21 research outputs found
Space-time segmentation method for study of the vertical structure and evolution of solar supergranulation from data provided by local helioseismology
Solar supergranulation remains a mystery in spite of decades of intensive
studies. Most of the papers about supergranulation deal with its surface
properties. Local helioseismology provides an opportunity to look below the
surface and see the vertical structure of this convective structure. We present
a concept of a (3+1)-D segmentation algorithm capable of recognising individual
supergranules in a sequence of helioseismic 3-D flow maps. As an example, we
applied this method to the state-of-the-art data and derived descriptive
statistical properties of segmented supergranules -- typical size of 20--30 Mm,
characteristic lifetime of 18.7 hours, and estimated depth of 15--20 Mm. We
present preliminary results obtained on the topic of the three-dimensional
structure and evolution of supergranulation. The method has a great potential
in analysing the better data expected from the helioseismic inversions, which
are being developed.Comment: 6 pages, 4 figures, accepted in New Astronom
Large-scale horizontal flows in the solar photosphere V: Possible evidence for the disconnection of bi-polar sunspot groups from their magnetic roots
In a recent paper (Svanda et al., 2008, A&A 477, 285) we pointed out that,
based on the tracking of Doppler features in the full-disc MDI Dopplergrams,
the active regions display two dynamically different regimes. We speculated
that this could be a manifestation of the sudden change in the active regions
dynamics, caused by the dynamic disconnection of sunspots from their magnetic
roots as proposed by Schuessler & Rempel (2005, A&A 441, 337). Here we
investigate the dynamic behaviour of the active regions recorded in the
high-cadence MDI data over the last solar cycle in order to confirm the
predictions in the Schuessler's & Rempel's paper. We find that, after drastic
reduction of the sample, which is done to avoid disturbing effects, a large
fraction of active regions displays a sudden decrease in the rotation speed,
which is compatible with the mechanism of the dynamic disconnection of sunspots
from their parental magnetic structures.Comment: 11 pages, 9 figures, 1 table; accepted in Astronomy & Astrophysic
Large-scale horizontal flows in the solar photosphere II: Long-term behaviour and magnetic activity response
Recently, we have developed a method useful for mapping large-scale
horizontal velocity fields in the solar photosphere. The method was developed,
tuned and calibrated using the synthetic data. Now, we applied the method to
the series of Michelson Doppler Imager (MDI) dopplergrams covering almost one
solar cycle in order to get the information about the long-term behaviour of
surface flows. We have found that our method clearly reproduces the widely
accepted properties of mean flow field components, such as torsional
oscillations and a pattern of meridional circulation. We also performed a
periodic analysis, however due to the data series length and large gaps we did
not detect any significant periods. The relation between the magnetic activity
influencing the mean zonal motion is studied. We found an evidence that the
emergence of compact magnetic regions locally accelerates the rotation of
supergranular pattern in their vicinity and that the presence of magnetic
fields generally decelerates the rotation in the equatorial region. Our results
show that active regions in the equatorial region emerge exhibiting a constant
velocity (faster by 60 +/- 9 m/s than Carrington rate) suggesting that they
emerge from the base of the surface radial shear at 0.95 R_sun, disconnect from
their magnetic roots, and slow down during their evolution.Comment: 9 pages, 8 figures, accepted for publication in Astronomy &
Astrophysic
Large-scale horizontal flows in the solar photosphere I: Method and tests on synthetic data
We propose a useful method for mapping large-scale velocity fields in the
solar photosphere. It is based on the local correlation tracking algorithm when
tracing supergranules in full-disc dopplergrams. The method was developed using
synthetic data. The data processing the data are transformed during the data
processing into a suitable coordinate system, the noise is removed, and finally
the velocity field is calculated. Resulting velocities are compared with the
model velocities and the calibration is done. From our results it becomes clear
that this method could be applied to full-disc dopplergrams acquired by the
Michelson Doppler Imager (MDI) onboard the Solar and Heliospheric Observatory
(SoHO).Comment: Accepted in Astronomy and Astrophycic
A retrospective of the GREGOR solar telescope in scientific literature
In this review, we look back upon the literature, which had the GREGOR solar
telescope project as its subject including science cases, telescope subsystems,
and post-focus instruments. The articles date back to the year 2000, when the
initial concepts for a new solar telescope on Tenerife were first presented at
scientific meetings. This comprehensive bibliography contains literature until
the year 2012, i.e., the final stages of commissioning and science
verification. Taking stock of the various publications in peer-reviewed
journals and conference proceedings also provides the "historical" context for
the reference articles in this special issue of Astronomische
Nachrichten/Astronomical Notes.Comment: 6 pages, 2 color figures, this is the pre-peer reviewed version of
Denker et al. 2012, Astron. Nachr. 333, 81
Large-scale horizontal flows in the solar photosphere. IV. On the vertical structure of large-scale horizontal flows
In the recent papers, we introduced a method utilised to measure the flow
field. The method is based on the tracking of supergranular structures. We did
not precisely know, whether its results represent the flow field in the
photosphere or in some sub-photospheric layers. In this paper, in combination
with helioseismic data, we are able to estimate the depths in the solar
convection envelope, where the detected large-scale flow field is well
represented by the surface measurements. We got a clear answer to question what
kind of structures we track in full-disc Dopplergrams. It seems that in the
quiet Sun regions the supergranular structures are tracked, while in the
regions with the magnetic field the structures of the magnetic field are
dominant. This observation seems obvious, because the nature of Doppler
structures is different in the magnetic regions and in the quiet Sun. We show
that the large-scale flow detected by our method represents the motion of
plasma in layers down to ~10 Mm. The supergranules may therefore be treated as
the objects carried by the underlying large-scale velocity field.Comment: 8 pages, 5 figures, accepted in New Astronom