614 research outputs found
Spectroscopic Observations and Modelling of Impulsive Alfv\'en Waves Along a Polar Coronal Jet
Using the Hinode/EIS 2 spectroscopic observations, we study the intensity,
velocity, and FWHM variations of the strongest Fe XII 195.12 \AA\ line along
the jet to find the signature of Alfv\'en waves. We simulate numerically the
impulsively generated Alfv\'en waves within the vertical Harris current-sheet,
forming the jet plasma flows, and mimicking their observational signatures.
Using the FLASH code and the atmospheric model with embedded weakly expanding
magnetic field configuration within a vertical Harris current-sheet, we solve
the two and half-dimensional (2.5-D) ideal magnetohydrodynamic (MHD) equations
to study the evolution of Alfv\'en waves and vertical flows forming the plasma
jet. At a height of from the base of the jet, the
red-shifted velocity component of Fe XII 195.12 \AA\ line attains its maximum
() which converts into a blue-shifted one between the
altitude of . The spectral intensity continously increases up
to , while FWHM still exhibits the low values with almost
constant trend. This indicates that the reconnection point within the jet's
magnetic field topology lies in the corona from its
footpoint anchored in the Sun's surface. Beyond this height, FWHM shows a
growing trend. This may be the signature of Alfv\'en waves that impulsively
evolve due to reconnection and propagate along the jet. From our numerical
data, we evaluate space- and time- averaged Alfv\'en waves velocity amplitudes
at different heights in the jet's current-sheet, which contribute to the
non-thermal motions and spectral line broadening. The synthetic width of Fe XII
line exhibits similar trend of increment as in the
observational data, possibly proving the existence of impulsively generated (by
reconnection) Alfv\'en waves which propagate along the jet
On Thermal-Pulse-Driven Plasma Flows in Coronal Funnels as Observed by Hinode/EUV Imaging Spectrometer (EIS)
Using one-arcsecond-slit scan observations from the Hinode/EUV Imaging
Spectrometer (EIS) on 05 February 2007, we find the plasma outflows in the open
and expanding coronal funnels at the eastern boundary of AR 10940. The Doppler
velocity map of Fe XII 195.120 A shows that the diffuse close-loop system to be
mostly red-shifted. The open arches (funnels) at the eastern boundary of AR
exhibit blue-shifts with a maximum speed of about 10-15 km/s. This implies
outflowing plasma through these magnetic structures. In support of these
observations, we perform a 2D numerical simulation of the expanding coronal
funnels by solving the set of ideal MHD equations in appropriate VAL-III C
initial temperature conditions using the FLASH code. We implement a rarefied
and hotter region at the footpoint of the model funnel, which results in the
evolution of slow plasma perturbations propagating outward in the form of
plasma flows. We conclude that the heating, which may result from magnetic
reconnection, can trigger the observed plasma outflows in such coronal funnels.
This can transport mass into the higher corona, giving rise to the formation of
the nascent solar wind.Comment: 17 Pages; 7 Figure
3D numerical simulations of propagating two-fluid, torsional Alfv\'en waves and heating of a partially-ionized solar chromosphere
We present a new insight into the propagation, attenuation and dissipation of
two-fluid, torsional Alfv\'en waves in the context of heating of the lower
solar atmosphere. By means of numerical simulations of the partially-ionized
plasma, we solve the set of two-fluid equations for ion plus electron and
neutral fluids in three-dimensional (3D) Cartesian geometry. We implement
initially a current-free magnetic field configuration, corresponding to a
magnetic flux-tube that is rooted in the solar photosphere and expands into the
chromosphere and corona. We put the lower boundary of our simulation region in
the low chromosphere, where ions and neutrals begin to decouple, and implement
there a monochromatic driver that directly generates Alfv\'en waves with a wave
period of 30 s. As the ion-neutral drift increases with height, the two-fluid
effects become more significant and the energy carried by both Alfv\'en and
magneto-acoustic waves can be thermalized in the process of ion-neutral
collisions there. In fact, we observe a significant increase in plasma
temperature along the magnetic flux-tube. In conclusion, the two-fluid
torsional Alfv\'en waves can potentially play a role in the heating of the
solar chromosphere.Comment: 10 pages, 7 figure
Rotating Network Jets in the quiet Sun as Observed by IRIS
Aims. We perform a detailed observational analysis of network jets to
understand their kinematics, rotational motion and underlying triggering
mechanism(s). We have analyzed the quiet-Sun (QS) data. Methods. IRIS high
resolution imaging and spectral observations (SJI: Si iv 1400.0 \AA, Raster: Si
iv 1393.75 \AA) are used to analyze the omnipresent rotating network jets in
the transition-region (TR). In addition, we have also used Atmospheric Imaging
Assembly (AIA) onboard Solar Dynamic Observation (SDO) observations. Results.
The statistical analysis of fifty-one network jets is performed to understand
various their mean properties, e.g., apparent speed (140.16+/-39.41 km/s),
length (3.16+/-1.18 Mm), lifetimes (105.49+/-51.75 s). The Si iv 1393.75 \AA
line has secondary component along with its main Gaussian, which is formed due
to the high-speed plasma flows (i.e., network jets). The variation of Doppler
velocity across these jets (i.e., blue shift on one edge and red shift on the
other) signify the presence of inherited rotational motion. The statistical
analysis predicts that the mean rotational velocity (i.e., \delV) is 49.56
km/s. The network jets have high angular velocity in comparison to the other
class of solar jets. Conclusions. The signature of network jets are inherited
in TR spectral lines in terms of the secondary component of the Si iv 1393.75
\AA line. The rotational motion of network jets is omnipresent, which is
reported firstly for this class of jet-like features. The magnetic reconnection
seems to be the most favorable mechanism for the formation of these network
jets.Comment: 14 Pages; 6 Figures; In Press Astronomy & Astrophysic
Spillover from marine reserves and the replenishment of fished stocks
Author Posting. © Foundation for Environmental Conservation, 2009. This article is posted here by permission of Cambridge University Press for personal use, not for redistribution. The definitive version was published in Environmental Conservation 36 (2009): 268-276, doi:10.1017/S0376892910000032.No-take marine reserves are widely recognized as an effective conservation tool for protecting marine resources. Despite considerable empirical evidence that abundance and biomass of fished species increase within marine reserve boundaries, the potential for reserves to provide fisheries and conservation benefits to adjacent waters remains heavily debated. This paper uses statistical and population models to evaluate published empirical data on adult spillover from marine reserves and shows that spillover is a common phenomenon for species that respond positively to reserve protection, but at relatively small scales, detectable on average up to 800 m from reserve boundaries. At these small scales, local fisheries around reserves were likely unsustainable in 12 of 14 cases without the reserve, and spillover partially or fully offsets losses in catch due to reserve closure in the other two cases. For reserves to play a role in sustaining and replenishing larger-scale fished stocks, networks of reserves may be necessary, but as few exist this is difficult to evaluate. The results suggest reserves can simultaneously meet conservation objectives and benefit local fisheries adjacent to their boundaries.Support was provided by
a grant from the David and Lucille Packard Foundation to
NCEAS for ecosystem-based management ofmarine systems,
the Partnership for Interdisciplinary Studies of Coastal
Oceans (PISCO) funded by the David and Lucile Packard
Foundation and the Gordon and Betty Moore Foundation
(contribution number 348), the Sustainable Fisheries Group
supported by the Paul G. Allen Family Foundation and
the Bahamas Biocomplexity Project (US NSF Biocomplexity
grantOCE-0119976) andUS EPA Science to Achieve Results
(R832223)
Density of States and Conductivity of Granular Metal or Array of Quantum Dots
The conductivity of a granular metal or an array of quantum dots usually has
the temperature dependence associated with variable range hopping within the
soft Coulomb gap of density of states. This is difficult to explain because
neutral dots have a hard charging gap at the Fermi level. We show that
uncontrolled or intentional doping of the insulator around dots by donors leads
to random charging of dots and finite bare density of states at the Fermi
level. Then Coulomb interactions between electrons of distant dots results in
the a soft Coulomb gap. We show that in a sparse array of dots the bare density
of states oscillates as a function of concentration of donors and causes
periodic changes in the temperature dependence of conductivity. In a dense
array of dots the bare density of states is totally smeared if there are
several donors per dot in the insulator.Comment: 13 pages, 15 figures. Some misprints are fixed. Some figures are
dropped. Some small changes are given to improve the organizatio
Resonantly damped surface and body MHD waves in a solar coronal slab with oblique propagation
The theory of magnetohydrodynamic (MHD) waves in solar coronal slabs in a
zero- configuration and for parallel propagation of waves does not allow
the existence of surface waves. When oblique propagation of perturbations is
considered both surface and body waves are able to propagate. When the
perpendicular wave number is larger than a certain value, the body kink mode
becomes a surface wave. In addition, a sausage surface mode is found below the
internal cut-off frequency. When non-uniformity in the equilibrium is included,
surface and body modes are damped due to resonant absorption. In this paper,
first, a normal-mode analysis is performed and the period, the damping rate,
and the spatial structure of eigenfunctions are obtained. Then, the
time-dependent problem is solved, and the conditions under which one or the
other type of mode is excited are investigated.Comment: 19 pages, 9 figures, accepted for publication in Solar Physic
Multiwavelength Observations of Supersonic Plasma Blob Triggered by Reconnection Generated Velocity Pulse in AR10808
Using multi-wavelength observations of Solar and Heliospheric Observatory
(SoHO)/Michelson Doppler Imager (MDI), Transition Region and Coronal Explorer
(TRACE) 171 \AA, and H from Culgoora Solar Observatory at Narrabri,
Australia, we present a unique observational signature of a propagating
supersonic plasma blob before an M6.2 class solar flare in AR10808 on 9th
September 2005. The blob was observed between 05:27 UT to 05:32 UT with almost
a constant shape for the first 2-3 minutes, and thereafter it quickly vanished
in the corona. The observed lower bound speed of the blob is estimated as
215 km s in its dynamical phase. The evidence of the blob with
almost similar shape and velocity concurrent in H and TRACE 171 \AA\
supports its formation by multi-temperature plasma. The energy release by a
recurrent 3-D reconnection process via the separator dome below the magnetic
null point, between the emerging flux and pre-existing field lines in the lower
solar atmosphere, is found to be the driver of a radial velocity pulse outwards
that accelerates this plasma blob in the solar atmosphere. In support of
identification of the possible driver of the observed eruption, we solve the
two-dimensional ideal magnetohydrodynamic equations numerically to simulate the
observed supersonic plasma blob. The numerical modelling closely match the
observed velocity, evolution of multi-temperature plasma, and quick vanishing
of the blob found in the observations. Under typical coronal conditions, such
blobs may also carry an energy flux of 7.0 ergs cm
s to re-balance the coronal losses above active regions.Comment: Solar Physics; 22 Pages; 8 Figure
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