Sushanta C. Tripathy1, K. Jain1, I. González Hernández1, R. Komm1, F. Hill1, S. McManus1, R. Bogart2, M. C. Rabello-Soares2, S. Basu3, C. Baldner3, D. A. Haber4 and B. Ravindra5

1National Solar Observatory, USA; 2Stanford University, USA; 3Yale University, USA;4University of Colorado, USA; 5Indian Institute of Astrophysics, India

This work utilizes data obtained by the Global Oscillation Network Group (GONG) program, managed by the National Solar Observatory, which is operated by AURA, Inc. under acooperative agreement with the National Science Foundation. The data were acquired by instruments operated by the Big Bear Solar Observatory, High Altitude Observatory, LearmonthSolar Observatory, Udaipur Solar Observatory, Instituto de Astrofísica de Canarias, and Cerro Tololo Interamerican Observatory. SDO data courtesy SDO (NASA) and HMI consortium.

Figure 1: HMI images

showing the 15°x15° regions

covered in this analysis for

two different days;

2010_0811_03:45 (upper

panels) and 2010_0813_13:45

(bottom panels). It is

interesting to note that the

sunspot fragments into two

separate sunspots on Aug

13, 2010. However, it is

important to note that the

regions analyzed by the ring-

diagram method are much

larger than the sunspot. Thus,

most oscillation signals are

from the plage and quiet

region surrounding the

sunspot. We further note

that the sunspot is clearly

visible in Dopplergrams.

Figure 3: Comparison of (Left) x- and (Right) y- components of horizontal flows obtained from the

inversion of HMI (blue) and GONG (red) data for two days as shown at the top of each panel. The

results are more or less consistent within 1σ errors.

Figure 5: Similar to Figure 4 but for the GONG data. The flow pattern is

similar to that noticed for the HMI data. The Ux shows a higher value for Aug 13.

The 1σ error bars are shown only at selected depths.

Figure 2: (Left) Comparison between the modes fit using HMI (blue) and GONG (red) observations of

Aug 12, 2010. (Right) The inverted sound speed profile between the active region and the quiet Sun.

For the inversion, both the regions are tracked at Carrington rotation rate for a period of 3 days (Aug 9

-11) yielding a frequency resolution of 3.86 μHz. The preliminary inversion result is similar to those

obtained for other active regions using MDI data.

MOTIVATION: With the availability of high-cadence and high-resolution Doppler and intensity images from the Helioseismic Magnetic

Imager (HMI), we investigate the sub-surface structure and dynamics of a sunspot in active region (AR) NOAA 10093. This AR is one of the

major active regions recorded during the initial observational phase of the SDO/HMI. We study the evolution of the AR during its disk

passage from August 6 to 14, 2010 using a technique of local helioseismology. We also apply the local correlation tracking method to both

Dopplergrams and continuum images to study the surface flow patterns.

Figure 4: Variation of x- and y- components of the horizontal velocity for 5

different days using HMI data as marked in the left panel. We notice that the

Ux is higher on Aug 13, when the sunspot separates into two different spots,

compared to previous days. The variation in Uy is not significant. The 1σ error

bars are only shown at selected depths.

Dopplergram Magnetogram Continuum

Ring-diagram Analysis and Sub-surface Dynamics

Local Correlation Tracking (LCT) and Surface Flows

Velocity Continuum Figure 6: The horizontal flow

field vectors at the solar

photosphere inferred using LCT.

The flows are calculated

between HMI images

separated by 5 minutes and

then averaged over a period of

45 minutes to visualize the

steady flow pattern rather than

the instantaneous changes in

the flow. We notice outflows

from the sunspots. Interestingly,

at the location where the

sunspot segregates into two

separate parts, we also note a

flow aligned with the line of

separation. The flow pattern

obtained from Dopplergrams

and continuum images are

consistent; however a

difference is noticed in the

magnitude of flows.

SUMMARY:

• The analysis suggests that there is a change in the flow pattern before

the sunspot separates into two.

• The preliminary sound speed profile obtained from the inversion

technique appears to be consistent with earlier results involving sunspots

in active regions.

• Although the HMI and GONG instruments use two different spectral lines

and hence represent values at two different heights, the inferred flow

patterns with depth are more or less similar.

• The LCT method shows the presence of a surface flow pattern aligned

with the line of separation of the fragmented sunspot.

• We use the GONG ring-diagram pipeline, tailored for the HMI data, to obtain the mode parameters

and subsurface flows.

• This technique studies high-ℓ degree waves propagating in localized areas over the solar surface toobtain an averaged velocity vector for that particular region. The selected active region consisting of

the sunspot covers an area of ~16º x 16º (384 x 384 pixels2 for HMI) that were remapped and tracked

at Snodgrass rate for 1440 min. The regions are apodized onto 15º diameter areas, and a FFT is applied

to each region on both spatial and temporal directions to obtain a 3D power spectrum. We fit the

corresponding power spectrum using a Lorentzian profile model that includes the perturbation term

due to horizontal flow fields in the region. Finally, the obtained velocities are inverted to obtain the

depth dependence of the horizontal velocity flows.

• In conjunction with HMI Dopplergrams, we also use the GONG Dopplergrams for the same period to

check for consistency.

• We also calculate the parameters corresponding to a quiet region at the same latitude but

different heliographic longitude on Aug 12, 2010.

Vt = 0.3 km/s

SH11-A-1603