76 research outputs found
Relation between trees of fragmenting granules and supergranulation evolution
Context: The determination of the underlying mechanisms of the magnetic
elements diffusion over the solar surface is still a challenge. Understanding
the formation and evolution of the solar network (NE) is a challenge, because
it provides a magnetic flux over the solar surface comparable to the flux of
active regions at solar maximum. Aims: We investigate the structure and
evolution of interior cells of solar supergranulation. From Hinode
observations, we explore the motions on solar surface at high spatial and
temporal resolution. We derive the main organization of the flows inside
supergranules and their effect on the magnetic elements. Method: To probe the
superganule interior cell, we used the Trees of Fragmenting Granules (TFG)
evolution and their relations to horizontal Results: Evolution of TFG and their
mutual interactions result in cumulative effects able to build horizontal
coherent flows with longer lifetime than granulation (1 to 2 hours) over a
scale up to 12\arcsec. These flows clearly act on the diffusion of the
intranetwork (IN) magnetic elements and also on the location and shape of the
network. Conclusions: From our analysis during 24 hours, TFG appear as one of
the major elements of the supergranules which diffuse and advect the magnetic
field on the Sun's surface. The strongest supergranules contribute the most to
magnetic flux diffusion in the solar photosphere.Comment: 13 pages, 17 figures, accepted in Astronomy and Astrophysics movie :
http://www.lesia.obspm.fr/perso/jean-marie-malherbe/Hinode2007/hinode2007.htm
Polar cap magnetic field reversals during solar grand minima: could pores play a role?
We study the magnetic flux carried by pores located outside active regions
with sunspots and investigate their possible contribution to the reversal of
the global magnetic field of the Sun. We find that they contain a total flux of
comparable amplitude to the total magnetic flux contained in polar caps. The
pores located at distances of 40--100~Mm from the closest active region have
systematically the correct sign to contribute to the polar cap reversal. These
pores can predominantly be found in bipolar magnetic regions. We propose that
during grand minima of solar activity, such a systematic polarity trend, akin
to a weak magnetic (Babcock-Leighton-like) source term could still be operating
but was missed by the contemporary observers due to the limited resolving power
of their telescopes.Comment: 11 pages, 9 figures, accepted for publication in
Astronomy&Astrophysic
Comparison of solar surface flows inferred from time--distance helioseismology and coherent structure tracking using HMI/SDO observations
We compare measurements of horizontal flows on the surface of the Sun using
helioseismic time--distance inversions and coherent structure tracking of solar
granules. Tracking provides 2D horizontal flows on the solar surface, whereas
the time--distance inversions estimate the full 3-D velocity flows in the
shallow near-surface layers. Both techniques use HMI observations as an input.
We find good correlations between the various measurements resulting from the
two techniques. Further, we find a good agreement between these measurements
and the time-averaged Doppler line-of-sight velocity, and also perform sanity
checks on the vertical flow that resulted from the 3-D time--distance
inversion.Comment: 22 pages of the manuscript, 5 figures, 3 tables, accepted for
publication in the Astrophysical Journa
On mesogranulation, network formation and supergranulation
We present arguments which show that in all likelihood mesogranulation is not
a true scale of solar convection but the combination of the effects of both
highly energetic granules, which give birth to strong positive divergences
(SPDs) among which we find exploders, and averaging effects of data processing.
The important role played by SPDs in horizontal velocity fields appears in the
spectra of these fields where the scale 4 Mm is most energetic; we
illustrate the effect of averaging with a one-dimensional toy model which shows
how two independent non-moving (but evolving) structures can be transformed
into a single moving structure when time and space resolution are degraded.
The role of SPDs in the formation of the photospheric network is shown by
computing the advection of floating corks by the granular flow. The coincidence
of the network bright points distribution and that of the corks is remarkable.
We conclude with the possibility that supergranulation is not a proper scale of
convection but the result of a large-scale instability of the granular flow,
which manifests itself through a correlation of the flows generated by SPDs.Comment: 10 pages, 11 figures, to appear in Astronomy and Astrophysic
Quasi full-disk maps of solar horizontal velocities using SDO/HMI data
For the first time, the motion of granules (solar plasma on the surface on
scales larger than 2.5 Mm) has been followed over the entire visible surface of
the Sun, using SDO/HMI white-light data.
Horizontal velocity fields are derived from image correlation tracking using
a new version of the coherent structure tracking algorithm.The spatial and
temporal resolutions of the horizontal velocity map are 2.5 Mm and 30 min
respectively .
From this reconstruction, using the multi-resolution analysis, one can obtain
to the velocity field at different scales with its derivatives such as the
horizontal divergence or the vertical component of the vorticity. The intrinsic
error on the velocity is ~0.25 km/s for a time sequence of 30 minutes and a
mesh size of 2.5 Mm.This is acceptable compared to the granule velocities,
which range between 0.3 km/s and 1.8 km/s. A high correlation between
velocities computed from Hinode and SDO/HMI has been found (85%). From the data
we derive the power spectrum of the supergranulation horizontal velocity field,
the solar differential rotation, and the meridional velocity.Comment: 8 pages, 11 figures, accepted in Astronomy and Astrophysic
Multiscale magnetic underdense regions on the solar surface: Granular and Mesogranular scales
The Sun is a non-equilibrium dissipative system subjected to an energy flow
which originates in its core. Convective overshooting motions create
temperature and velocity structures which show a temporal and spatial
evolution. As a result, photospheric structures are generally considered to be
the direct manifestation of convective plasma motions. The plasma flows on the
photosphere govern the motion of single magnetic elements. These elements are
arranged in typical patterns which are observed as a variety of multiscale
magnetic patterns. High resolution magnetograms of quiet solar surface revealed
the presence of magnetic underdense regions in the solar photosphere, commonly
called voids, which may be considered a signature of the underlying convective
structure. The analysis of such patterns paves the way for the investigation of
all turbulent convective scales from granular to global. In order to address
the question of magnetic structures driven by turbulent convection at granular
and mesogranular scales we used a "voids" detection method. The computed voids
distribution shows an exponential behavior at scales between 2 and 10 Mm and
the absence of features at 5-10 Mm mesogranular scales. The absence of
preferred scales of organization in the 2-10 Mm range supports the multiscale
nature of flows on the solar surface and the absence of a mesogranular
convective scale
Aquaporins: important but elusive drug targets.
The aquaporins (AQPs) are a family of small, integral membrane proteins that facilitate water transport across the plasma membranes of cells in response to osmotic gradients. Data from knockout mice support the involvement of AQPs in epithelial fluid secretion, cell migration, brain oedema and adipocyte metabolism, which suggests that modulation of AQP function or expression could have therapeutic potential in oedema, cancer, obesity, brain injury, glaucoma and several other conditions. Moreover, loss-of-function mutations in human AQPs cause congenital cataracts (AQP0) and nephrogenic diabetes insipidus (AQP2), and autoantibodies against AQP4 cause the autoimmune demyelinating disease neuromyelitis optica. Although some potential AQP modulators have been identified, challenges associated with the development of better modulators include the druggability of the target and the suitability of the assay methods used to identify modulators
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