[Loops] EIS AR Loops - Tripathi et al, 2009, ApJ/ some historical comments etc.

[Hugh Hudson]

Leon, why not look at the yellow line with one of these AO systems?  
They are more than 2X better than TRACE or XRT, and soon there will  
be ~1.5 m apertures. That would be faster than getting a rocket or  
satellite built.

Hugh

On Jan 8, 2009, at 1:03 PM, Leon Golub wrote:

> Dear Serge,
>
> It is useful to be reminded of the history and of the ground-based  
> data.
>   Still, I don't think that this contradicts my assertion. There is  
> some
> evidence from density diagnostics, from analysis of cooling loops  
> in the
> different EUV wavelengths, and from the SOT C IV data, that finer
> structures exist in the hot corona below the level we currently can  
> see
> in the EUV or soft x-ray. I'm afraid that the only way to settle  
> this is
> to fly a higher resolution telescope, going at least 2X better than  
> what
> we currently have. (Indeed, as Jean-Francois notes, EUI may do that on
> Solar Orbiter. But I'd very much like to see this done - even if it's
> only a snapshot on a sounding rocket - sooner.)
>
> Leon
>
>
> Serge Koutchmy wrote:
>> Dear Leon, Helen, Markus, Hugh, Jean-Francois, Joan et al.,
>> Regarding the fuzziness (also called the diffuseness, the lack of
>> resolution, the impression of smearing- I am not using here any
>> impressionistic terminology, just because colors are not involved in
>> your business), it could be interesting as well to recall some
>> historical observations and, apparently, basic facts. If you think  
>> this
>> is outside the scope of your Space and/or other research, please  
>> delete
>> this message and accept my apologize.
>> Loops (like the corona) were first observed, more than a century ago,
>> during solar total eclipses, in W-L. and we thought that we  
>> understand
>> at least a part of their physics (like being in hydrostatic  
>> equilibrium
>> based on their radial density variations) when assuming they are
>> stationnary.
>> Lyot coronagraphs permitted to easily image the inner corona in  
>> emission
>> lines and hundred of papers were written on loops. Lines were  
>> classified
>> in 3 classes (excellent representative are for class I: the red  
>> line of
>> FeX; for class II: green line of FeXIV and for class III: CaXV yellow
>> line which is seen, by the way, all the time in active regions-  
>> see the
>> routine measurements of SPO).
>> Classes correspond to roughly temperatures differing by a factor 2,
>> starting with the red line at 1 MK, almost without overlap in space
>> (uncorrelated). When the first good (photographic) images were  
>> obtained,
>> immediately the fuzziness of the Yellow line was noticed and more
>> importantly, that the FeXIV is fuzzier than the simultaneously  
>> obtained
>> FeX line images was established. I was at the Pic du Midi  
>> observatory in
>> 1971-72 when these images were taken by J-L Leroy and we had  
>> rather hot
>> discussions on their interpretation. We decided it is probably due to
>> instrumental problems, including seeing problems.
>> Again and after in the 80ies, thousands of FeXIV and FeX images were
>> taken with the former "one-shot" coronagraph of SPO, with improved
>> resolution (more than a solar cycle covered !) and discussing  
>> about that
>> with Ray Smartt and many others, we could not exclude an instrumental
>> effect. What was noticed is that interacting loops were seen more  
>> often
>> in FeXIV, and higher in the corona.
>> Later, came the Norikura team, boosted by the success of the  
>> Yohkoh SXR
>> imager. They again confirm this famous effect. Let me give you the  
>> exact
>> reference of a paper already written in the "Space age" in ApJ:
>> Ichimoto, K. Hara, H. Takeda, A. et al 1995, ApJ 445, 978 and extract
>> the interesting statement made p. 979: "...because the 3 emission  
>> lines
>> (FeX; FeXIV and CaXV) are observed with the same optical system, we
>> beleive that the diffuseness of the hot components compared with the
>> cool components IS A FIRM RESULT."
>> Everybody knows of course the wonderful Trace 171A images of the 1 MK
>> component of the corona, with loop systems, which were definitely  
>> better
>> of quality (sharper) than what is obtained in hotter lines, using THE
>> SAME instrument. Even FINER loops are seen in much cooler lines, like
>> the Hapha or Lyman alpha line, starting from the drawings made in  
>> 1870
>> ies (yes, not 1970 ies), and after, photographic images taken at
>> SacPeak, rocket images from TRC, etc. and more recently CCD images  
>> and
>> movies taken with the La Palma SST and Hinode.
>> Everything written tells us that the impression we get from an  
>> image is
>> subject to a false interpretation when instrumental parameters are  
>> not
>> taken into account. Resolution is not a matter of just pixel size.  
>> It is
>> mainly a matter of signal/noise ratio over the feature you  
>> consider and
>> even the signal alone is "noisy", just because the lack of  
>> photons; this
>> is at least my understanding after observing during more than 40  
>> Years
>> and you can disagree.
>> Now coming back to the W-L observations let me notice that:
>> 1- The hotter is the loop, the higher it is (see also the V-R scaling
>> law). The heating makes the temperature higher when going radially
>> outwardly up to 0.3 to 1 solar radius from the surface. The important
>> factor is that the radial gradient is higher in cooler loops  
>> compared to
>> hotter loops. It is of course what the hydrostatic law shows (on W-L
>> images). The scale height of cool loops (FeX; 171A etc) is roughly  
>> 50000
>> km; it is 100 000 for FeXIV. This is what you get analyzing W-L  
>> images
>> assuming the loop iso-thermal and computing the radial gradient. Of
>> course the higher is the gradient, the sharper is the image.
>> 2- Talking now about the transverse gradients, the interplay  
>> between the
>> magnetic pressure and the gaz pressure should be considered. The  
>> beta is
>> decreasing when going up to the heights of hot loops (and further
>> opening up due to the wind, see eclipse images). It makes transverse
>> gradient weaker for hot loops. Accordingly, cool loops will look  
>> sharper.
>> This is instrumental effect.
>>
>> In this naive analysis made by a lambda eclipse/coronagraphic  
>> observer,
>> I do not see nothing wrong in having hotter loops fuzzier and I do  
>> not
>> see the urgent need to introduce an additional filling factor, as  
>> far as
>> we use good images giving large aspect ratio of loops. What is  
>> needed is
>> a more sophisticated diagnostic, like the spectroscopic diagnostic  
>> which
>> would include the line profile analysis to measure the Doppler-Fizeau
>> effect. In addition we need the temporal resolution to look at
>> transverse waves of shorter periods... there is a bright future for a
>> new groundbased large aperture coronagraph which would permit the  
>> access
>> to these diagnostics. Improving the W-L and visible monochromatic
>> imaging in Space (inner corona; fast imaging; higher resolution;
>> polarization) with an ASPIICS space mission which produces artificial
>> eclipses during several Years could be the ultimate. For the  
>> moment, I
>> guess SDO with its 4K coronal imagers of improved resolution will  
>> bring
>> a lot and I am sure it will indeed bring a complete renewal of the
>> topic. This is what you told us and let's hope it will be launched  
>> in 2009.
>>
>> Thank you for reading this up to the end (almost). Let me wish you  
>> all
>> the best for 2009 and use the attached season's greeting coronal  
>> image
>> for that, including the caption I put after.
>> (apologize to those of you who already got it).
>> S.
>> -----------------------------------------
>>
>> BEST WISHES FOR A HAPPY 2009 NEW YEAR !
>>
>> Enclosed is a seasons’greetings compressed composite that we did  
>> using
>> some new observations from the Pic du Midi Observatory CLIMSO
>> instrument: a CaII-K line disk and a coronagraphic H-alpha image,  
>> same
>> scale, but obtained 2 s later, in the very late afternoon. No  
>> activity
>> during this surprisingly extended solar minimum. However here the  
>> solar
>> disk was near the W horizon, at the time when the daily Madrid to  
>> Zurich
>> Airbus 320 was passing by… It is the 1^st time the infamous aircraft
>> contrails are imaged in “emission”, using grazing incidence rays near
>> the H-alpha line. Would it be solid particles producing additional
>> pollution ?
>>
>> We believe some new type of propagating waves was revealed using  
>> these
>> unique coronal observations, although a definite Doppler-Fizeau
>> signature is missing. Note that the heating process due to their
>> dissipation in the Earth atmosphere was not taken into account to
>> explain the not less infamous global warming because waves  
>> possibly also
>> accelerate the rather cool Mistral (a well known wind in the South of
>> France)...
>>
>> Take care.
>>
>>
>>
>>
>>
>> Leon Golub a écrit :
>>> Helen et al.,
>>>
>>> I can't let this go uncommented. Even though this paper was accepted
>>> (I know, I was the editor) I disagree with the conclusion
>>> that hot loops are fuzzier. Yes, that's what you see, but it is
>>> also explainable if the hot parts of the AR have many fine threads
>>> (unresolved at present resolution) with a large filling factor.
>>> That as the conclusion Joan and I came to from analyzing 284A
>>> data.
>>>
>>> Anyway, this won't be settled until we fly an imager with higher
>>> resolution. We're proposing one this year and I'm hoping we get
>>> the chance to clear this up, finally.
>>> Cheers,
>>>
>>> Leon
>>> _______________________________________________
>>> Loops mailing list
>>> Loops at solar.physics.montana.edu
>>> https://mithra.physics.montana.edu/mailman/listinfo/loops
>>>
>>>
>>
>>
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+++++++++++++++++++++

In medias res
hhudson at ssl.berkeley.edu
+1 (510) 643-0333

AST:7731^29u18e3



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