UV bursts in active regions - new insights into magnetic...

UV bursts in active regions - new insights into magnetic reconnection

Dr Peter YoungGeorge Mason University, USA

NASA Goddard Space Flight Center, USA Northumbria University, UK

ISSI team Jan-2016 Mar-2017

Dr Peter Young (http://pyoung.org/talks)IRIS-8/Hinode-11

Background

Hot explosions in the cool atmosphere of the Sun

Peter et al. (2014, Science)

New active region events referred to as b*mbs due to similarities to photospheric Ellerman b*mbs

Security advice: avoid the use of the word b*mb!


What is an IRIS b*mb?Defined spectroscopically

1. Intensities of Si IV lines enhanced by factor ~1000 compared to surroundings

2. Si IV lines are broadened to 200 km s-1

3. Chromospheric absorption lines are superimposed on Si IV lines

4. Ratio of Si IV 1402.77 to O IV 1401.16 becomes much larger than in typical conditions

5. (Not related to flares)

What if we dont have a high resolution spectrometer?

[Note: linear intensity scaling]


Transition region imaging

Transition region imaging compact, intense brightenings in 1400 channel


Burst light curvesSlitjaw 1400 light curves

Bursts consist of individual spikes of duration ~ 1 minute

Can persist for 10s of minutes


Spatial morphology

Most bursts show a 1 bright point (BP)

Sometimes multiple BPs associated with same event

Jet or loop-like structures sometimes associated with

Also called flaring arch filaments (FAFs) (Vissers et al. 2015, ApJ)


Bursts generally associated with dynamic small-scale magnetic field

Burst locations from 22-Oct-2013

Magnetic field properties


Locations Moving magnetic features (MMFs)

[Gupta & Tripathi (2015, ApJ); Kim et al. (2015, ApJ)] Light bridges

[Toriumi et al. (2015, ApJ); Zhao et al. (2017, ApJ)]

Emerging flux regions [Vissers et al. (2015, ApJ); Peter et al. (2014, Science); Toriumi et al. (2017, ApJ)]


Spectroscopic signatures

Si IV 1402.8

Selection of burst profiles from 22-Oct-2013 data-set


Is there a pattern to Si IV profiles?

Note: narrow line bursts (Z. Hou. et al. 2016, ApJL)


Is there a pattern to Si IV profiles?1. Y-size is FWHM of profile in Y-direction (median value = 0.86)

2. LOS velocity and skewness derived from moments of 1D profile - generally excess of emission on blue-side of lines


Connection to Ellerman b*mbs EBs defined by H spectral signature

However, correlated with Mg II wing bursts[Tian et al. (2016, ApJ)]

About 10-20% of EBs are IBs [Tian et al. (2016, ApJ); Grubecka et al. (2016, ApJ)]

Not all IBs have an EB signature

Does EB or burst signature indicate height of reconnection in atmosphere?

J. Hong et al. (2017, ApJ)

SST/CRISP H movie (EB flames) [courtesy G. Vissers]


Types of models1D radiative transfer models

Typically add hotspot to atmosphere and perform rad. transfer[Grubecka et al. (2016, A&A), Fang et al. (2017, RAA)]

2.5D models

Model reconnection process; plasmoids, shocks [L. Ni et al. (2015, 2016); Innes et al. (2015, ApJ)]

3D MHD models with radiative transfer [next slide]


3D Modeling of emerging fluxBifrost [Hansteen et al. (2017, ApJ) - see next talk]

bursts caused by -loop reconnection at 1500 km

Problem models suggest an either/or scenario for EBs and IBs difficult to explain both signatures together

MURaM [Danilovic et al. (2017, ApJS); Danilovic (2017, A&A)] EB-only simulation EBs occur where opposite polarities come together at fast speed


FutureSolar Orbiter/SPICE

Excellent temperature coverage through transition region

DKIST Vector magnetic field evolution at high cadence and spatial resolution EB connection

Future instrumentation? Better dynamic range Faster CCD readout


Why are bursts important?

1. Fundamental reconnection event occurring in low atmosphere different plasma regime to coronal reconnection current sheet more accessible than for coronal events?

2. Space weather: do bursts give a forewarning of flares and CMEs? reconnection may be responsible for reconfiguring magnetic field [J.

Zhang & J. Wang (2002, ApJ)]


Resources

ISSI website: http://www.issibern.ch/teams/solaruvburst/

Peter Young burst website: http://pyoung.org/iris/bursts

IRIS burst publications: http://pyoung.org/iris/iris_bursts.html

IDL routines for finding bursts (Solarsoft):

IDL> iris_burst_check, filename, output=output

IDL> iris_sji_burst_check, filename, output=output

UV bursts in active regions - new insights into magnetic...

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