Submerged Acoustic Sources�

The 

SOL20140207T10:28

Study Case

SPHERE 2022 ECR Talks – Boulder, CO

Savannah Perez-Piel¹, Juan Camilo Buitrago-Casas¹, Juan Carlos Martínez Oliveros¹, Charles Lindsey²

¹Space Sciences Laboratory - University of California Berkeley ⦁ ²NorthWest Research Associates

Contents

• Overview of Sunquakes and Acoustic Sources� 
• The Study of SOL20140207T10:28�
• Application of New Visualization Methods�
• Conclusions and Future Work

� Sunquakes & Acoustic Sources

Sunquakes & Acoustic Sources

• Sunquakes are a manifestation of seismic transients released into the solar interior and refer to the observed helioseismic signatures.�
• When the transient refracts back upwards, the generated tremors are considered the sunquake.

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• Current belief is that some solar flares are the sole generation for the seismic waves. It is thought that he energy from the flare’s impulsive phase drives the acoustic transient into the subphotosphere.

Sunquakes & Acoustic Sources

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• Sources refer to the compact sources of acoustic power that can be triggered.�
• Many compact sources can be recognized in any given flare. A submerged source refers to one of these acoustic power sources that is suspended at some depth below the photosphere. 

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SOL20140207T10:28

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• This flare is one of a set of 18 flares compiled by Buitrago-Casas et al. (2015), all occurring in solar cycle 24.
• It is the only flare in the set to show evidence of a submerged source.
• Date: February 7^th, 2014 
• Class: M1.9-class flare
• Region: NOAA-AR 11968
• Magnetic Classification: beta-gamma configuration (referring to a bipolar group with a complex division of polarity).  
• It reached maximum EUV (He II 304 ̊A) irradiance at five minutes post-onset.
• It fades to relative EUV obscurity about 30 minutes thereafter.

AIA 1700

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The Sun in EUV (He II 304  ̊A)

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Two minutes pre-flare.

Flare Profiles

NOAA AR11968

GOES

X-Ray

AIA�1700

Photosphere

Egression

10mHz

FLUX

Evidence of a Submerged Source

• A sequence of acoustic source density maps where the focal plane is submerged. The seismic signature spreads spatially outward and becomes diffuse (Focusing).�
• The source is most compact at 2230 km.

Quiet Photosphere

Sub-photosphere

Evidence of a Submerged Source

Preflare line-of-sight magnetic induction 

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Mean-square amplitude of local acoustic oscillations in the 9–11-mHz spectral band during the impulsive phase 

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Preflare continuum intensity

EUV intensity in the line He II λ304 ̊A during the impulsive

phase of the flare.

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Map of acoustic source density in the 9–11-mHz band during the impulsive phase of the flare focused at the base of the quiet photosphere

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Map of acoustic source density in the 5–7-mHz band during the impulsive phase of the flare focused at the base of the quiet photosphere

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Evidence of a Submerged Source

• Source Density images of 6, 8, and 10 mHz in relation to the site of strong local acoustic power of 10 mHz oscillations.�
• Upper left and lower left images are taken at the surface of photosphere.�
• Blue circles mark the horizontal location of the 10-mHz submerged source in each frame.

Visualization Methods�Time-Depth and Temporal Maps 

New Visualization Method

• For a given frequency and radius in pixels we have created a new method to easily visualize depths and intensities to better pinpoint potential submerged sources. 

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• These are 2D representations of the intensity within a  marked region of radius, R in pixels during an impulsive event at depths of up to 2.8 Mm.  The X-Axis corresponds to the UTC time of the event, and the Y-Axis represents the depths of the sub-photospheric  layer. 

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• A line can be fit to the primary “comet trail” of the event and give a reasonable result for the sound speed within the solar medium.

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• We applied computational helioseismic holographic techniques to probe the subphotospheric layer. Hologram refers to the numerical calculation of each pixel of the oscillation at the wavefront.�
• The catalog is based on the RHESSI flare catalog and therefore each flare was detected in HXR. The flares show observable enhanced continuum emission, and doppler transients.�
• From Acoustic Power Maps (Egression), we create the Time-Depths and Temporal Plot

A mask is applied to filter out acoustic power in the spectral domain, the map is then transformed back to the spatial domain, generating the acoustic egression map.

New Visualization Method

The Acoustic Power Map is created by integrating the acoustic egression over the relevant time interval at a single depth.

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Surface Source

Submerged Source

New Visualization Method

At Base of the Photosphere

Surface Source

Submerged Source

At Base of the Photosphere

New Visualization Method

Surface Source

Submerged Source

New Visualization Method

At Base of the Photosphere

New Visualization Method

Results

Conclusions & Future Work

• We can see a 10 mHz source in the time-depth maps ahead of the onset of the flare. It is at a depth 1.5Mm + below the photosphere. It is predominant over the overlying surface sources as described in Lindsey et al 2020.
• As we find evidence of a submerged source triggered before those surface events.
• Paradigm states that flares create the surface sunquakes. We propose perhaps a different – yet unknown -mechanism is at play triggering these events.

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Conclusions & Future Work

• Future Work includes:
• Looking for ways this went wrong!
• better fitting radius
• taking into account overlapping and possible interacting sources

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• Looking for more examples
• Finding more sunquakes with submerged sources
• Expanding the data sources we use

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Thank you for your attention! 

Any questions?

savannah_sky@berkeley.edu

savssolarscience.com

Backup Slides

New Visualization Method – �Submerged Source

New Visualization Method – �Surface Source

New Visualization Method – �Surface Source

New Visualization Method – �Submerged Source