Dear all,
the following paper has recently been accepted by ApJ Letters. You can
find a copy of the paper and relevant movies at
www.lmsal.com/~ptesta/hic_moss/
thanks,
Paola
title:
Observing coronal nanoflares in active region moss
authors:
P. Testa, B. De Pontieu, J. Martinez-Sykora, E. DeLuca, V. Hansteen, J.
Cirtain, A. Winebarger, L. Golub, K. Kobayashi, K. Korreck, S. Kuzin, R.
Walsh, C. DeForest, A. Title, M.Weber
abstract:
The High-resolution Coronal Imager (Hi-C) has provided Fe XII 193A
images of the upper transition region moss at an unprecedented spatial
(~0.3-0.4 arcsec) and temporal (5.5s) resolution.
The Hi-C observations show in some moss regions variability on
timescales down to ~15s, significantly shorter than the minute scale
variability typically found in previous observations of moss, therefore
challenging the conclusion of moss being heated in a mostly steady
manner. These rapid variability moss regions are located at the
footpoints of bright hot coronal loops observed by SDO/AIA in the 94A
channel, and by Hinode/XRT.
The configuration of these loops is highly dynamic, and suggestive of
slipping reconnection.
We interpret these events as signatures of heating events associated
with reconnection occurring in the overlying hot coronal loops, i.e.,
coronal nanoflares.
We estimate the order of magnitude of the energy in these events to be
of at least a few $10^{23}$~erg, also supporting the nanoflare scenario.
These Hi-C observations suggest that future observations at comparable
high spatial and temporal resolution, with more extensive temperature
coverage are required to determine the exact characteristics of the
heating mechanism(s).
Hello everyone,
Here are two new papers by Peter Cargill and me that may be of interest to
you.
The first "The influence of numerical resolution on coronal density in
hydrodynamic models of impulsive heating" takes what we believe to be a
long-overdue look at the issues surrounding the question of grid resolution
in numerical models and some of the physical implications of under-resolving
particular regions of the solar atmosphere. The paper has already been
published by ApJ and can be obtained here:
http://iopscience.iop.org/0004-637X/770/1/12/pdf/0004-637X_770_1_12.pdf
The second "The Cooling of Coronal Plasmas. iv: Catastrophic Cooling of
Loops" is a continuation of our series on the relevant cooling processes in
the solar atmosphere. Here we provide a physical explanation of the onset of
catastrophic cooling, which may provide an explanation for the relatively
weak active region emission detected in wavelength channels sensitive to
lower temperature lines. The manuscript has been accepted for publication by
ApJ and is available on astro-ph:
http://arxiv.org/ftp/arxiv/papers/1305/1305.5484.pdf
Hope to see many of you in Montana!
Best,
Steve
Dr Stephen J. Bradshaw
(Assistant Professor of Physics and Astronomy)
Department of Physics and Astronomy, MS-108,
Rice University,
6100 Main Street,
Houston,
TX 77005,
USA.
Tel: +1 713 348 4045
Email: stephen.bradshaw(a)rice.edu
Dear Loop Group,
We have just published a new AIA loop paper in ApJ:
Atmospheric Imaging Assembly Observations of Coronal Loops: Cross-Field Temperature Distributions
Schmelz, J.T., Jenkins, B.S., Pathak, S. (2013), ApJ, 770, 14
Abstract: We construct revised response functions for the Atmospheric Imaging Assembly (AIA) using the new atomic data, ionization equilibria, and coronal abundances available in CHIANTI 7.1. We then use these response functions in multithermal analysis of coronal loops, which allows us to determine a specific cross-field temperature distribution without ad hoc assumptions. Our method uses data from the six coronal filters and the Monte Carlo solutions available from our differential emission measure (DEM) analysis. The resulting temperature distributions are not consistent with isothermal plasma. Therefore, the observed loops cannot be modeled as single flux tubes and must be composed of a collection of magnetic strands. This result is now supported by observations from the High-resolution Coronal Imager, which show fine-scale braiding of coronal strands that are reconnecting and releasing energy. Multithermal analysis is one of the major scientific goals of AIA, and these results represent an important step toward the successful achievement of that goal. As AIA DEM analysis becomes more straightforward, the solar community will be able to take full advantage of the state-of-the-art spatial, temporal, and temperature resolution of the instrument.
You can download a copy here:
http://stacks.iop.org/0004-637X/770/14
I look forward to seeing some of you at Loops VI!
Regards,
Joan
Dear Loop Enthusiasts,
ApJ has just accepted our paper 'Modeling the Line-of-Sight Integrated Emission in the Corona: Implications for Coronal Heating'.
Here is the abstract:
One of the outstanding problems in all of space science is uncovering how the solar corona is heated to temperatures greater than 1 MK. Though studied for decades, one of the major difficulties in solving this problem has been unraveling the line-of-sight (LOS) effects in the observations. The corona is optically thin, so a single pixel measures counts from an indeterminate number (perhaps tens of thousands) of independently heated flux tubes, all along that pixel's LOS. In this paper we model the emission in individual pixels imaging the active region corona in the Extreme Ultraviolet. If LOS effects are not properly taken into account, erroneous conclusions regarding both coronal heating and coronal dynamics may be reached. We model the corona as a LOS integration of many thousands of completely independently heated flux tubes. We demonstrate that despite the superposition of randomly heated flux tubes, nanoflares leave distinct signatures in light curves observed with multi-wavelength and high time cadence data, such as those data taken with the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory. These signatures are readily detected with the time-lag analysis technique of Viall & Klimchuk (2012). Steady coronal heating leaves a different and equally distinct signature that is also revealed by the technique.
You can download a copy at astro-ph until it is officially published by ApJ:
http://arxiv.org/abs/1304.5439v2
Cheers,
Nicki
**************
Nicholeen Viall
Code 671
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Email: Nicholeen.M.Viall(a)nasa.gov<mailto:Nicholeen.M.Viall@nasa.gov>
Phone: 301-286-4054
Dear all,
this is to inform you that the deadline for the abstract submission
to the Coronal Loops Workshop VI has been extended to May 12.
You can submit the abstract and register via the online form at
http://www.stce.be/coronalloops/
Regards
Susanna