An IRIS view of the chromosphere and transition region and their connection to the corona - Bart De Pontieu and the IRIS team Lockheed Martin ...
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An IRIS view of the
chromosphere and transition region
and their connection to the corona
Bart De Pontieu and the IRIS team
Lockheed Martin Solar & Astrophysics Laboratory
IRIS data products
Mg II wing 2830Å Mg II k 2796Å C II 1330Å Si IV 1400Å
SLITJAW IMAGES (SJI)
6,000 K 15,000 K 30,000 K 65,000 K
FUV1: 1332-1358Å FUV2: 1390-1406Å
C II 1335/1336 Si IV 1394 Si IV 1403
SPECTRA
Mg II k 2796 What is IRIS?
High resolution (0.33”), far/near UV
imaging spectrograph with slit-jaw imaging
n Title
PI: Ala
Mg II h 2803
IRIS scans from the photosphere to the top of the chromosphere
courtesy Tiago Pereira
courtesy Luc Rouppe van der Voort
Very different dynamic behavior in Mg II k 2796Å: shocks and twist
Shocks (>2 min) Twist (
Effects of magneto-acoustic shocks may help explain
why TR line broadening appears to be invariant to Spatial Binning?
IRIS does not seem to resolve the non-thermal line broadening
already observed by SUMER
IRIS shows the impact of these magneto-acoustic shock waves on the TR
Mg IIh Si IV 1403Å Si IV 1403Å NTLW
λ λ x
Time
Combined λ-t plots of Mg IIh and Si IV reveal a connection of Si IV emission/broadening with
shock passage in magnetized regions
Strength of the Si IV response a function of location - increasing from CH to QS to AR
Also found in radiative MHD simulations
Spectra show evidence of rapid torsional motions and associated heating
Shocks (>2 min) Twist (
Spectra show evidence of rapid torsional motions and associated heating
See poster by Luc Rouppe van der Voort courtesy Luc
Rouppe van der Voort
Quiet Sun twist at the limb associated with
Transition Region features in Si IV
Mg II h 2803Å Dopplergram at 30 km/s Mg II h 2803Å linecenter
Si IV 1403Å intensity
courtesy Tiago Pereira
Visibility of Twist whenever line-of-sight perpendicular to magnetic fieldTwist in active regions at periphery of plage
associated with Transition Region features in Si IV
Mg II h 2803Å Dopplergram at 30 km/s Mg II h 2803Å linecenter
Si IV 1403Å intensity
courtesy Bart De Pontieu
Visibility of Twist whenever line-of-sight perpendicular to magnetic field
More ubiquitous than tornados (and different locations)Quiet Sun network shows multitude of outward propagating motions
courtesy Luc
Rouppe van der VoortImplications for chromospheric dynamics and heating?
Model chromosphere Model corona
Chromospheric/coronal heating model through turbulent 256x128x160 points
cascade of Alfven waves
64 km dx,dy
32 km dz except in corona
[van Ballegooijen et al., 2011]
•TR: yellow.
Martinez-Sykora et. al 2011
•High speed upflow: blue >45km/s
•Joule heating: green
•Hot loop (1.3MK): red
•Photospheric vertical speed: red-blue
•Magnetic field: red & blue lines
Heating & twist also observed in some numerical models of jets
Formation of spicules related to photospheric vortices?
[Kitiahsvili, 2014, see also Shelyag et al., 2011, 2014]Chromospheric spicules are heated to transition region temperatures
8,000 K 12,000 K
100,000 K 80,000 K
courtesy Tiago PereiraChromospheric spicules are heated to transition region temperatures
See poster by Tiago Pereira
courtesy Tiago Pereira
Ca II H spicules are the initial, rapid phase of violent upward motions
Followed by Mg II k and Si IV spicules which are the extensions of Ca II HHow does small-scale flux affect the atmosphere?
Magnetogram
H-alpha
Hinode/SOT movie courtesy Ted TarbellIRIS resolves so-called “unresolved
fine structure”
"
Existence hypothesized since ‘70s to
resolve coronal model discrepancies
"
Are observations dominated
by a classical TR
or
by structures unrelated to the corona?
[Feldman et al.,...]
Si IV SJI
courtesy Bart De Pontieu and Viggo HansteenThere are many low lying, short lived, cool
loops in the C II ‘1330’ and Si IV ‘1400’ slit jaw images.
“UFS” (unresolved fine structure) resolved
Si IV SJI
courtesy Viggo HansteenThese short TR loops occur naturally in rMHD sims:
high density, and thus rapid cooling: highly dynamic with strong flows
Synthetic Si IV 1403Å
Side
View
Synthetic Si IV 1403Å Dopplergram
Synthetic Si IV 1403Å
Top
View
Synthetic Si IV 1403Å Dopplergram
courtesy Viggo HansteenDiscrepancies between observations and models
of chromospheric heating
Bifrost simulation courtesy of Mats Carlsson, also available at sdc.uio.no/search/simulationsSynthetic Mg II k spectra allow detailed comparison of
numerical models with IRIS observations
Pereira et al. (2013) courtesy Tiago Pereira
Simulated Mg II k
Simulated Mg II k images with IRIS spectral resolution spectra along slit
courtesy of Tiago Pereiracourtesy of Mats Carlsson
Syntetic profiles too narrow
k2v k2R
k3
RASOLBA
HRTS
Simulation
courtesy of Tiago Pereirak3 intensity, k2 separation
courtesy of Mats CarlssonMg II k2 peak separation related to velocity gradients and column mass in chromosphere
Simulation
Observations
courtesy of Mats Carlssonk2 intensity
courtesy of Mats CarlssonMg k peak intensity
Observations
Simulation k2R k2V
courtesy of Mats CarlssonSimulations now include ion-neutral interactions
courtesy Juan Martinez-Sykora
Single-fluid MHD simulations use generalized Ohm’s law (GOL) to
include ambipolar diffusion
"
Leads to chromospheric heating, more diffuse transition region, and
denser coronaAmbipolar diffusion reduces discrepancy between
numerical models and IRIS observations
IRIS coronal hole Ambipolar Sim
No ambipolar Sim
courtesy Juan Martinez-Sykora and Tiago Pereira
Ion-neutral interactions play important role
in heating of chromosphereInclude more realistic magnetic field configuration
(e.g., canopy fields, mixed polarity fields)
courtesy of Mats CarlssonInclude more realistic magnetic field configuration
(e.g., canopy fields, mixed polarity fields)
See poster by Sydzlarski et al. courtesy of Mats Carlsson"
Higher resolution runs lead to more violent flows
Uz at z=0
courtesy of Mats Carlsson33
34
Conclusions
0. IRIS functioning well: high resolution spectra and images obtained daily
"
0. IRIS data available at: http://iris.lmsal.com/search
"
1. Chromospheric shocks have impact beyond formation of jets:
partly responsible for non-thermal line broadening of TR lines
"
2. Chromosphere is riddled with twist, associated with heating to transition
region temperatures and propagating torsional Alfven waves
"
3. Heating of chromospheric jets or spicules to transition region temperatures
"
4. Small-scale emerging flux responsible for “Unresolved fine structure” (UFS)
resolved as small-scale,~100,000 K loops?
"
5. Chromospheric heating in numerical models too weak, not enough velocity:
ion-neutral effects important?
"
6. See also talks by Paola Testa (non-thermal electrons), Patrick Antolin (IRIS evidence of
heating from resonant absorption), Hardi Peter (hot explosions), Ineke De Moortel
(propagating coronal disturbances), Lin (O I, C I formation), and posters by Pereira, Rathore,
Rouppe van der Voort,Vissers, Li, …You can also read
