Kitiashvili, I.

Kosovichev, A.

Mansour, N.

Wray, A.

English

NASA Technical Reports Server

I. Kitiashvili1, A. Kosovichev2, A. Wray1, N. Mansour1 
1NASA Ames Research Center, 2NJIT 
 
Effects of Distributed Magnetic Fields 
and Compact Magnetic Structures on 
Properties of Acoustic Waves Excitation on the Sun 
https://ntrs.nasa.gov/search.jsp?R=20200000915 2020-03-28T19:05:05+00:00Z
Magnetoacoustic waves in sunspots	
Zhao et al., 2015 Beckers & Schultz, 1972  
5Mm deep ? 
Spontaneous pore formation 
Kitiashvili et al., 2010 
Acoustic waves in vicinity compact magnetic 
structure 
Example of acoustic wave excited in vicinity of the pore-like magnetic structure shows the 
time-difference of gas pressure fluctuations in the horizontal plane (z = -1.5Mm) and vertical 
y-z slices at x = 2.36Mm. Red contours correspond to the photospheric Bz = 500G. Time-
difference between the snapshots is 30 sec. 
Acoustic wave inside the pore	
Subsurface acoustic events cause localized quasi-periodic 
gas pressure fluctuations with the period of 2 - 4 min 
Identification of wave fronts from averaged 
normalized gas pressure fluctuations 
Example of acoustic wave event excited inside the pore 2 Mm beneath the surface. The images 
show the time-difference of the normalized gas pressure fluctuations averaged in y-direction. 
Time-difference between snapshots is 30 sec. 
Time-distance diagram of the deep acoustic event 	
z = -1.2 Mm 
The ridges on the time-
distance diagram 
correspond to wave 
propagation with the 
speed of ~14 km/s. 
Statistical properties of acoustic events 
Conclusions 
•  Excitation of the acoustic waves is observed everywhere on the Sun, reflecting 
subsurface dynamics of solar magnetoconvection. Recent helioseismology 
inferences have demonstrated the possibility of acoustic wave excitation in 
subsurface layers around sunspots much deeper than 200 km.  
 
•  Using 3D radiative MHD numerical simulations, we investigated acoustic wave 
excitation in the case of distributed magnetic field and spontaneously formed, 
highly magnetized pore-like structure, and show that, in the presence of strong 
magnetic field structures, acoustic waves can indeed be excited much deeper 
than in quiet-Sun regions. 
•  The distribution of acoustic events with depth depends on the magnetic field 
scale. In particular, in the case of small-scale magnetic patches, the acoustic 
events are located in a relative shallow, 0.5-1 Mm deep layer, while acoustic 
sources located inside a self-organized pore-like magnetic structure can be 
found as deep up to 3-4 Mm below the surface. 
•  The primary mechanisms of the deep acoustic sources are deeply penetrating 
downdrafts and pressure fluctuations caused by interacting magnetic flux 
tubes. 


Effects of Distributed Magnetic Fields and Compact Magnetic Structures on Properties of Acoustic Waves Excitation on the Sun

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