Solar Cycle 24 Group I

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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

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