26 research outputs found
3D Coronal Density Reconstruction and Retrieving the Magnetic Field Structure during Solar Minimum
Measurement of the coronal magnetic field is a crucial ingredient in
understanding the nature of solar coronal phenomena at all scales. We employed
STEREO/COR1 data obtained during a deep minimum of solar activity in February
2008 (Carrington rotation CR 2066) to retrieve and analyze the
three-dimensional (3D) coronal electron density in the range of heights from
1.5 to 4 Rsun using a tomography method. With this, we qualitatively deduced
structures of the coronal magnetic field. The 3D electron density analysis is
complemented by the 3D STEREO/EUVI emissivity in the 195 A band obtained by
tomography for the same CR. A global 3D MHD model of the solar corona was used
to relate the reconstructed 3D density and emissivity to open/closed magnetic
field structures. We show that the density maximum locations can serve as an
indicator of current sheet position, while the locations of the density
gradient maximum can be a reliable indicator of coronal hole boundaries. We
find that the magnetic field configuration during CR 2066 has a tendency to
become radially open at heliocentric distances greater than 2.5 Rsun. We also
find that the potential field model with a fixed source surface (PFSS) is
inconsistent with the boundaries between the regions with open and closed
magnetic field structures. This indicates that the assumption of the potential
nature of the coronal global magnetic field is not satisfied even during the
deep solar minimum. Results of our 3D density reconstruction will help to
constrain solar coronal field models and test the accuracy of the magnetic
field approximations for coronal modeling.Comment: Published in "Solar Physics
Outbreak of Middle East Respiratory Syndrome at Tertiary Care Hospital, Jeddah, Saudi Arabia, 2014
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
The Helioseismic and Magnetic Imager (HMI) Investigation for the Solar Dynamics Observatory (SDO)
Association of the CHEK2 c.1100delC variant, radiotherapy, and systemic treatment with contralateral breast cancer risk and breast cancer-specific survival
Background
Breast cancer (BC) patients with a germline CHEK2 c.1100delC variant have an increased risk of contralateral BC (CBC) and worse BC-specific survival (BCSS) compared to non-carriers.
Aim
To assessed the associations of CHEK2 c.1100delC, radiotherapy, and systemic treatment with CBC risk and BCSS.
Methods
Analyses were based on 82,701 women diagnosed with a first primary invasive BC including 963 CHEK2 c.1100delC carriers; median follow-up was 9.1 years. Differential associations with treatment by CHEK2 c.1100delC status were tested by including interaction terms in a multivariable Cox regression model. A multi-state model was used for further insight into the relation between CHEK2 c.1100delC status, treatment, CBC risk and death.
Results
There was no evidence for differential associations of therapy with CBC risk by CHEK2 c.1100delC status. The strongest association with reduced CBC risk was observed for the combination of chemotherapy and endocrine therapy [HR (95% CI): 0.66 (0.55–0.78)]. No association was observed with radiotherapy. Results from the multi-state model showed shorter BCSS for CHEK2 c.1100delC carriers versus non-carriers also after accounting for CBC occurrence [HR (95% CI): 1.30 (1.09–1.56)].
Conclusion
Systemic therapy was associated with reduced CBC risk irrespective of CHEK2 c.1100delC status. Moreover, CHEK2 c.1100delC carriers had shorter BCSS, which appears not to be fully explained by their CBC risk
A genome-wide gene-environment interaction study of breast cancer risk for women of European ancestry
Background
Genome-wide studies of gene–environment interactions (G×E) may identify variants associated with disease risk in conjunction with lifestyle/environmental exposures. We conducted a genome-wide G×E analysis of ~ 7.6 million common variants and seven lifestyle/environmental risk factors for breast cancer risk overall and for estrogen receptor positive (ER +) breast cancer.
Methods
Analyses were conducted using 72,285 breast cancer cases and 80,354 controls of European ancestry from the Breast Cancer Association Consortium. Gene–environment interactions were evaluated using standard unconditional logistic regression models and likelihood ratio tests for breast cancer risk overall and for ER + breast cancer. Bayesian False Discovery Probability was employed to assess the noteworthiness of each SNP-risk factor pairs.
Results
Assuming a 1 × 10–5 prior probability of a true association for each SNP-risk factor pairs and a Bayesian False Discovery Probability < 15%, we identified two independent SNP-risk factor pairs: rs80018847(9p13)-LINGO2 and adult height in association with overall breast cancer risk (ORint = 0.94, 95% CI 0.92–0.96), and rs4770552(13q12)-SPATA13 and age at menarche for ER + breast cancer risk (ORint = 0.91, 95% CI 0.88–0.94).
Conclusions
Overall, the contribution of G×E interactions to the heritability of breast cancer is very small. At the population level, multiplicative G×E interactions do not make an important contribution to risk prediction in breast cancer
Magnetohydrodynamic Oscillations in the Solar Corona and Earth’s Magnetosphere: Towards Consolidated Understanding
Quantifying short-term surface changes on recreational trails: The use of topographic surveys and ‘digital elevation models of differences’ (DODs)
This study applied a new method for detailed surveys of short-term dynamics in the surface of recreational trails. The main objectives of this study were: (1) to analyze the spatial aspect of surface changes in microscale; (2) to quantify precisely the short-term rate of soil loss and deposition. Measurements were taken in 12 test fields, located in two protected natural areas in the south of Poland: the Gorce National Park and Poprad Landscape Park. The measuring places were located on trails characterized by different slopes, types of vegetation, and types of use. Each of the test fields was established by four special marks, firmly dug into the ground. The use of precise elevation data provided by the electronic total station and digital elevation models (DEMs) of difference allowed us to assess the sediment budget of the surface changes. The proposed method allowed for obtaining information not only for profile lines but also for specified areas. In such a way, the spatial and temporal dynamics of geomorphologic processes influencing the trail tread could be studied. During a two-year period (2008–2010), soil loss dominated within 10 test fields, while a predominance of deposition was recorded for the remaining two. The average net volumetric change of the trail surface varied from − 0.035 m3 m− 2 per year to + 0.005 m3 m− 2 per year. The short-term dynamics was high and several test fields had a positive balance (predominance of deposition) in one period and negative balance (predominance of soil loss) in the next period. Local geomorphic conditions, morphology of the trail tread and soil properties seemed to be the most important factors contributing to the relief transformation. No connection was demonstrated between the amount of use (i.e. number of visitors) or type of use and the amount of soil loss or deposition