uv bursts in active regions - new insights into magnetic ... · bifrost [hansteen et al. (2017,...

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 λ1402.77 to O IV λ1401.16 becomes much larger than in typical conditions

5. (Not related to flares)

What if we don’t have a high resolution spectrometer?

[Note: linear intensity scaling]


Transition region imaging

Transition region imaging ➡ compact, intense brightenings in 1400 Å channel


Burst light curvesSlitjaw 1400 Å light curves

• Bursts consist of individual spikes of duration ~ 1 minute

• Can persist for 10’s 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 λ1402.8

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 Ω-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 ... · bifrost [hansteen et al. (2017,...

Documents