6 research outputs found
IRIS Observations of Spicules and Structures Near the Solar Limb
We have analyzed IRIS spectral and slit-jaw observations of a quiet region
near the South Pole. In this article we present an overview of the
observations, the corrections, and the absolute calibration of the intensity.
We focus on the average profiles of strong (Mg ii h and k, C ii and Si iv), as
well as of weak spectral lines in the near ultraviolet (NUV) and the far
ultraviolet (FUV), including the Mg ii triplet, thus probing the solar
atmosphere from the low chromosphere to the transition region. We give the
radial variation of bulk spectral parameters as well as line ratios and
turbulent velocities. We present measurements of the formation height in lines
and in the NUV continuum, from which we find a linear relationship between the
position of the limb and the intensity scale height. We also find that low
forming lines, such as the Mg ii triplet, show no temporal variations above the
limb associated with spicules, suggesting that such lines are formed in a
homogeneous atmospheric layer and, possibly, that spicules are formed above the
height of 2 arc sec. We discuss the spatio-temporal structure near the limb
from images of intensity as a function of position and time. In these images,
we identify p-mode oscillations in the cores of lines formed at low heights
above the photosphere, slow moving bright features in O i and fast moving
bright features in C ii. Finally, we compare the Mg ii k and h line profiles,
together with intensity values of the Balmer lines from the literature, with
computations from the PROM57Mg non-LTE model developed at the Institut
d'Astrophysique Spatiale and estimated values of the physical parameters. We
obtain electron temperatures in the range of K at small heights to
K at large heights, electron densities from to
cm and a turbulent velocity of km/s.Comment: Accepted for publication in Solar Physic
Texture of average solar photospheric flows and the donut-like pattern
Detailed knowledge of surface dynamics is one of the key points in
understanding magnetic solar activity. The motions of the solar surface, to
which we have direct access via the observations, tell us about the interaction
between the emerging magnetic field and the turbulent fields.
The flows computed with the coherent structure tracking (CST) technique on
the whole surface of the Sun allow for the texture of the velocity modulus to
be analyzed and for one to locate the largest horizontal flows and determine
their organization. The velocity modulus maps show structures more or less
circular and closedwhich are visible at all latitudes; here they are referred
to as donuts. They reflect the most active convective cells associated with
supergranulation. These annular flows are not necessarily joined as would seem
to indicate the divergence maps. The donuts have identical properties
(amplitude, shape, inclination, etc.) regardless of their position on the Sun.
The kinematic simulation of the donuts' outflow applied to passive scalar
(corks) indicates the preponderant action of the selected donuts which are,
from our analysis, one of the major actors for the magnetic field diffusion on
the quiet Sun. The absence of donuts in the magnetized areas (plages) indicates
the action of the magnetic field on the strongest supergranular flows and thus
modifies the diffusion of the magnetic field in that location. The detection of
the donuts is a way to locate in the quiet Sun the vortex and the link with the
jet, blinkers, coronal bright points (campfires), or other physical structures.
Likewise, the study of the influence of donuts on the evolution of active
events, such as the destruction of sunspots, filament eruptions, and their
influences on upper layers via spicules and jets, could be done more
efficiently via the detection of that structures.Comment: 14 pages, 17 figure
Toulouse 2D numerical radiative transfer codes
Tutorial (5 p.); see also https://idoc.ias.u-psud.fr/MEDOC/Radiative%20transfer%20codes/MALI-GS-2DA tutorial associated with the distribution of 2D non-LTE multilevel atom radiative transfer codes