2,456 research outputs found
Evidence for Partial Taylor Relaxation from Changes in Magnetic Geometry and Energy during a Solar Flare
Solar flares are powered by energy stored in the coronal magnetic field, a
portion of which is released when the field reconfigures into a lower energy
state. Investigation of sunspot magnetic field topology during flare activity
is useful to improve our understanding of flaring processes. Here we
investigate the deviation of the non-linear field configuration from that of
the linear and potential configurations, and study the free energy available
leading up to and after a flare. The evolution of the magnetic field in NOAA
region 10953 was examined using data from Hinode/SOT-SP, over a period of 12
hours leading up to and after a GOES B1.0 flare. Previous work on this region
found pre- and post-flare changes in photospheric vector magnetic field
parameters of flux elements outside the primary sunspot. 3D geometry was thus
investigated using potential, linear force-free, and non-linear force-free
field extrapolations in order to fully understand the evolution of the field
lines. Traced field line geometrical and footpoint orientation differences show
that the field does not completely relax to a fully potential or linear
force-free state after the flare. Magnetic and free magnetic energies increase
significantly ~ 6.5-2.5 hours before the flare by ~ 10^31 erg. After the flare,
the non-linear force-free magnetic energy and free magnetic energies decrease
but do not return to pre-flare 'quiet' values. The post-flare non-linear
force-free field configuration is closer (but not equal) to that of the linear
force-free field configuration than a potential one. However, the small degree
of similarity suggests that partial Taylor relaxation has occurred over a time
scale of ~ 3-4 hours.Comment: Accepted for Publication in Astronomy & Astrophysics. 11 pages, 11
figure
Automated Coronal Hole Identification via Multi-Thermal Intensity Segmentation
Coronal holes (CH) are regions of open magnetic fields that appear as dark
areas in the solar corona due to their low density and temperature compared to
the surrounding quiet corona. To date, accurate identification and segmentation
of CHs has been a difficult task due to their comparable intensity to local
quiet Sun regions. Current segmentation methods typically rely on the use of
single EUV passband and magnetogram images to extract CH information. Here, the
Coronal Hole Identification via Multi-thermal Emission Recognition Algorithm
(CHIMERA) is described, which analyses multi-thermal images from the
Atmospheric Image Assembly (AIA) onboard the Solar Dynamics Observatory (SDO)
to segment coronal hole boundaries by their intensity ratio across three
passbands (171 \AA, 193 \AA, and 211 \AA). The algorithm allows accurate
extraction of CH boundaries and many of their properties, such as area,
position, latitudinal and longitudinal width, and magnetic polarity of
segmented CHs. From these properties, a clear linear relationship was
identified between the duration of geomagnetic storms and coronal hole areas.
CHIMERA can therefore form the basis of more accurate forecasting of the start
and duration of geomagnetic storms
Fields and Flares: Understanding the Complex Magnetic Topologies of Solar Active Regions
Sunspots are regions of decreased brightness on the visible surface of the
Sun (photosphere) that are associated with strong magnetic fields. They have
been found to be locations associated with solar flares, which occur when
energy stored in sunspot magnetic fields is suddenly released. The processes
involved in flaring and the link between sunspot magnetic fields and flares is
still not fully understood, and this thesis aims to gain a better understanding
of these topics. The magnetic field evolution of a number of sunspot regions is
examined using high spatial resolution data from the Hinode spacecraft. The
research presented in this thesis gives insight into both photospheric and
coronal magnetic field evolution of flaring regions. Significant increases in
vertical field strength, current density, and field inclination angle towards
the vertical are observed in the photosphere just hours before a flare occurs,
which is on much shorter timescales than previously studied. First observations
of spatial changes in field inclination across a magnetic neutral line
(generally believed to be a typical source region of flares) are also
discovered. 3D magnetic field extrapolation methods are used to study the
coronal magnetic field, using the photospheric magnetic field data as a
boundary condition. Magnetic energy and free magnetic energy are observed to
increase significantly a few hours before a flare, and decrease afterwards,
which is a similar trend to the photospheric field parameter changes observed.
Evidence of partial Taylor relaxation is also detected after a flare, as
predicted by several previous studies. The results outlined in this thesis show
that this particular field of research is vital in furthering our understanding
of the magnetic nature of sunspots and its link to flare processes.Comment: PhD Thesis, Trinity College Dublin, Ireland; Supervisors: Dr. D.
Shaun Bloomfield and Dr. Peter T. Gallagher. 255 pages, 81 figures, 12 table
Positive aspects of voice-hearing:a qualitative metasynthesis
Voice-hearing occurs in clinical and non-clinical samples, and the role of spiritual and cultural frameworks of understanding for percipients has received increased attention. This review aimed to identify and synthesise the existing qualitative literature relating to positive aspects of voice-hearing experiences, and to make recommendations based on these findings for clinical practice and future research. Qualitative papers that included positive aspects of voice-hearing were identified by undertaking a systematic search of six electronic databases, resulting in 22 papers. The quality of each paper was assessed and the meta-ethnographic approach was used to extract and synthesise the data. Six themes were identified relating to voices providing safety and protection, guidance, creating psychological and emotional well-being, providing companionship, facilitating personal growth and development, and connecting hearers to religious or spiritual belief systems. The findings suggest positive aspects of voice-hearing that may have clinical and research implications
Analysis of Circuits for Dosage Control in Microbial Populations
Designing genetic circuits to control the behaviors of microbial populations is an ongoing challenge in synthetic biology. Here we analyze circuits which implement dosage control by controlling levels of a global signal in a microbial population in face of varying cell density, growth rate, and environmental dilution. We utilize the Lux quorum sensing system to implement dosage control circuits, and we analyze the dynamics of circuits using both simplified analytical analysis and in silico simulations. We demonstrate that strong negative feedback through inhibiting LuxI synthase expression along with AiiA degradase activity results in circuits with fast response times and robustness to cell density and dilution rate. We find that degradase activity yields robustness to variations in population density for large population sizes, while negative feedback to synthase production decreases sensitivity to dilution rates
Ensemble Forecasting of Major Solar Flares: Methods for Combining Models
One essential component of operational space weather forecasting is the prediction of solar flares. With a multitude of flare forecasting methods now available online it is still unclear which of these methods performs best, and none are substantially better than climatological forecasts. Space weather researchers are increasingly looking towards methods used by the terrestrial weather community to improve current forecasting techniques. Ensemble forecasting has been used in numerical weather prediction for many years as a way to combine different predictions in order to obtain a more accurate result. Here we construct ensemble forecasts for major solar flares by linearly combining the full-disk probabilistic forecasts from a group of operational forecasting methods (ASAP, ASSA, MAG4, MOSWOC, NOAA, and MCSTAT). Forecasts from each method are weighted by a factor that accounts for the method's ability to predict previous events, and several performance metrics (both probabilistic and categorical) are considered. It is found that most ensembles achieve a better skill metric (between 5\% and 15\%) than any of the members alone. Moreover, over 90\% of ensembles perform better (as measured by forecast attributes) than a simple equal-weights average. Finally, ensemble uncertainties are highly dependent on the internal metric being optimized and they are estimated to be less than 20\% for probabilities greater than 0.2. This simple multi-model, linear ensemble technique can provide operational space weather centres with the basis for constructing a versatile ensemble forecasting system -- an improved starting point to their forecasts that can be tailored to different end-user needs
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