Hi everyone,
In the spirit of a number of recent papers that have been focused on trying
to determine the dominant components of the emission in the wavelength
channels of imaging instruments (AIA, in particular), Jim and I would like
to share with you all a link to a paper on this very topic that was recently
published in the ApJ Supplement Series:
http://iopscience.iop.org/0067-0049/194/2/26/pdf/apjs_194_2_26.pdf
Our aim in carrying out the work described in this paper was to provide a
…
[View More]large amount of quantitative data from our modeling studies that we hope
will be of use in the analysis of observationally gathered data.
Best wishes,
Steve
-----Original Message-----
From: loops-bounces(a)solar.physics.montana.edu
[mailto:loops-bounces@solar.physics.montana.edu] On Behalf Of Paola Testa
Sent: Tuesday, September 20, 2011 10:00 AM
To: A mailing list for scientists involved in the observation and modeling
of solar loop structures
Cc: Juan Martinez Sykora
Subject: [Loops] Forward modeling of emission in SDO/AIA passbands from
dynamic 3D simulations
Hello all,
here is a link to a preprint of a paper, accepted for publication on ApJ,
that is also discussing issues related to the interpretation of AIA
observations:
http://adsabs.harvard.edu/abs/2011arXiv1109.0704M
cheers,
Paola
On 9/9/11 12:03 PM, Giulio Del Zanna wrote:
>
> Dear colleagues,
>
> here is a link to a preprint that discusses various
> (important) issues related to the interpretation of AIA data:
>
> http://solar.physics.montana.edu/cgi-bin/eprint/index.pl?entry=15555
>
> Those of you that were present at the excellent Mallorca meeting might
> recall the issues we raised there. The paper, which follows on from
> O'Dwyer et al., contains more.
>
> I encourage all to follow the example in the Appendix to calculate
> your own AIA responses using CHIANTI. We will soon release v.7, but do
> not expect huge differences.
> We are working to try and improve the atomic data for AIA, more to come.
>
>
> best wishes,
_______________________________________________
Loops mailing list
Loops(a)solar.physics.montana.edu
https://mithra.physics.montana.edu/mailman/listinfo/loops
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Dear Loop Group,
The following paper has just come out in ApJ:
The Cold Shoulder: Emission Measure Distributions of Active Region Cores
By Schmelz, J. T. & Pathak, S.
2012, ApJ, 756, 126
http://adsabs.harvard.edu/abs/2012ApJ...756..126S
Abstract
The coronal heating mechanism for active region core loops is difficult to determine because these loops are often not resolved and cannot be studied individually. Rather, we concentrate on the "inter-moss" areas between loop footpoints. We use …
[View More]observations from the Hinode EUV Imaging Spectrometer and the X-Ray Telescope to calculate the emission measure distributions of eight inter-moss areas in five different active regions. The combined data sets provide both high- and low-temperature constraints and ensure complete coverage in the temperature range appropriate for active regions. For AR 11113, the emission can be modeled with heating events that occur on timescales less than the cooling time. The loops in the core regions appear to be close to equilibrium and are consistent with steady heating. The other regions studied, however, appear to be dominated by nanoflare heating. Our results are consistent with the idea that active region age is an important parameter in determining whether steady or nanoflare heating is primarily responsible for the core emission, that is, older regions are more likely to be dominated by steady heating, while younger regions show more evidence of nanoflares.
Comments welcome.
Regards,
Joan
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Dear all,
our paper on testing the MCMC DEM reconstruction method by using 3D MHD
simulations has just been accepted for publication on ApJ. You can find
a preprint at:
http://folk.uio.no/bdp/papers/3dEMD_ptesta.pdf
(It will also appear soon on astro-ph but in an abridged version due to
the length of the paper and astro-ph restrictions on submission size)
Please find the title and abstract below.
cheers,
Paola
Title: "Investigating the reliability of coronal emission measure …
[View More]distribution
diagnostics using 3D radiative MHD simulations"
Authors: Paola Testa, Bart De Pontieu, Juan Martinez-Sykora,
Viggo Hansteen, Mats Carlsson
Abstract:
Determining the temperature distribution of coronal plasmas can provide
stringent constraints on coronal heating. Current observations with the Extreme
ultraviolet Imaging Spectrograph onboard Hinode and the Atmospheric Imaging
Assembly onboard the Solar Dynamics Observatory provide diagnostics of the
emission measure distribution (EMD) of the coronal plasma.
Here we test the reliability of temperature diagnostics using 3D radiative
MHD simulations. We produce synthetic observables from the models, and apply
the Monte Carlo Markov chain EMD diagnostic. By comparing the derived EMDs with
the ``true'' distributions from the model we assess the limitations of the
diagnostics, as a function of the plasma parameters and of the signal-to-noise
of the data.
We find that EMDs derived from EIS synthetic data reproduce some general
characteristics of the true distributions, but usually show differences from
the true EMDs that are much larger than the estimated uncertainties suggest,
especially when structures with significantly different density overlap along
the line-of-sight. When using AIA synthetic data the derived EMDs reproduce the
true EMDs much less accurately, especially for broad EMDs. The differences
between the two instruments are due to the: (1) smaller number of constraints
provided by AIA data, (2) broad temperature response function of the AIA
channels which provide looser constraints to the temperature distribution.
Our results suggest that EMDs derived from current observatories may often
show significant discrepancies from the true EMDs, rendering their
interpretation fraught with uncertainty. These inherent limitations to the
method should be carefully considered when using these distributions to
constrain coronal heating.
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Dear Loop Enthusiasts,
There is a workshop coming up that will be of interest to many of you Nov 27-Dec 2nd: Solar in Sonoma, Tracing the Connections in Solar Eruptive Events. For those attending AGU, this workshop runs the 5 days before AGU. The abstract and early registration deadline are September 14th, and the workshop information can all be found here http://hessi.ssl.berkeley.edu/petaluma/index.shtml. In particular to this community, Iain and I are leading a working group on possible …
[View More]connections between microflares and nanoflares (see description below), and encourage your participation.
We hope to see many of you there!
Nicki
**************
Nicholeen Viall
Code 671
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Email: Nicholeen.M.Viall(a)nasa.gov<https://mail02.ndc.nasa.gov/owa/UrlBlockedError.aspx>
Phone: 301-286-4054
'Working Group 7: Microflares and Nanoflares
Group Leaders: Iain Hannah, Nicki Viall
Flaring energy release occurs over a vast range of scales in the solar atmosphere. The largest X-Class flares down to microflares (A, B-Class) are exclusively active region phenomena and demonstrate similar characteristics of particle acceleration and plasma heating. One can easily envisage that energetically smaller flares beyond the current observational limits also exist due to smaller scale magnetic reconnection events. Indeed, theories to explain certain observational signatures of heating throughout the corona involve such so-called 'nanoflare' events. The power law frequency distribution of flares suggests that there are common features over all energy scales that could also extend to nanoflares. However, unlike microflares and larger flares, nanoflares are not directly observable with current observations, so the question remains: is it accurate to extrapolate the physical features of large flares down to those of nanoflares? What can we learn from such extrapolations, given that the power law distributions are subject to different bias effects and have unknown cut-offs? In this working group we welcome contributions from both observational and theoretical/numerical studies of microflares and nanoflares as well as possible relationships between them.
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Dear Loopers,
Our paper, 'Evidence for Widespread Cooling in an Active Region Observed with the SDO Atmospheric Imaging Assembly' recently came out in ApJ: http://stacks.iop.org/0004-637X/753/35.
NASA did a really nice press release on it: http://svs.gsfc.nasa.gov/vis/a010000/a011000/a011046/ They made a video visualization of the technique we used, and to be honest, the video does a better job explaining the technique than I am able to do sometimes!
Cheers,
Nicki
**************
…
[View More]Nicholeen Viall
Code 671
NASA/Goddard Space Flight Center
Greenbelt, MD 20771
Email: Nicholeen.M.Viall(a)nasa.gov<https://mail02.ndc.nasa.gov/owa/UrlBlockedError.aspx>
Phone: 301-286-4054
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Dear friends,
You might be interested in my recent paper on "The Role of Type II Spicules in the Upper Solar Atmosphere," which can be downloaded at http://arxiv.org/abs/1207.7048
Cheers,
Jim
ABSTRACT:
We examine the suggestion that most of the hot plasma in the Sun's
corona comes from type II spicule material that is heated as it is
ejected from the chromosphere. This contrasts with the traditional
view that the corona is filled via chromospheric evaporation that
results from …
[View More]coronal heating. We explore the observational
consequences of a hypothetical spicule dominated corona and conclude
from the large discrepancy between predicted and actual observations
that only a small fraction of the hot plasma can be supplied by
spicules (<2% in active regions and <5% in the quiet Sun). The
red-blue asymmetries of EUV spectral lines and the ratio of lower
transition region (LTR; T<0.1 MK) to coronal emission measures
are both predicted to be 2 orders of magnitude larger than observed.
Furthermore, hot spicule material would cool dramatically by
adiabatic expansion as it rises into the corona, so coronal heating
would be required to maintain the high temperatures that are seen at
all altitudes. The necessity of coronal heating is inescapable.
Traditional coronal heating models predict far too little emission
from the LTR, and we suggest that this emission comes primarily from
the bulk of the spicule material that is heated to <0.1 MK and
is visible in He II (304 A) as it falls back to the surface.
********************************************************************************
James A. Klimchuk
NASA Goddard Space Flight Center
Solar Physics Lab, Code 671
Bldg. 21, Rm. 158
Greenbelt, MD 20771
USA
Phone: 1-301-286-9060
Fax: 1-301-286-7194
E-mail: James.A.Klimchuk(a)nasa.gov<mailto:James.A.Klimchuk@nasa.gov>
Homepage: https://sedupdate.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iP…
No endorsement by NASA is implied for any correspondence related to my role as an officer of professional organizations (American Geophysical Union, International Astronomical Union, American Astronomical Society).
********************************************************************************
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