Solar Cycle 24 Group I

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Group I 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.


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

Joint I+C Session 2 Coronal loops and the slow solar wind

Scott MacIntosh Into the Corona with CoMP

CoMP 3 lines - 1 corona 2 chromosphere Full stokes vectors Fe XIII

1 hour observations -Static off limb observations in intensity - line width -Doppler movie shows outward propagation of waves. No compressive/intensity signal.

-Phase speeds of 1-4Mm/s -Amp 0.25-0.5 km/s -Power spectra show dominance of 5-min periods. -Deduce observations of coronal Alfven waves.

Time-distance seismology of the corona Tomchzk 07, Tomchzk & McIntosh,08 -Previous analysis insensitive to angles > 65 degrees

Tracking in 2D -Time-Distance time series -Coronal k-omega diagram -Detection of upward and downward waves -greater amplitude of upward waves -Original analysis phase speeds were factor of 2 too large. Now 650 km/s

Aschwanden: Comparison to kink mode intepretation

Question of why line of sight integration does not smooth out observations of these waves?

George Doschek Active Region Flows Observed by EIS

EIS has slit and slot observing modes Long wavelenth band spectrum -About 50% of lines are new - not included in chianti -may be important for irradiance studies -Lines only observed in skylab flares observed routinely with EIS -EIS allows new observations of non-thermal line width -TR & coronal lines are greater than theory predicts - reconn, bulk flow, MHD waves, other?

Non-thermal motions - what is known -Average V vs T is known -Average V with hight about the limb is known in some cases.

XRT continous upflows of plasma in loops -Apparent upflow ~140 km/s -Occur in darker areas of active regions, correlated with non-thermal width -line width and centroid shift correlated

Doschek, 2008 -Temperature structure to the flows -multi flow components, two component flows in line profiles.

General properties of an outflow region -multi component centroid shifts -flow velocity-masking allows outflow regions to be indentified spatially.

Mason: What do more obs of these kind of regions tell us? Doschek: Return statistical sample of observations.

Doschek: Brighter active regions would allow observations in more lines.

Modelling contribution of active regions to heiospheric field. Do EIS upflows flow along oped field lines and contribute to solar wind?

12 may 07 13UT EUVI upflows & EIS Doppler map.

Mass outflow flux -Spicule mass flux 1.7x10^-9 g/cm^2/s -11 Dec 10^-5 g/cm^2/s for Doppler speeds > 12km/s and 1.6x10^-6 g/cm^2/s for Doppler > 30 km/s

Use PF extrapolation combined with Doppler flow to determine flow velocity.

Mason: Are PF extrapolations available. DeRosa: PFSS available in solarsoft. Based on MDI magnetograms. 1 degree resolution. ROI extrapolation available. Peter: Should be careful using these extrapolation - different alpha.

Wrap-up Outflow out of the room!

Joint I & G session 3 Dynamic Heating in Active Regions

Helen Mason AR loops - observational constraints on heating

-Are quiescent 1Mk loops isothermal multi-thermal along los? -Is there a weak high temp component of all AR loops? -Loops appear fuzzier at high T, is this real or resolution? -What are densities and filling factors of a coronal loop, length varaition? -How does temp vary with loop length? -What is the plasma flow? -What are moss physical properties? -Do hot dense core loops interact with larger cooler 1MK loops?

Intensity, veloctiy, line width maps Hinode alows detailed maps of density, temp, flow, line broadening Young, 07 Doschek, 08 AR map Dec 2 2006 took 5hrs -However rastering is slow, need carefully designed EIS sequences. -Velocity rest wavelength from QS average.

Flows at different temperatures Del Zanna 07,08 -Low temp red shift, high temperatures blue shift on order 20 km/s, persistent over days. -Line blending difficulties when using EIS, refer to EIS team for blend check.

EIS obs 19 May 07 Tripathi Tripathi 08 -Measure flows simultaneously at temp from 5.6MK (Fe VIII) to Log T = 6.4 (Fe XV) -Red shifted flows at cool temp Si VII -Blue shift at higher temp Hardi: NeVIII temps are generally blue shifted in QS, can affect wavelength calibration. -loops are sharply defined at low temp, but diffuse at high temp. -Are hot loops really fuzzier, or are hot background loops clouding the view. - needs to be quantified with EIS.

Temperature along the loop - EM loci method -Temp rises from 0.8MK at base to 1.5MK at top, mildly multi-thermal. In press -Doschek: if lines cross means all lines can be explained by one emission measure -> isothermal.

Electron densities along loop -Electron densities at base 10^10cm-3 and 10^8.5 cm-3 higher up. -Mg VII seem lower than FeXII and SiX. Low filling factor 0.02-0.05 at log T 6.1MK and close to 1 at log T 5.8MK at the footpoint. Sarkar: if low filling factor why close to isothermal.

AR focus on core -Fe XII 200x200" 20min raster 10s exposure -Active region moss at different temperatures -Density in core of AR can be as high as 10^10.5cm-3 -Density is highest at temp of log T = 6.1 -High densities are in the +ve polarity regions not the sunspot side -Density correlates well with magnetic field.

Limb active region obs odowd mason .. unpublished -Dec 17 2007 -Temp and density as function of height above AR -Electron density peaks in core of active region and drops above limb.

Need mult-stranded models What about hot dynamic cores? Could flux be submerging? Are we in equlibrium? Need atomic data.

Susanna Parenti EUV signatures of small scale heating in loops

Nanoflares -hard x-ray and EUV nanoflares -observed small scale brightening -nanoflares in loops -not resolved -loop made of multi-strands

Energy disribution -Hypothesis- Energy freq disrib same as... plama response

Model -power law distribution with index alpha=-1.6 -cooling model

Results -thermal energy heating function better recovered if cooling is thermal conduction -Synthetic spectra similar results, but different behaviour at lines at diff temp. -Best line candidates are > 3MK.

New results Parenti & Young 08 -Stat distb of lines Li isoelectronic sequence. -Comparison of pdf of EUV emission changes with wide/narrow band instrument.

-Simulation -multi standed 2000 -nano flare power las alpha=-1.7 -EIT SUMER response function

-Narrow band instuments -different power law (steeper) than heating function recovered.

-Wide band instruments EIT 171 FeXII EIS -Different power laws than heating function recovered again

-Hot lines Fe XIX index -1.7 -Fe XXIV -1.4

Conclusion -Shape of pdf of EUV lines depends on iso-electronic sequence -wide band istruments affect pdf shape of EUB lines -Confirm high temp lines preserve heating function (also Li-like) -Useful for SDO, Orbiter. High temp channels may bring insight.

Questions: Markus: Confirm EUV observations.

Helen: Fe XIX from CDS found -1.7

Paolo: How is energy dumped in the model. Susanna: Impulsive spike input. Delayed input doesn't change much. Hardi: Could add diagnostics to test? Energy at small grid/time points launch waves which travel through lower temp regions. Observe line shift with spectrometer. High temp cause may have low temp diagnostic signatures. Look for chromospheric evaporation upflows.

Group I Session 4 Diagnostics in Active Regions: I Observations

Peter Young Active region diagnostics with EIS

Line fitting Paris tutorial [1]

Multiple gauss fitting tool

Velocity needs to be corrected for: -Slit tilt -Orbital motion -See tutorial

Line width -Instrumental width 55mA - varies along slit 1-3mA

Active region maps -significant velocity signals away from bright active region structure. Del Zanna 08, Hara 08, Doschek 08.

-Possible to arrange higher telemetry rate with other instuments to take large rasters.

Loops -Velocity and line width maps don't always overlap completely with intensity loops. Even anti correlated examples. Possible similar effect seen in CDS Stein Vidar software note?

Temperature diagnostics -observations of different ionization stages of an element.

New FeIX lines -171 is not scientifically useful for EIS due to low intensity. -New line identified (Young arXiv 0810.5028) -Most useful line is at 197.86A Fe IX (unblended) peak of effective area -197/171 good temp diagnostic (req long exp for 171) -Fe VII atomic data Witthoeft & Badnell, 08, allow Fe VII do be used in DEM analysis. -ar_velocity map study AR seen in 11 Fe lines. -FeXIII line intensity as Ne not Ne^2 - intensity map has less dynamic range.

Density diagnostics -EIS allows routine high precision density diagnostics -most useful FeXII FeXIII, Mg VII -Fe XII Fe XIII

Emission line fitting -need robust method for auto fitting -take care with blends

Spectral tilt -lines at shorter wavelength are slightly higher on the CCD. -Only 0.65 pix for FeXII but has significant effect on derived densities.

Low density dataset -Fe XII-XIII give density ratios different densities in loop measurement.

High density dataset -Again differnce in density ratios

Sources of discrepancies -atomic data - different temperatures -can background subtraction resolve discrepancies - No still remains after background subtraction.

Column depths -can be measured from line intensity nd derived density. -assume isothermal plasma, coronal abundance

FeXII and FeXIII -discrepancies need to be resolved -1. Atomic data needs to be re-evaluated, 2. comparison with SiX

Mg VII 278.4A density diagnostic -lines formed at log t= 5.8 very useful for TRACE 171 type loops -density in footpoints Young (2007, PASJ) 25s exposure.

FeXII 3hr sit and stare study across loops

List of EIS studies still to be done -What is relation of intensity, velocity, line width in loops. -Can EIS see oscillations in TRACE loops. -How do temp and density vary along loops? -Nanoflare distribution using FeXII 195?

Group I session 5 Diagnostics in Active Regions: I Observations Cont...

Markus Aschwanden Instant Tomography of Active Regions

-Stereoscopic reconstruction of active regions with STEREO -Only requires 2 frames -Available in solarsoft

AR 9 May 2007 -Images coaligned and high pass filtered -High pass filter selects finer loops w<3 pix, 4% flux; w<7 pix selects larger loops.

Image preprocessing -Selective filtering -Image stacking to increase s/n before filtering -EUVI resolution doesn't resolve TRACE loops.

Stereoscopic 3D reconstruction -Manual clicking of selected loops in A & B -Epipolar method -Spline fit selected points

-~30 loops fitted in AR -Height errors are along the line of sight -Fitted loops aren't coplanar

Hydrostatic Modeling -3D loop geometry can be used to model hydrostatic scale heights, inclined loops are visible along their length.

Density and Temperature Measurements -Determination can only be made after background subtraction. -Background selection has large effect. -Loops cross-section profiles are extracted and background modelled with cubic polynomial interpolation. -Triple filter temperature analysis. -Temperature profile along loop dervied using 3 filter ratio. -Input: Background subtracted loop flux profiles -Output: Electron density and temperature profiles. -Derived approx constant temperature profiles along loop, in comparison to spectroscopic results presented yesterday. (Mason, Young).

-Colour map of loop temperatures, hottest loops tend to be smaller.

-Density profiles along the loops are consistent with gravitation stratification of hydrostatic loops. -But densities are not consistent with hydrostatic equillibrium soloutions, as in previous TRACE EIT results. Overpressures, implies observed cooling phase. -Different observed loops warm, cold etc are different phases of loop cooling evolution. -EUV loops are generally observed during loop cooling phase

Image preprocessing: Multi filter loop tracing -3D reconstruction of 100 loops 1-2MK

3D field interpolation -skeleton field - triangulated loops -3D field - weighted interpolation

Tomographic rendering -Interpolated 7000 field lines filled with exponential function until best match of 3 filters is obtained. -Forward fitted AR model. -DEM distribution of FF AR model similar to Brosius, 96 measurements.

-FF AR model yields super-hydrostatic scale heights for T<3MK

-Comparison of stereoscopic loops show significant diffences to PFSS model.

-Ref Instant Tomography of Active Regions, 2008, ApJ, Submitted

Ignacio: All loops evolve steady xray loops, EUV loops, Markus: Cooling times on order of 30mins.

Hardi: Impulsive heating isn't necessary to reproduce density temperature cycle. Can be reproduced with constant footpoint heating eg (Muller).

How can impulsive and steady heating be diagnosed observationally? High temperature ion formation required for impulsive heating mechanism?

Group I session 6 Diagnostics in Active Regions: I Observations Cont...

George Doschek AR properties observed by HINODE

Possible Japanese solar C A: Out of ecliptic B: Super HINODE SOT type resolution in corona

Structure of transition region -Sub arcsec structure -structures appear same at different temps -> unresolved -SUMER observations show broadening -> strucutre tenths arcec -TR dynamics connection between lower and upper TR is unclear.

Sit and stare wave observations with EIS Mariska et al. 2008, ApJ, 681, L41.

Wide slot movie dataset 28 Apr 07 2 days 15s Cadence Fe XV 2.2 x 10^6 K

EM Loci plots show sharp 1.4MK temperaure above limb with SUMER

Bright point filling factor <<1 -> sub resolution BP filaments Dere, 2008, A&A Submited.

Flares -Best current flare observations with EIS (Hara, 2008, PASJ, 60, 275) -Measurement of Doppler shift and non-thermal widths, syphon flow... -Waiting for flare observations with EIS -Possible to observed large flare velocities in slow mode in dispersion direction. -Multi-thread model can account for BCS flare lightcurves Warren & Doschek 2005. -Testing loop heating models requires spectroscopic diagnostics, necessary to observed hight temperatures Warren 2008, ApJ, 685, 1277; Ko et al. EIS & XRT

CaXVII less blended in flares, can deconvolve emission. Ko, Warren, Doschek, 2008. Blends with multiple OV lines and FeXI. -OV an EUV hard xray proxy EIS/SUMER Muglagh, 2008. TR temperatures are anomalyously high to excite high temp OV lines on order of 1MK - high energy tail of maxwellian distribution. Possibly excited by non-thermal particles. -Image emission deconvoloution by FeXI image intensity subtraction to obtain CaXVII -Algorithm available for observers in solarsoft.

Comparison with Markus's results using EIS

Richard Nightingale High resolution of temp density and with profiles

-Measured temp, density, width profiles of 243 loops using triple filter TRACE data -Apply loop scaling laws and hydro models to profiles, using 3D geometry. -Using similar method to Markus's talk.

12 fitted 3D loops -temperature profiles relatively flat along loops. -Densities show increase towards loop apex. -loop widths perpendicular to lenth along loops. Approx constant cross section along loop length. Constistent with Klimchuk results.

-Loop geometries for all 243 loops -loop half lengths 56+-47Mm -temp 1.18+-0.3MK -Average electron densities ~10^9 cm-3

Over pressure Vs loop half length -ideal gas/equilibrium models -> over pressures.

-TRACE results show over-densities and flater temp profiles than RTV law (Ashwanden, Nightingale, Alexander, 2000) -TRACE loops appear with time delay in 171 and 195 winebarger cooling phase

Conclusions: -Under pressure loops in heating phase are observed <20% of time, majority in cooling phase. -Over pressure consequence of non-equilibrium cooling phase. -Estimate loop lifetime of 10min-1hr for sample of TRACE loops

Group I session 7 Diagnostics: II Forward Modelling

Pia Zacharias Flows in Hot Coronal Loops

Doppler shifts in the solar transition region red 6km/s and blue few km/s corona. Transtion point log t 5.7

3D simulation of Doppler shifts. -Observation and simulation discrepancy for coronal lines -Input QS magnetic field -3D MHD -Spectral synthesis -> resulting loop structures in C4 -> Doppler maps - mean redshift, FWHM 3x smaller than observations

Global mass balance -Is the model coronal mass sinking? -Coronal mass fluctuates ~0.1% log t > 4.1 -Not due to mass loss -Variation due to heating

Investigation of hot loops -Nature of flows in hot and long loops -27% siphon slows -62% draining downflows out of loop -10% stange flow profiles

Heating loops with upflows? -No hot loops with upflows found.

Prob -Even loops that are heated up are draining.

Outlook -Properly follow fieldlines in time -What about upflows seen in Dopplermaps? -Investigate cool loops T<10^5K with same lenghts

Ignacio: What observations do we need to test these models?

Hardi: Run experiments on scales comparible to the Sun, limited by grid resolution size. Resolution on the scale of photospheric driving. Fast raster to study evolution of Doppler shifts. Make simulations available to public>

Sofiane Bourouaine Coronal Loop Model Including Ion Kinetics

Do we need micro-heating to understand loop heating?

Loop observations - warm loops (Lenz, 99) -Flat temperature profile - concludes isothermal 1.2MK

Loop density -Warm loops overdense <2MK, hot loops >2MK over dense (Winebarger, 2003)

Loop Width -Hot loops >1.5MK loop expansion factor ~1.13 -Cool loops no expansion factor (Klimchuck, 2000)

Modeling should address -Energy source, Conversion mechanism, Plasma response, Plasma emisson.

Heating of coronal loops -Macrophysics AC/DC -Microphysics

Can coronal loops be heated by collisions? -Assume typical plasma parameters in upper chromosphere -Dissipation rates can be estimated -To explain heating must balance radiative cooling. -> Impossible to heat chromosphere by collisions.

Why we need a kinetic description of coronal loop plasma. -corona weakly collisoinal -heating mechanisms operate on smaller scales that particle mean free path -classical collisonal coeffs not large enough -Wave particle interaction may be possible scenario for loop heating.

Kinetic model for a coronal loop -loop geometry -symmetric/non-symmetric heating -Multi-ions plasma loop -temperature anisotropy in oxygen ions, isotropy maintained for other species -Expansion -> more heating than no expansion case

Wave absorption mechansim -gyro freq decrease with expansion -> ion heating scale height is larger, greater heating

Conclusion -Ion heating has strong spatial connection with loop cross sectional variation

Aveek: How can these be observed Sofiane: Direct observations not possible

Group I session 8 Diagnostics: II Forward Modelling

Helen Mason for Susanna Parenti The role of Imaging and Spectroscopy for the importance of understanding coronal heating

Non-equlibrium ionisation stages may be important for nano-flare heated loops.

Buchlin et al. 2008, Simulation of observables for MHD turbulent heating.

Reale et al. 07 XRT multi-filter temperature analysis

Flows in loops Spiros & Jim,06 modeling of upflows at high T Observations: downflow at TR temp, Dammasch,08

AR thermal structure in EUV/UV 3 peak temperature components

More work to come

Aveek Sarkar Temperaure determination using EUV imaging of a nanoflare heated loop

Hydrodynamic simulation -125 strand model

Setup -10Mm loop -0.5Mm chromosphere on both sides of loop -strands randomly heated by nano-flares -heating distribution power law -2.3

Output for each strand -T, density, velocity -summed over each strands and divided by n^2 -EM weighted avg temperature -find cool plasma blob formation which flow up from footpoints

Apex and footpoint heated profiles produce ~isothermal profiles

Combined filter ratio (Reale et al., 07) -Combinded improved filter ratio CIFR uses fixed ration and will always find the same temperature. -CIFR is biased towards isothermal results

Day 1 Summary

Sessions 1 & 2

What are the key questions? What are the open questions? What is new? What do we need for the future to answer these? Missions/models..etc.


* 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?

Warm loops, hot loops, "static" loops, impulsive loops.

Day 2 Summary

Sessions 3 & 4

What are the key questions? What are the open questions? What is new? What do we need for the future to answer these? Missions/models..etc.


Summary day 2

--Mmarsh 21:29, 11 December 2008 (UTC)

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