[Loops] loops and thermal nonequilibrium

[Tongjiang Wang]

Dear Leon and Piet

Thank you very much for your comments and suggestions. Yes, I agree it is
important to determine whether those propagating wave (or upflow) features
are only seen in the cool loops (evident in TRACE or EUV 171) or they may 
be existing in hot loops. Whether the propagating speed depending on the 
temperature of the loop may provide additional evidence to tell the truth. 
I wish SDO/AIA will be successfully lauched next year and can 
significantly contribute to solve this question.

But whatever how obvious the flow patterns look like, the feature of 
clear periodicities of this phenomenon should not be negligible,
and need a reasonable explanation.

Hope I can find a chance to visit Harvard-Smithsonian Center some time.

Merry Christmas and Happy New Year!

Tongjiang

-------------------
Tongjiang Wang

NASA GSFC - Code 671
Bldg 21 - RM 177B
Greenbelt, MD 20771

Tel. 301-286-6575
Fax. 301-286-1617

On Tue, 22 Dec 2009, Leon Golub wrote:

> Dear Tongjiang,
>
> I see that this subject is going to be debated for many years to come, which 
> is good. We'll have to discuss this in person some time, where we show each 
> other the observations and both be looking at the same thing. In particular, 
> it is exactly in those fan-like features that we see the clearest flows, and 
> indeed there is some question about the temperature.
> We need simultaneous observations, in the same spectral lines, with EIS and 
> AIA. These should be available in a few months, once SDO launches. Since 
> TRACE sees upflows at both ends of the large loop systems, it seems likely 
> that there are interlaced loops (or threads) and that the flows go up warm 
> and are cooler coming down. With low-resolution (~1") imaging, it would seem 
> as if the blue shifts and red shifts are on top of each other, but this is an 
> illusion cause by failure to resolve the different structures.
>
> Leon
>
> Tongjiang Wang wrote:
>>  Dear Leon,
>>
>>  I just would like to remind you that the regions showing tens of km/s
>>  upflows seen in EIS coronal lines are typically for weak or dark fan
>>  structure in TRACE and XRT, while the propagating wave features are often
>>  seen in bright fan-like loops (like those shown in my paper,
>>  where the brighter part of fan loops show RED-SHFIT!). Indeed there are
>>  other EIS observations show bright fan-like loops show redshift while
>>  not blue shifts. Moreover, as you mentioned the steady flow is not
>>  possibly seen in imaging observations, that means that the moving brobs
>>  features correspond to episodic jets or pulsive flows, thus Doppler shift
>>  fluctuations of tens of km/s amplitudes are expected for a upflow of
>>  100-120 km/s for fan-like loops with a typical inclination of 50-60 deg
>>  (see Marsh et al. 2009 who derived the inclination from STEREO/EUVI obs),
>>  but my study did not
>>  show this is the case. Finally, in the dark region showing tens of km/s
>>  EIS blue shifts, the waves may co-exist with upflows, therefore, the
>>  upwards moving blobs are not necessary to be the upflows. I'll try to look
>>  for more examples to support my view. Thank you for your discussions.
>>
>>  Best Regards
>>
>>  Tongjiang
>>
>>  On Mon, 21 Dec 2009, Leon Golub wrote:
>> 
>> >  Dear Tongjiang,
>> > 
>> >  This is exactly the "argument" I've been having for the past ten years, 
>> >  starting with Nakariakov in 1999. I've been waiting for the Doppler data 
>> >  since then, because where I see flows, other people see waves. I do 
>> >  think that the EIS results are now showing higher velocities of some 
>> >  tens of km/sec, and in TRACE the flows do start out slow at the 
>> >  footpoints, so there's no inconsistency with what you're saying about 
>> >  the speeds. There is a difference in that EIS sees the upflows at 
>> >  somewhat higher temperatures than we do with TRACE, and XRT sees them 
>> >  too, meaning higher T. I'm hoping that AIA will help sort this out.
>> > 
>> >  What I can tell you is that when we see waves in the corona, they are 
>> >  quite clearly periodic and there's no doubt about it. Just look at any 
>> >  movie (with high time cadence) taken above sunspots: it looks like a 
>> >  loudspeaker pulsing away. These fans are different, and if you look 
>> >  closely at your time-distance plots, you'll see the lower portions 
>> >  curving upward, as the flows accelerate on their way up.
>> > 
>> >  Leon
>> > 
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