181 research outputs found
Radiative emission of solar features in Ca II K
We investigated the radiative emission of different types of solar features
in the spectral range of the Ca II K line.
We analyzed full-disk 2k x 2k observations from the PSPT Precision Solar
Photometric Telescope. The data were obtained by using three narrow-band
interference filters that sample the Ca II K line with different pass bands.
Two filters are centered in the line core, the other in the red wing of the
line. We measured the intensity and contrast of various solar features,
specifically quiet Sun (inter-network), network, enhanced network, plage, and
bright plage (facula) regions. Moreover, we compared the results obtained with
those derived from the numerical synthesis performed for the three PSPT filters
with a widely used radiative code on a set of reference semi-empirical
atmosphere models.Comment: In Proceedings of the 25th NSO Workshop: Chromospheric Structure and
Dynamic
Evolution of solar granulation fields from THEMIS-IPM time series
The temporal evolution of solar granulation has been investigated using a time series of high spatial and spectral resolution images acquired at the THEMIS solar telescope (Observatorio del Teide, Tenerife) using the IPM observing mode. In order to investigate different physical properties of solar granulation (associated horizontal velocity fields, lifetimes, intensity and geometry evolution), we identify and track solar granules automatically. We discuss the obtained results and compare them with results reported inthe literature. In order to overcome problems of atmospheric distortions, we also implement a FORTRAN95 code for the application of the Phase Diversity technique that is planned to be used at the
THEMIS telescope
Radiative emission of solar features in the Ca II K line: comparison of measurements and models
We study the radiative emission of various types of solar features, such as
quiet Sun, enhanced network, plage, and bright plage regions, identified on
filtergrams taken in the Ca II K line. We analysed fulldisk images obtained
with the PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative emission
of disk features on the filter bandpass. We also performed a NLTE spectral
synthesis of the Ca II K line integrated over the bandpass of PSPT filters. The
synthesis was carried out by utilizing both the PRD and CRD with the most
recent set of semi empirical atmosphere models in the literature and some
earlier atmosphere models. We measured the CLV of intensity values for various
solar features identified on PSPT images and compared the results obtained with
those derived from the synthesis. We find that CRD calculations derived using
the most recent quiet Sun model, on average, reproduce the measured values of
the quiet Sun regions slightly more accurately than PRD computations with the
same model. This may reflect that the utilized atmospheric model was computed
assuming CRD. Calculations with PRD on earlier quiet Sun model atmospheres
reproduce measured quantities with a similar accuracy as to that achieved here
by applying CRD to the recent model. We also find that the median contrast
values measured for most of the identified bright features, disk positions, and
filter widths are, on average, a factor 1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The discrepancy
between measured and modeled values decreases by 12% after taking into account
straylight effects on PSPT images. PRD computations on either the most recent
or the earlier atmosphere models of bright features reproduce measurements from
plage and bright plage regions with a similar accuracy.Comment: 14 pages, 18 figures, accepted by A&
Total solar irradiance during the last five centuries
The total solar irradiance (TSI) varies on timescales of minutes to centuries. On short timescales it varies due to the superposition of intensity fluctuations produced by turbulent convection and acoustic oscillations. On longer timescales, it changes due to photospheric magnetic activity, mainly because of the facular brightenings and dimmings caused by sunspots. While modern TSI variations have been monitored from space since the 1970s, TSI variations over much longer periods can only be estimated either using historical observations of magnetic features, possibly supported by flux transport models, or from the measurements of the cosmogenic isotope (e.g., 14C or 10Be) concentrations in tree rings and ice cores. The reconstruction of the TSI in the last few centuries, particularly in the 17th/18th centuries during the Maunder minimum, is of primary importance for studying climatic effects. To separate the temporal components of the irradiance variations, specifically the magnetic cycle from secular variability, we decomposed the signals associated with historical observations of magnetic features and the solar modulation potential Φ by applying an empirical mode decomposition algorithm. Thus, the reconstruction is empirical and does not require any feature contrast or field transport model. The assessed difference between the mean value during the Maunder minimum and the present value is ≃2.5 W m−2. Moreover it shows, in the first half of the last century, a growth of ≃1.5 W m−2, which stops around the middle of the century to remain constant for the next 50 years, apart from the modulation due to the solar cycle
Kinematics and Magnetic Properties of a Light Bridge in a Decaying Sunspot
We present the results obtained by analyzing high spatial and spectral
resolution data of the solar photosphere acquired by the CRisp Imaging
SpectroPolarimeter at the Swedish Solar Telescope on 6 August 2011, relevant to
a large sunspot with a light bridge (LB) observed in NOAA AR 11263. These data
are complemented by simultaneous Hinode Spectropolarimeter (SP) observation in
the Fe I 630.15 nm and 630.25 nm lines. The continuum intensity map shows a
discontinuity of the radial distribution of the penumbral filaments in
correspondence with the LB, which shows a dark lane (about 0.3" wide and about
8.0" long) along its main axis. The available data were inverted with the
Stokes Inversion based on Response functions (SIR) code and physical parameters
maps were obtained. The line-of-sight (LOS) velocity of the plasma along the LB
derived from the Doppler effect shows motions towards and away from the
observer up to 0.6 km/s, which are lower in value than the LOS velocities
observed in the neighbouring penumbral filaments. The noteworthy result is that
we find motions toward the observer up to 0.6 km/s in the dark lane where the
LB is located between two umbral cores, while the LOS velocity motion toward
the observer is strongly reduced where the LB is located between an umbral core
at one side and penumbral filaments on the other side. Statistically, the LOS
velocities correspond to upflows/downflows andcomparing these results with
Hinode/SP data, we conclude that the surrounding magnetic field configuration
(whether more or less inclined) could have a role in maintaining the conditions
for the process of plasma piling up along the dark lane. The results obtained
from our study support and confirm outcomes of recent magnetohydro-dynamic
simulations showing upflows along the main axis of a LBs
Polarised kink waves in magnetic elements: evidence for chromospheric helical waves
In recent years, new high spatial resolution observations of the Sun's atmosphere have revealed the presence of a plethora of small-scale magnetic elements down to the resolution limit of the current cohort of solar telescopes (~100–120 km on the solar photosphere). These small magnetic field concentrations, due to the granular buffeting, can support and guide several magnetohydrodynamic wave modes that would eventually contribute to the energy budget of the upper layers of the atmosphere. In this work, exploiting the high spatial and temporal resolution chromospheric data acquired with the Swedish 1 m Solar Telescope, and applying the empirical mode decomposition technique to the tracking of the solar magnetic features, we analyze the perturbations of the horizontal velocity vector of a set of chromospheric magnetic elements. We find observational evidence that suggests a phase relation between the two components of the velocity vector itself, resulting in its helical motion
Magnetic evolution of superactive regions. Complexity and potentially unstable magnetic discontinuities
In this work, we have studied the temporal evolution of some properties of a
sample of superactive regions with the aim to single out the most significant
for flare activity forecasting. We have investigated properties of 14
superactive regions, observed between January 1st 2000 and December 31st 2006
with MDI/SOHO instrument and characterized by a particularly intense flare
activity during their passage on the solar disk. We have analyzed the temporal
evolution of fractal and multifractal properties of photospheric magnetic
fields, namely the generalized fractal dimension and the cntribution and
dimensionality diversities, as well as the potential unstable volumes of
magnetic discontinuities above the studied ARs. Correlations of these
quantities with the flare index, which provides information about the flare
activity of a region, have also been estimated. We found that in 50 % of our
sample the generalized fractal dimension is correlated with the flare index
computed over windows of 50 hours, while the contribution diversity and the
dimensional diversity are anticorrelated with the same index. An increase of
the potential unstable volume of magnetic discontinuities in the corona is
observed before the phases characterized by more frequent and intense flares.
We also found that the free energy distribution functions of unstable volumes
of the analyzed superactive regions can be fitted with straight lines whose
slope is larger than the values found in previous works for less active
magnetic regions. The generalized fractal dimension and the potential unstable
volume of magnetic discontinuities are the most suitable for statistical
investigations of relations with flare activity over longer (50 hours) and
shorter (few hours) time intervals, respectively
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