Coronal Loop Oscillations Seen in Unprecedented Detail by

SDO/AIA

Rebecca White and Erwin Verwichte

University of Warwick, Centre for Fusion, Space and Astrophysics, Coventry, CV4 7AL

R.S.White@warwick.ac.uk

BUKS 2011

28th June 2011

Introduction

• Coronal loop oscillations are interpreted as the fast kink mode.

• Observations of coronal loop oscillations since 1998, majority with TRACE e.g.

- Nakariakov et al 1999

- Aschwanden et al 1999

- Verwichte et al 2004, 2010

- Van Doorsselaere et al 2007

• Launch of SDO in 2010 carrying the Atmospheric Imaging Assembly (AIA) instrument.

- 7 EUV band passes (94Å - 335 Å)

- Continuous full disk images

- Spatial resolution 1.5″, time cadence ~ 12s

Motivation:

• Study multiple loops in the same event.

• Combine AIA/SDO data with EUVI/STEREO data to obtain the 3D

loop geometry.

• The short time cadence of AIA may allow shorter period oscillations to

be observed.

• Application of seismology techniques to the fast kink mode:

- Used to probe local properties of the coronal plasma

such as the magnetic field.

Introduction

• 3 events studied in the 171Å bandpass • Oscillations triggered by a flare/CME event.

• 11 loops studied• 3D information using STEREO obtained for 6 loops

Observations

M1.0 GOES flare C4.9 GOES flare

13 June 2010

02 August 2010

03 November 2010

Time Series Analysis

• Cuts made perpendicular to the loops.

• Loop features enhanced by applying a 2D wavelet transform.

• Gaussian plus background profile fitted to the flux at each time to attempt to automatically locate the loop position.

• Damped cosine function fitted to the resulting time series after background subtraction:

Time Series Analysis

Intensity Oscillations• Intensity obtained from the cuts using

the time series points.

• Reliably observed for 6 loops.

• Possible explanation of intensity variations:

– Variations of line of sight column depth. Verwichte et al. (2009)

– Vertically polarised mode. Wang and Solanki (2004)

– Non linear coupling of the kink mode to a slow magnetoacoustic mode. Terradas and Ofman (2004)

– Linear coupling of the kink mode to a slow magnetoacoustic mode. Terradas et al. (2011)

2 3 4 5

Intensity Oscillations

Intensity amplitude increases with displacement amplitude for this loop.

→ Consistent with l.o.s variations.

2 3

54

3D Loop Geometry from STEREO

Azimuth = 68.8° Inclination = 26.0°

ResultsEvent 1 (13 June 2010):

Intensity oscillations:

• Periods between 3.55 minutes and 3.75 minutes for displacement time series.

• Periods of 3.58 minutes and 4.12 minutes for intensity oscillations.

ResultsEvent 2 (02 August 2010):

Intensity oscillations:

• Periods of 8.67 minutes and 9.93 minutes for displacement time series.

• Periods of 9.17 minutes and 10.2 minutes for intensity oscillations.

ResultsEvent 3 (03 November 2010):

• Period scales with loop length and possibly footpoint distance from the event.

• Periods of less than 2 minutes found for loops 4 and 5.

Intensity oscillations:

Results

DEM Analysis

• Differential emission measure distribution analysis

technique. Aschwanden, (2011)

• First estimate of the average magnetic field strength

made by estimating the density contrast in the 171Å

bandpass:

B = 16.72 ± 3.34 G

Conclusions and Future Work

• Performed the analysis of 11 coronal loop oscillations, determining periods,

damping times and phases.

- 3D geometry obtained for 6 loops using EUVI/STEREO.

- DEM analysis to be applied to suitable loops.

• Oscillations with periods of less than 2 minutes observed.

• Intensity oscillations reliably observed in 6 of the loops.

- Most likely due to line of sight effect but other possibilities cannot

be ruled out.

• Seismology techniques are to be applied to the kink mode e.g Goossens et

al 2008, Nakariakov and Ofman 2001.