1,782 research outputs found
Seismic Constraints on Interior Solar Convection
We constrain the velocity spectral distribution of global-scale solar
convective cells at depth using techniques of local helioseismology. We
calibrate the sensitivity of helioseismic waves to large-scale convective cells
in the interior by analyzing simulations of waves propagating through a
velocity snapshot of global solar convection via methods of time-distance
helioseismology. Applying identical analysis techniques to observations of the
Sun, we are able to bound from above the magnitudes of solar convective cells
as a function of spatial convective scale. We find that convection at a depth
of with spatial extent , where is the
spherical harmonic degree, comprise weak flow systems, on the order of 15 m/s
or less. Convective features deeper than are more difficult
to image due to the rapidly decreasing sensitivity of helioseismic waves.Comment: accepted, ApJ Letters, 5 figures, 10 pages (in this version
Using Coronal Loops to Reconstruct the Magnetic Field of an Active Region Before and After a Major Flare
The shapes of solar coronal loops are sensitive to the presence of electrical
currents that are the carriers of the nonpotential energy available for
impulsive activity. We use this information in a new method for modeling the
coronal magnetic field of AR 11158 as a nonlinear force-free field (NLFFF). The
observations used are coronal images around time of major flare activity on
2011/02/15, together with the surface line-of-sight magnetic field
measurements. The data are from the Helioseismic and Magnetic Imager and
Atmospheric Imaging Assembly (HMI and AIA, respectively) onboard the Solar
Dynamics Observatory (SDO). The model fields are constrained to approximate the
coronal loop configurations as closely as possible, while also subject to the
force-free constraints. The method does not use transverse photospheric
magnetic field components as input, and is thereby distinct from methods for
modeling NLFFFs based on photospheric vector magnetograms. We validate the
method using observations of AR 11158 at a time well before major flaring, and
subsequently review the field evolution just prior to and following an X2.2
flare and associated eruption. The models indicate that the energy released
during the instability is about erg, consistent with what is
needed to power such a large eruptive flare. Immediately prior to the eruption
the model field contains a compact sigmoid bundle of twisted flux that is not
present in the post-eruption models, which is consistent with the observations.
The core of that model structure is twisted by full turns about
its axis.Comment: ApJ, in pres
Structure and Evolution of Giant Cells in Global Models of Solar Convection
The global scales of solar convection are studied through three-dimensional
simulations of compressible convection carried out in spherical shells of
rotating fluid which extend from the base of the convection zone to within 15
Mm of the photosphere. Such modelling at the highest spatial resolution to date
allows study of distinctly turbulent convection, revealing that coherent
downflow structures associated with giant cells continue to play a significant
role in maintaining the strong differential rotation that is achieved. These
giant cells at lower latitudes exhibit prograde propagation relative to the
mean zonal flow, or differential rotation, that they establish, and retrograde
propagation of more isotropic structures with vortical character at mid and
high latitudes. The interstices of the downflow networks often possess strong
and compact cyclonic flows. The evolving giant-cell downflow systems can be
partly masked by the intense smaller scales of convection driven closer to the
surface, yet they are likely to be detectable with the helioseismic probing
that is now becoming available. Indeed, the meandering streams and varying
cellular subsurface flows revealed by helioseismology must be sampling
contributions from the giant cells, yet it is difficult to separate out these
signals from those attributed to the faster horizontal flows of
supergranulation. To aid in such detection, we use our simulations to describe
how the properties of giant cells may be expected to vary with depth, how their
patterns evolve in time, and analyze the statistical features of correlations
within these complex flow fields.Comment: 22 pages, 16 figures (color figures are low res), uses emulateapj.cls
Latex class file, Results shown during a Press release at the AAS meeting in
June 2007. Submitted to Ap
Modeling Magnetic Field Structure of a Solar Active Region Corona using Nonlinear Force-Free Fields in Spherical Geometry
We test a nonlinear force-free field (NLFFF) optimization code in spherical
geometry using an analytical solution from Low and Lou. Several tests are run,
ranging from idealized cases where exact vector field data are provided on all
boundaries, to cases where noisy vector data are provided on only the lower
boundary (approximating the solar problem). Analytical tests also show that the
NLFFF code in the spherical geometry performs better than that in the Cartesian
one when the field of view of the bottom boundary is large, say, . Additionally, We apply the NLFFF model to an active region
observed by the Helioseismic and Magnetic Imager (HMI) on board the Solar
Dynamics Observatory (SDO) both before and after an M8.7 flare. For each
observation time, we initialize the models using potential field source surface
(PFSS) extrapolations based on either a synoptic chart or a flux-dispersal
model, and compare the resulting NLFFF models. The results show that NLFFF
extrapolations using the flux-dispersal model as the boundary condition have
slightly lower, therefore better, force-free and divergence-free metrics, and
contain larger free magnetic energy. By comparing the extrapolated magnetic
field lines with the extreme ultraviolet (EUV) observations by the Atmospheric
Imaging Assembly (AIA) on board SDO, we find that the NLFFF performs better
than the PFSS not only for the core field of the flare productive region, but
also for large EUV loops higher than 50 Mm.Comment: 34 pages, 8 figures, accepted for publication in Ap
Perceived parenting syle and social problem solving skills in young adults
The present study examined whether the type of parenting style as perceived by young adults is associated with social problem solving skills using a performance based task. Thirty-nine participants between the ages of 19 and 24 were given a Parental Authority Questionnaire (PAQ) and a performance-based Social Problem Solving Skills task (SPST). It was hypothesized that higher ratings on the authoritative style parenting scale would be correlated with more effective solutions for social problems and fewer self-critical and hostile attributions. Results showed a significant relationship between non authoritative parenting, specifically permissive, and content of chosen response, r(39) = -.36, p\u3c .05, which supported the hypothesis. However, there was an interesting opposition to the hypothesis regarding self-critical attributions, where Authoritative parenting significantly correlated with more self-critical attributions, r(39) = .35, p\u3c .05
Coronal radiation belts
The magnetic field of the solar corona has a large-scale dipole character,
which maps into the bipolar field in the solar wind. Using standard
representations of the coronal field, we show that high-energy ions can be
trapped stably in these large-scale closed fields. The drift shells that
describe the conservation of the third adiabatic invariant may have complicated
geometries. Particles trapped in these zones would resemble the Van Allen Belts
and could have detectable consequences. We discuss potential sources of trapped
particles
Solar Multi-Scale Convection and Rotation Gradients Studied in Shallow Spherical Shells
The differential rotation of the sun, as deduced from helioseismology,
exhibits a prominent radial shear layer near the top of the convection zone
wherein negative radial gradients of angular velocity are evident in the low-
and mid-latitude regions spanning the outer 5% of the solar radius.
Supergranulation and related scales of turbulent convection are likely to play
a significant role in the maintenance of such radial gradients, and may
influence dynamics on a global scale in ways that are not yet understood. To
investigate such dynamics, we have constructed a series of three-dimensional
numerical simulations of turbulent compressible convection within spherical
shells, dealing with shallow domains to make such modeling computationally
tractable. These simulations are the first models of solar convection in a
spherical geometry that can explicitly resolve both the largest dynamical
scales of the system (of order the solar radius) as well as smaller-scale
convective overturning motions comparable in size to solar supergranulation
(20--40 Mm). We find that convection within these simulations spans a large
range of horizontal scales, and that the radial angular velocity gradient in
these models is typically negative, especially in low- and mid-latitude
regions. Analyses of the angular momentum transport indicates that such
gradients are maintained by Reynolds stresses associated with the convection,
transporting angular momentum inward to balance the outward transport achieved
by viscous diffusion and large-scale flows in the meridional plane. We suggest
that similar mechanisms associated with smaller-scale convection in the sun may
contribute to the maintenance of the observed radial shear layer located
immediately below the solar photosphere.Comment: 45 pages, 17 figures, ApJ in press. A preprint of paper with hi-res
figures can be found at
http://www-lcd.colorado.edu/~derosa/modelling/modelling.htm
A model for standardizing manipulation terminology in physical therapy practice
Research supporting the efficacy of manual therapy, manipulation in particular, is growing. The ability to communicate clearly and accurately regarding this important intervention, regardless of region or background, is essential if clinicians are to incorporate this research in clinical practice. In February 2007, the American Academy of Orthopaedic Manual Physical Therapists formed a task force to standardize manual therapy terminology, starting with the intervention of manipulation. The ultimate goal of this task force was to create a template that has the potential to be used internationally by the community of physical therapists in order to standardize manual therapy nomenclature. The following document reflects the work and recommendations of this task force
- …