Solar Cycle 24 Group I
From RHESSI Wiki
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- | == Session 1 == | + | == Session 1 What are active region coronal loops? == |
+ | === Ignacio Urgate-Urra === | ||
Future active region future obs hinode etc...Thurs? | Future active region future obs hinode etc...Thurs? | ||
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First question: | First question: | ||
Where is the pinot noir?! | Where is the pinot noir?! | ||
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What are coronal loops? | What are coronal loops? |
Revision as of 20:38, 11 December 2008
Session 1 What are active region coronal loops?
Ignacio Urgate-Urra
Future active region future obs hinode etc...Thurs?
First question: Where is the pinot noir?!
What are coronal loops? -Why they reach temp, evolve, structure? -Do they actually reach these values?! -Is there a typical loop? -Common loops? -Do scientists agree? -What do models need from observers?
Helen: Does a loop have to return to the sun? How big? Markus: Don't see loops in open regions? Helen: Should we only be interested in loops or active region as a whole? Markus: Large loops and scaling laws can produce fan like-not closed loops eg TRACE. Hardi: 90% energy goes into flow. Open field lines factor 100 reduced in intensity. (Leer). George: Bigger flows = dark loops.
-Temp structure is time dependent, cooling - etc
Helen: are apparent single loops really loops?
Do loops cool in the same way?
Dynamic loops, flare loops
What temp do they reach - xrt - Ko (09)
Static vs Dynamic
Pre-SOHO (Klimchuk 08)
Soft xray loops - life times longer than cooling time.
BUT
Dynamic SXR component Transient brightenings - EUV counterparts - xray loops cool to EUV -Tsuneta 94- Shimizu 94 concludes that microflares observed by Yokoh alone can't heat active region corona. Does this rule out Parker nano flares? Need more sensitivity ie XRT. -Microflaring is important even for long lived loop.
Different phases - steady AR, Implusive AR, QS Hardi: Are phyical heating mechanisms in different phases the same steady AR, Implusive AR, QS?
EUV loops -Warm 0.5 < T < 1-3Mk -Over dense -Super hydrostatic scale heights - impulsiveness - TRACE loops densities are higher than hydro equilibrium.
How are EUV loops related to XRT loops? XRT loop lifetimes are longer than cooling times
-There is a subset of loops with T<1Mk
-These loops host slow waves
-Coronal rain, thermal non-equilibrium, steady footpoint heating.
STRUCTURING
-are loops monolithic?
-have we seen elementary strands?
-smooth temp and density across loop axis
-smooth temp and density across strand axis
Markus: loop strands > 1500km are composite
Believe individual stands have been observed by trace.
Multi stands at same temp would be monolithic very unlikely.
-are they multi-stranded? Warren paper. -Ugarte-Urra 2009 cooling times - individual loops?
Would super high resolution TRACE show fine structures -Fine scale in chromosphere may not necessarily be reproduced in corona due to temp dependence gyroradius etc - Markus, Hardi.
Multi-thermal Filter analysis Spectroscopic analysis - narrow DEM - previous broad DEM (Schmeltz)
Implications for heating
-nanoflares
- convection - braiding -stress - reconn
-PRO: impulsive, explains overdense, multi-strand, broad DEM
-CONS: not seen (yet), monolithic loops, no obsrved braiding
- Nano flare storm - narrow DEMs
Hardi: Cons not necessarily cons - Events overlap enough for apparent continuous distribution.
-chromospheric heating - Reconn at chromospheric level - Cross field diffusion more efficient -> coherence - Poss explanation for outflow/waves
- open questions - Coronal heating can explain - upflows chromospheric evaporation - How much dissipation at low heights goes into heating corona - Radiative losses?
-Cons: Hinode no mixed polarity in plage
-Debate shifting to heating localisation
Is there a typical loop - Maybe?
Do loop share common properties - No
What do models need from obs - need to provide
Need spectroscopic + time dependent properties of multiple loops AR.
Hardi: Need coronal magnetic fields