49 research outputs found
Local helioseismology of sunspot regions: comparison of ring-diagram and time-distance results
Local helioseismology provides unique information about the subsurface
structure and dynamics of sunspots and active regions. However, because of
complexity of sunspot regions local helioseismology diagnostics require careful
analysis of systematic uncertainties and physical interpretation of the
inversion results. We present new results of comparison of the ring-diagram
analysis and time-distance helioseismology for active region NOAA 9787, for
which a previous comparison showed significant differences in the subsurface
sound-speed structure, and discuss systematic uncertainties of the measurements
and inversions. Our results show that both the ring-diagram and time-distance
techniques give qualitatively similar results, revealing a characteristic
two-layer seismic sound-speed structure consistent with the results for other
active regions. However, a quantitative comparison of the inversion results is
not straightforward. It must take into account differences in the sensitivity,
spatial resolution and the averaging kernels. In particular, because of the
acoustic power suppression, the contribution of the sunspot seismic structure
to the ring-diagram signal can be substantially reduced. We show that taking
into account this effect reduces the difference in the depth of transition
between the negative and positive sound-speed variations inferred by these
methods. Further detailed analysis of the sensitivity, resolution and averaging
properties of the local helioseismology methods is necessary for consolidation
of the inversion results. It seems to be important that both methods indicate
that the seismic structure of sunspots is rather deep and extends to at least
20 Mm below the surface, putting constraints on theoretical models of sunspots.Comment: 10 pages, 10 figures, submitted to Journal of Physics: Conference
Series (JPCS) GONG 2010 - SoHO 24 "A new era of seismology of the Sun and
solar-like stars", June 27 - July 2, 2010 Aix-en-Provence, Franc
Subsurface Meridional Circulation in the Active Belts
Temporal variations of the subsurface meridional flow with the solar cycle
have been reported by several authors. The measurements are typically averaged
over periods of time during which surface magnetic activity existed in the
regions were the velocities are calculated. The present work examines the
possible contamination of these measurements due to the extra velocity fields
associated with active regions plus the uncertainties in the data obtained
where strong magnetic fields are present. We perform a systematic analysis of
more than five years of GONG data and compare meridional flows obtained by
ring-diagram analysis before and after removing the areas of strong magnetic
field. The overall trend of increased amplitude of the meridional flow towards
solar minimum remains after removal of large areas associated with surface
activity. We also find residual circulation toward the active belts that
persist even after the removal of the surface magnetic activity, suggesting the
existence of a global pattern or longitudinally-located organized flows.Comment: 12 pages, 6 figures, Submitted to Solar Physics. Accepted
(08/25/2008
The Multiview Observatory for Solar Terrestrial Science (MOST)
We report on a study of the Multiview Observatory for Solar Terrestrial
Science (MOST) mission that will provide comprehensive imagery and time series
data needed to understand the magnetic connection between the solar interior
and the solar atmosphere/inner heliosphere. MOST will build upon the successes
of SOHO and STEREO missions with new views of the Sun and enhanced instrument
capabilities. This article is based on a study conducted at NASA Goddard Space
Flight Center that determined the required instrument refinement, spacecraft
accommodation, launch configuration, and flight dynamics for mission success.
MOST is envisioned as the next generation great observatory positioned to
obtain three-dimensional information of large-scale heliospheric structures
such as coronal mass ejections, stream interaction regions, and the solar wind
itself. The MOST mission consists of 2 pairs of spacecraft located in the
vicinity of Sun-Earth Lagrange points L4 (MOST1, MOST3) and L5 (MOST2 and
MOST4). The spacecraft stationed at L4 (MOST1) and L5 (MOST2) will each carry
seven remote-sensing and three in-situ instrument suites. MOST will also carry
a novel radio package known as the Faraday Effect Tracker of Coronal and
Heliospheric structures (FETCH). FETCH will have polarized radio transmitters
and receivers on all four spacecraft to measure the magnetic content of solar
wind structures propagating from the Sun to Earth using the Faraday rotation
technique. The MOST mission will be able to sample the magnetized plasma
throughout the Sun-Earth connected space during the mission lifetime over a
solar cycle.Comment: 42 pages, 19 figures, 8 tables, to appear in J. Atmospheric and Solar
Terrestrial Physic
Lifetimes of High-Degree p Modes in the Quiet and Active Sun
We study variations of the lifetimes of high-degree solar p-modes in the
quiet and active Sun with the solar activity cycle. The lifetimes in the degree
range 300 - 600 and frequency 2.5 - 4.5 mHz were computed from SOHO/MDI data in
an area including active regions and quiet Sun using the time-distance
technique. We applied our analysis to the data in four different phases of
solar activity: in 1996 (at minimum), 1998 (rising phase), 2000 (at maximum)
and 2003 (declining phase). The results from the area with active regions show
that the lifetime decreases as activity increases. The maximal lifetime
variations are between solar minimum in 1996 and maximum in 2000; the relative
variation averaged over all mode degree values and frequencies is a decrease of
about 13%. The lifetime reductions relative to 1996 are about 7% in 1998 and
about 10% in 2003. The lifetime computed in the quiet region still decreases
with solar activity although the decrease is smaller. On average, relative to
1996, the lifetime decrease is about 4% in 1998, 10% in 2000 and 8% in 2003.
Thus, measured lifetime increases when regions of high magnetic activity are
avoided. Moreover, the lifetime computed in quiet regions also shows variations
with activity cycle.Comment: 13 pages, 5 figures; Accepted for publication in Solar Physic
Small frequency separations as seen in the autocorrelation function of the whole-disk measurements
International audienc
Use of Engineering Programs in the Process of Teaching Physics
This article analyzes the problems that arise in the process of research, practical and laboratory work of students in physics, as well as the advantages and solutions of these problems using virtual software, and the possibility of performing practical and laboratory work using Multisim. and information on methods