[Loops] new paper on IRIS diagnostics for coronal heating and accelerated particles

[Paola Testa]

Hi Phil,

we have addressed this point in the supplementary material of the paper,
giving several reasons why we think it's highly unlikely, and the
non-thermal electrons are a much more natural explanation.

thanks,
Paola


On 10/30/14, 9:54 PM, Philip Judge wrote:
>
>
> If the sun releases 10^25 erg in 30s in the chromosphere,  as needed 
> by these data, cannot this be just local magnetic heating?  A 
> "chromospheric flare"?
>
> Consider magnetic energy density
>
> E= B^2/ 8pi.
>
> In plage let B be say 300G, then E=3e3.  Then for total energy of 
> 10^25 erg we need  3e21 cm3 and d^3=V gives length  d of 10^7 cm, or 
> 0.1 Mm.  If I use rho= 1e-10 g for mid chromosphere, then the alfven 
> speed v_a is 80 kms and d/v_a is 1.2 sec. Fast.
>
> So I am really puzzled why you appeal to beams at all.  There is 
> certainly nothing in the iris data that I can see could ever be used 
> to give direct evidence for e- beams...  all I can glean from these 
> data is that there is a sudden release of energy under the place where 
> Si IV is formed.
>
> So I am very puzzled...
>
> Philip Judge, Scientist, HAO, NCAR
> 3037759863
>
> On Oct 30, 2014 2:49 PM, "Paola Testa" <ptesta at cfa.harvard.edu 
> <mailto:ptesta at cfa.harvard.edu>> wrote:
>
>     Dear all,
>
>     you might be interested in the following paper that has just been
>     published on Science:
>     "Evidence of non-thermal particles in coronal loops heated
>     impulsively by nanoflares"
>     It can be downloaded from astro-ph: http://arxiv.org/abs/1410.6130
>     or directly
>     from the Science pages:
>     http://www.sciencemag.org/content/346/6207/1255724
>     The abstract is below.
>
>     cheers,
>     Paola
>
>
>     Abstract:
>     The physical processes causing energy exchange between the Sun’s
>     hot corona and its
>     cool lower atmosphere remain poorly understood. The chromosphere
>     and transition region
>     (TR) form an interface region between the surface and the corona
>     that is highly sensitive to
>     the coronal heating mechanism. High-resolution observations with
>     the Interface Region
>     Imaging Spectrograph (IRIS) reveal rapid variability (~20 to 60
>     seconds) of intensity and
>     velocity on small spatial scales (≲500 kilometers) at the
>     footpoints of hot and dynamic
>     coronal loops. The observations are consistent with numerical
>     simulations of heating by
>     beams of nonthermal electrons, which are generated in small
>     impulsive (≲30 seconds)
>     heating events called “coronal nanoflares.” The accelerated
>     electrons deposit a sizable
>     fraction of their energy (≲10^25 erg) in the chromosphere and TR.
>     Our analysis provides tight
>     constraints on the properties of such electron beams and new
>     diagnostics for their
>     presence in the nonflaring corona.
>
>
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