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Took a slightly different approach than Tetsuya and Louise. I talked to NASA about giving press releases, and they want to know what major problems you've solved!
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One of the probs at NRL we've been working on is AR loops.
If we could say how loops are really heated, we could go far towards solving the coronal heating problem, and that's a press release that NASA would really be interested in.
We're in the "middle" of modelling them. The real important thing we have is the density, so we can check models of heating and cooling of loops. Most of these loops are not in equilibrium. By measuring the densities in the cooling, we can really check models. Seems now that the most common model for things like Fe XII is that it's a loop around 1.5 MK. The kind of theory that best explains the observations is a loop made up of strands that heat and cool sequentially in some sense explains why they last longer than the cooling time. You can also measure path lengths when you have the densities, so you can tell if you have unresolved structures.
Warren et al. 2008 Apj 686 L131
The loops seem to cool together, so the DEM doesn't get very wide.
Loop filling factors are about 10%. The densities from Fe XII are about 0.5 dex too high versus Fe XIII. So it's critical to do the atomic physics for these ions better, and to check them against densities from other ions, like silicon.
So we get these tiny fillin factors, but they seem to be doubtful.
IN summary, though, we have tremendous progress, but we're left with some big questions and need to improve the atomic physics.
IUU made a slot flare movie: loop models; it would be good to make serious progress by the time of the senior review.
We observed Ca XVII and we can now separate it out from the Fe XI and O V blends. It can now be used by people much more reliably if you know what you're looking for. YKK has developed a procedure for unfolding these that soon non-spectroscopists can use to use this 5MK line, so it extends the DEM temperature range posible from EIS. We didn't appreciate this blend when we picked this line, but glad we picked it; we didn't appreciate the density sensitivity either. Didn't appreciate the fact that lower TR lines like O V and VI are reasonably strong in our data, because Skylab only saw O V lines in flares: change of principle quantum number, so it takes a lot of energy. Those things have been a surprise, but making progress.
Here's another example of unfolding the Ca XVII emission. Can extend our analysis of ARs to high T.
Louise and Tetsuya mentioned flows, and those come from regions that are normally dark. The Fe XII intensity shows wide, shifted lines in dark areas. XRT also seeing this sort of thing, but you don't know if you're looking at a flow or a wave. John and Harry thought they were waves, but they turn out to be flows. They're over extended regions. You also see them in these broad regions.
When I sent a paper in on this, I think it was reviewed by people who worked in the heliosphere. e.g. Liewer, Neugebauer & Zurbuchen 2004 (SoPh 223, 209) who expect flows at the edges of active regions.
Haven't been able to link the flows to colder material. They occur where the field is more or less monopolar, but don't know if these field lines are really going into the heliosphere or just form long loops.
They're also a f(T) and many active regions have a blue-shifted flow component. You therefore get a correlation between the flow velocity and the width.
John Mariska has found waves in coronal loops. These waves present a problem, becuase they don't fit a strand model: so how can you see a coherent wave feature across the whole loop?
Also in ARs, if you look at SUMER data in the corona and make a Jordan loci fit, you get a single temperature of 1.4 MK. But when you go on the disk, you don't see that at all. need to work on this to try to resolve it.
Quiet Sun has been really quiet. KPD finds <<1.0 filling factors in bright points. Really important ot understand what the densities really are.
We've been lucky to __see__ flares. We've only seen one limb event (20061217). We'd like to see inflows. We really need to see a bunch of M flares. Observe the sites of evaporation and footpoints and see if they correspond to the general standard models that people have for flares.
When we see the footpoints, we can actually see evaporation.
We can probably do a lot more on polar jets; many more observations would probably be very useful to have as we're the only ones who can observe their properties.
Finally, EIS-SUMER campaigns: we wanted to calibrate EIS with SUMER if we could. With EIS and SUMER you get an isothermal corona. If you apply the calibration, they agree within instrumental errors. But the atomic dat for EIS are a little more messy. We have very little checks on ionisation balance. We measure temperatures well above the ionisation equilibrium temperature. The longer we can't figure it out, the more interesting it becomes. Perhaps non-thermal particles penetrate into the TR? That would be extremely interesting. Enrico Landi put recombination in, even though they're Li-like, and so simple. So we can make more measurements like this.
Finally (finally), something we can do is measurements with STEREO. Aschwanden is doing a lot with STEREO, but hasn't yet got involved in EIS.
A summary of what we ought to be doing.
* what are filling factors in loops
* do nF models work in loops
* do flows go into the solar wind
* how hot ARE active regions (Ca XVII)
* analuysis with SOT of EEs
* Check the standard flare model
* many problems in CHs.
There are several kinds of problems we can attack.
This page (revision-83) was last changed on 02-Feb-2017 13:19 by David R WilliamsTop