1National Solar Observatory, USA; 2Stanford University ...
Transcript of 1National Solar Observatory, USA; 2Stanford University ...
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