Dear All,
I am Abhishek Rajhans, a graduate student at IUCAA, working under supervision of Durgesh Tripathi (IUCAA) and Vinay Kashyap (CfA). We recently got our paper "Hydrodynamics of small transient brightenings in Solar Corona" accepted in the Astrophysical Journal. In this work we have used EBTEL code, which is based on 0-D description of coronal loops, to study transient brightenings detected by Hi-C and studied using AIA by Subramanian et al 2018. We see that these brightenings can be …
[View More]modelled as loops of ~ 1 Mm, with energy deposition of log[E(ergs)] ~ 23 in ~ 50 seconds. We have used two approaches : [1] in which the background + transient is used for constraining input parameters for simulations and [2] in which only transient has been used. We see that the latter method works better, in terms of agreement of synthetic and observed intensities in the six AIA filters (9.4, 13.1, 17.1, 19.3, 21.1, and 33.5 nm).
It is well known that impulsive events like large flares, microflares and nanoflares, show an initial conduction dominated cooling phase followed by enthalpy flux into corona, and subsequent radiation. Their hydrodynamics can be explained well by physics that goes into EBTEL. The fact that these small transient brightenings can also be explained by same physics is suggestive of a common underlying mechanism.
Here is the arxiv link of the paper
https://arxiv.org/abs/2105.08800
I hope you enjoy reading it. I would be delighted to get your valuable feedbacks, comments, questions and suggestions.
Regards,
Abhishek Rajhans
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Hi Jim
Thanks for sharing this nice paper. The ideas you develop do seem very consistent with some of my earlier work, and indeed you do reference Hood et al (2009) (doi: 10.1051/0004-6361/200912285) - thank you! We showed here that even very smooth and simple motions in the photosphere can produce a very complex field in the corona with multiple fragmented current sheets. Whether one calls this "turbulence" or not is a matter of nomenclature, but it is certainly not classic Kolmogorov. Your …
[View More]statement "It nonetheless has a complex structure that bears no direct relationship to the pattern of driving" sums this up very nicely.
Prior to this, Browning and Van der Linden (2003) (doi 10.1051/0004-6361:20021887) proposed that a repeated series of energy release triggered by kink instability could produce a distribution of nanoflares - this was verified by Bareford et al (2010, 2011) (10.1051/0004-6361/201014067) where we show you can actually get a power law distribution from a random twistings. These were simple semi-analytical models, but I think there is scope to follow through on some of these ideas with simulations.
Of course the reality involves ongoing and more complex patterns of driving- and the possibility of avalanching, as we showed in Hood et al (2016) (10.3847/0004-637X/817/1/5) and pursued in the interesting recent work of Knizhnik et al of course. It seems one localised kink instability can generate a lot of current sheets and energy release!
Best wishes
Philippa
-----Original Message-----
From: Loops <loops-bounces(a)solar.physics.montana.edu> On Behalf Of loops-request(a)solar.physics.montana.edu
Sent: 18 May 2021 19:00
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Today's Topics:
1. Is the corona turbulent? (Klimchuk, James A. (GSFC-6710))
----------------------------------------------------------------------
Message: 1
Date: Tue, 18 May 2021 13:24:09 +0000
From: "Klimchuk, James A. (GSFC-6710)" <james.a.klimchuk(a)nasa.gov>
To: " (Loops(a)solar.physics.montana.edu)"
<Loops(a)solar.physics.montana.edu>
Subject: [Loops] Is the corona turbulent?
Message-ID:
<BY3PR09MB857890CB88D737802F4BB975B02C9(a)BY3PR09MB8578.namprd09.prod.outlook.com>
Content-Type: text/plain; charset="us-ascii"
Dear "loops" friends,
You might be interested in the paper that Spiro and I just published concerning the role of turbulence in forming the current sheets that spawn nanoflares in the magnetically closed corona:
http://journal.frontiersin.org/article/10.3389/fspas.2021.662861/full?&utm_…<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Flinks.emai…
g6QSXzWA2wXgA4DkQrYG8zw9-2BrhOoZY5D8wkA-3D-3D&data=04%7C01%7Cjames.a.klimchuk%40nasa.gov%7C5e1b386e3d2042eee27f08d919b402e2%7C7005d45845be48ae8140d43da96dd17b%7C0%7C0%7C637569083199946822%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=hjrQ5rwifhz4O8XDZt6jIUTLTdxEi45UOl%2FQuFGWNOU%3D&reserved=0>
We argue that the sheets form primarily from other processes, unrelated to turbulence. Localized temporary bursts of turbulence may nonetheless be generated when the sheets reconnect.
Abstract:
We argue that the magnetically closed corona evolves primarily quasi-statically, punctuated by many localized bursts of activity associated with magnetic reconnection at a myriad of small current sheets. The sheets form by various processes that do not involve a traditional turbulent cascade whereby energy flows losslessly through a continuum of spatial scales starting from the large scale of the photospheric driving. If such an inertial range is a defining characteristic of turbulence, then the magnetically closed corona is not a turbulent system. It nonetheless has a complex structure that bears no direct relationship to the pattern of driving.
Cheers,
Jim
********************************************************************************
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<tel:%28301%29%20286-9060>
Fax: 1-301-286-7194<tel:%28301%29%20286-7194>
E-mail: James.A.Klimchuk(a)nasa.gov<mailto:James.A.Klimchuk@nasa.gov>
Homepage: http://science.gsfc.nasa.gov/sed/bio/james.a.klimchuk<http://science.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iPhon…>
No endorsement by NASA is implied for any correspondence related to my official role in professional organizations.
********************************************************************************
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Dear "loops" friends,
You might be interested in the paper that Spiro and I just published concerning the role of turbulence in forming the current sheets that spawn nanoflares in the magnetically closed corona:
http://journal.frontiersin.org/article/10.3389/fspas.2021.662861/full?&utm_…<https://gcc02.safelinks.protection.outlook.com/?url=http%3A%2F%2Flinks.emai…>
We argue that the sheets form primarily from other processes, unrelated to turbulence. Localized temporary bursts of …
[View More]turbulence may nonetheless be generated when the sheets reconnect.
Abstract:
We argue that the magnetically closed corona evolves primarily quasi-statically, punctuated by many localized bursts of activity associated with magnetic reconnection at a myriad of small current sheets. The sheets form by various processes that do not involve a traditional turbulent cascade whereby energy flows losslessly through a continuum of spatial scales starting from the large scale of the photospheric driving. If such an inertial range is a defining characteristic of turbulence, then the magnetically closed corona is not a turbulent system. It nonetheless has a complex structure that bears no direct relationship to the pattern of driving.
Cheers,
Jim
********************************************************************************
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<tel:%28301%29%20286-9060>
Fax: 1-301-286-7194<tel:%28301%29%20286-7194>
E-mail: James.A.Klimchuk(a)nasa.gov<mailto:James.A.Klimchuk@nasa.gov>
Homepage: http://science.gsfc.nasa.gov/sed/bio/james.a.klimchuk<http://science.gsfc.nasa.gov/sed/index.cfm?fuseAction=people.jumpBio&&iPhon…>
No endorsement by NASA is implied for any correspondence related to my official role in professional organizations.
********************************************************************************
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Dear all,
Hope this mail finds you all in good health and spirits. I am Vishal
Upendran, graduate student working with Prof. Durgesh Tripathi at IUCAA,
Pune, India on coronal heating and solar wind emergence.
Our work on the impulsive heating of Quiet Corona was recently accepted for
publication in ApJ. Essentially, we study pixel-wise light curves of Quiet
Sun regions in the 171 Å, 193 Å and 211 Å from AIA by combining the
empirical, statistical impulsive heating forward model of Pauluhn &…
[View More]amp; Solanki
(2007) with a machine-learning inversion model that allows uncertainty
quantification.
On performing inversions across approx. 300,000 light curves, we find that
there are approximately 2--3 impulsive events per min, with a lifetime of
about 10--20 min. The power law slope distribution peaks above 2 for all
passbands. We then explore correlations among the frequency of impulsive
events, their timescales and peak energy. The correlations suggest that
conduction losses dominate over radiative cooling losses, and there might
be a reservoir of energy either depleted by frequent, small events or
infrequent, large events.
I am excited to obtain feedback from the community on this work, and hope
it would be an enjoyable read to you.
The arxiv link: https://arxiv.org/abs/2103.16824.
Best regards,
Vishal
--
Vishal Upendran,
Senior Research Fellow, Inter-University Centre for Astronomy and
Astrophysics (IUCAA),
Pune, India - 411007
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