496 research outputs found
Phase III of USO Solar Vector Magnetograph
The Solar Vector Magnetograph (SVM) is a modern imaging spectropolarimeter
installed at Udaipur Solar Observatory (USO). Earlier phases saw the
development of the instrument using off-the-shelf components with in-house
software development. Subsequently, improvements were done in the
opto-mechanical design of the sub-systems and the telescope tracking system.
The third phase of the instrument development saw three major improvements,
these include: (i) installation of a web-camera based telescope guiding system,
developed in-house, (ii) high-cadence spectropolarimetry using Liquid Crystal
Variable Retarders and a fast CCD camera and (iii)inclusion of Na D1 line with
regular photospheric Fe 630.2 nm line for chromospheric observations.Comment: 3 pages, 1 table; To appear in the Proceedings of Evershed Meeting,
IIA, Bangalor
Estimation of width and inclination of a filament sheet using He II 304 A observations by STEREO/EUVI
The STEREO mission has been providing stereoscopic view of the filament
eruptions in EUV wavelengths. The most extended view during filament eruptions
is seen in He II 304 \AA observations, as the filament spine appears darker and
sharper. The projected filament width appears differently when viewed from
different angles by STEREO satellites. Here, we present a method for estimating
the width and inclination of the filament sheet using He II 304 \AA\
observations by STEREO-A and B satellites from the two viewpoints. The width of
the filament sheet, when measured from its feet to its apex, gives estimate of
filament height above the chromosphere.Comment: 9 pages, 2 figures, in Annales Geophysica
Organizational Control Systems and Software Quality: A Cross-National Study.
This study explores the relationship between organizational control modes (behavior, outcome, and clan) andsoftware quality. Much of the previous work on organizational control has examined the choice of modes giventask characteristics. This research extends work in control theory by considering the impact of control modeson the increasingly critical organizational outcome of software quality. The research is set in the context ofsoftware development organizations in three of the largest software developing countries: India, Ireland, andIsrael (the 3Is). A cross sectional survey of 400 software development organizations across the 3Is will be usedto test the developed model. In addition to the theoretical contributions, the study will provide practicalimplications to support software project managers in making better organizational control choices
Evidence for collapsing fields in corona and photosphere during the 15 February 2011 X2.2 flare: SDO AIA and HMI Observations
We use high-resolution images of the sun obtained by the SDO/AIA instrument
to study the evolution of the coronal loops in a flaring solar active region.
During 15 February 2011 a X-2.2 class flare occurred in NOAA 11158, a
sunspot complex. We identify three distinct phases of the
coronal loop dynamics during this event: (i) {\it Slow rise phase}: slow rising
motion of the loop-tops prior to the flare in response to slow rise of the
underlying flux rope, (ii) {\it Collapse phase}: sudden contraction of the
loop-tops with lower loops collapsing earlier than the higher loops, and (iii)
{\it Oscillation phase}: the loops exhibit global kink oscillations after the
collapse phase at different periods, with period decreasing with decreasing
height of the loops. The period of these loop oscillations is used to estimate
the field strength in the coronal loops of different loop lengths in this
active region. Further, we also use SDO/HMI observations to study the
photospheric changes close to the polarity inversion line (PIL). The
longitudinal magnetograms show step-wise permanent decrease in the magnetic
flux after the flare over a coherent patch along the PIL. Further, we examine
the HMI Stokes I,Q,U,V profiles over this patch and find that the Stokes-V
signal systematically decreases while the Stokes-Q and U signal increases after
the flare. These observations suggest that close to the PIL the field
configuration became more horizontal after the flare. We also use HMI vector
magnetic field observations to quantify the changes in the field inclination
angle and found an inward collapse of the field lines towards the polarity
inversion line (PIL) by 10. These observations are consistent
with the "coronal implosion" scenario and its predictions about flare related
photospheric field changes.Comment: 27 pages, 7 figures, in press (Astrophysical Journal
Evolution of helicity in NOAA 10923 over three consecutive solar rotations
We have studied the evolution of magnetic helicity and chirality in an active
region over three consecutive solar rotations. The region when it first
appeared was named NOAA10923 and in subsequent rotations it was numbered NOAA
10930, 10935 and 10941. We compare the chirality of these regions at
photospheric, chromospheric and coronal heights. The observations used for
photospheric and chromospheric heights are taken from Solar Vector Magnetograph
(SVM) and H_alpha imaging telescope of Udaipur Solar Observatory (USO),
respectively. We discuss the chirality of the sunspots and associated H_alpha
filaments in these regions. We find that the twistedness of superpenumbral
filaments is maintained in the photospheric transverse field vectors also. We
also compare the chirality at photospheric and chromospheric heights with the
chirality of the associated coronal loops, as observed from the HINODE X-Ray
Telescope.Comment: 8 pages, 4 figure
- …