize and rise through the convection zone to form the observed solar active regions at the surface. Furthermore, new results from the global simulations of the convective dynamos, and from the near-surface layer simulations of active region formation, together with helioseismic investigations of the pre-emergence active regions, are calling into question the picture of active regions as buoyantly rising flux tubes originating from the bottom of the convection zone. This article also gives a review on these new developments.
Journal Article
Extraterrestrial influence on climate change
An attempt is being made here to understand the influence of extraterrestrial activities as one of the important factors of climate change has been attempted here. The influence of Sun and distant stars on the environment of the earth has been studied during the cyclic changes in the Sun as well as episodic changes in the environment due to the effect of other celestial objects in between Sun-Earth environment. The study has been carried out based on the changes within the Sun as well as changes during the solar eclipse. During these extraterrestrial changes it has been observed that the earth changes in its atmosphere as well as geosphere, which may have local effect but the increase of these local effect in large scale may contribute to the climate change. Solar radiation drives atmospheric circulation. Since solar radiation represents almost all the energy available to the Earth, accounting for solar radiation and how it interacts with the atmosphere and the Earth's surface is fundamental to understanding the Earth's energy budget.
Book
Flare Prediction Using Photospheric and Coronal Image Data
The precise physical process that triggers solar flares is not currently understood. Here we attempt to capture the signature of this mechanism in solar-image data of various wavelengths and use these signatures to predict flaring activity. We do this by developing an algorithm that i) automatically generates features in 5.5 TB of image data taken by the
Solar Dynamics Observatory
of the solar photosphere, chromosphere, transition region, and corona during the time period between May 2010 and May 2014, ii) combines these features with other features based on flaring history and a physical understanding of putative flaring processes, and iii) classifies these features to predict whether a solar active region will flare within a time period of
T
hours, where
T
=
2
and
24
. Such an approach may be useful since, at the present time, there are no physical models of flares available for real-time prediction. We find that when optimizing for the True Skill Score (TSS), photospheric vector-magnetic-field data combined with flaring history yields the best performance, and when optimizing for the area under the precision–recall curve, all of the data are helpful. Our model performance yields a TSS of
0.84
±
0.03
and
0.81
±
0.03
in the
T
=
2
- and 24-hour cases, respectively, and a value of
0.13
±
0.07
and
0.43
±
0.08
for the area under the precision–recall curve in the
T
=
2
- and 24-hour cases, respectively. These relatively high scores are competitive with previous attempts at solar prediction, but our different methodology and extreme care in task design and experimental setup provide an independent confirmation of these results. Given the similar values of algorithm performance across various types of models reported in the literature, we conclude that we can expect a certain baseline predictive capacity using these data. We believe that this is the first attempt to predict solar flares using photospheric vector-magnetic field data as well as multiple wavelengths of image data from the chromosphere, transition region, and corona, and it points the way towards greater data integration across diverse sources in future work.
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
The Effect of “Rogue” Active Regions on the Solar Cycle
The origin of cycle-to-cycle variations in solar activity is currently the focus of much interest. It has recently been pointed out that large individual active regions with atypical properties can have a significant impact on the long-term behavior of solar activity. We investigate this possibility in more detail using a recently developed
2
×
2
D
dynamo model of the solar magnetic cycle. We find that even a single “rogue” bipolar magnetic region (BMR) in the simulations can have a major effect on the further development of solar activity cycles, boosting or suppressing the amplitude of subsequent cycles. In extreme cases, an individual BMR can completely halt the dynamo, triggering a grand minimum. Rogue BMRs also have the potential to induce significant hemispheric asymmetries in the solar cycle. To study the effect of rogue BMRs in a more systematic manner, a series of dynamo simulations were conducted, in which a large test BMR was manually introduced in the model at various phases of cycles of different amplitudes. BMRs emerging in the rising phase of a cycle can modify the amplitude of the ongoing cycle, while BMRs emerging in later phases will only affect subsequent cycles. In this model, the strongest effect on the subsequent cycle occurs when the rogue BMR emerges around cycle maximum at low latitudes, but the BMR does not need to be strictly cross-equatorial. Active regions emerging as far as
20
∘
from the equator can still have a significant effect. We demonstrate that the combined effect of the magnetic flux, tilt angle, and polarity separation of the BMR on the dynamo is
via
their contribution to the dipole moment,
δ
D
BMR
. Our results indicate that prediction of the amplitude, starting epoch, and duration of a cycle requires an accurate accounting of a broad range of active regions emerging in the previous cycle.
Journal Article