2,382 research outputs found
Oscillations above sunspots from the temperature minimum to the corona
Context. An analysis of the oscillations above sunspots was carried out using
simultaneous ground-based and Solar Dynamics Observatory (SDO) observations
(SiI 10827A, HeI 10830A, FeI 6173A, 1700A, HeII 304A, FeIX 171A).
Aims. Investigation of the spatial distribution of oscillation power in the
frequency range 1-8 mHz for the different height levels of the solar
atmosphere. Measuring the time lags between the oscillations at the different
layers.
Methods. We used frequency filtration of the intensity and Doppler velocity
variations with Morlet wavelet to trace the wave propagation from the
photosphere to the chromosphere and the corona.
Results. The 15 min oscillations are concentrated near the outer penumbra in
the upper photosphere (1700 A), forming a ring, that expands in the transition
zone. These oscillations propagate upward and reach the corona level, where
their spatial distribution resembles a fan structure. The spatial distribution
of the 5 min oscillation power looks like a circle-shape structure matching the
sunspot umbra border at the photospheric level. The circle expands at the
higher levels (HeII 304A and FeIX 171A). This indicates that the low-frequency
oscillations propagate along the inclined magnetic tubes in the spot. We found
that the inclination of the tubes reaches 50--60 degrees in the upper
chromosphere and the transition zone. The main oscillation power in the 5-8 mHz
range concentrates within the umbra boundaries at all the levels. The highest
frequency oscillations (8 mHz) are located in the peculiar points inside the
umbra. These points probably coincide with umbral dots. We deduced the
propagation velocities to be 28+-15 km/s, 26+-15 km/s, and 55+-10 km/s for the
SiI 10827A-HeI 10830A, 1700A-HeII 304A, and HeII 304A-FeIX 171A height levels,
respectively
Features of spatial distribution of oscillations in faculae regions
We found that oscillations of LOS velocity in H-alpha are different for
various parts of faculae regions. Power spectra show that the contribution of
low-frequency modes (1.2 - 2 mHz) increase at the network boundaries. Three and
five- minute periods dominate inside cells. The spectra of photosphere and
chromosphere LOS velocity oscillations differ for most faculae. On the other
hand, we detected several cases where propagating oscillations in faculae were
manifest with a five-minute period. Their initiation point on spatial-temporal
diagrams coincided with the local maximum of the longitudinal magnetic field.Comment: 6 pages, 4 figure
Magneto-acoustic wave energy from numerical simulations of an observed sunspot umbra
We aim at reproducing the height dependence of sunspot wave signatures
obtained from spectropolarimetric observations through 3D MHD numerical
simulations. A magneto-static sunspot model based on the properties of the
observed sunspot is constructed and perturbed at the photosphere introducing
the fluctuations measured with the \SiI\ 10827 \AA\ line. The results
of the simulations are compared with the oscillations observed simultaneously
at different heights from the \HeI\ 10830 \AA\ line, the \CaIIH\ core
and the \FeI\ blends in the wings of the \CaIIH\ line. The simulations show a
remarkable agreement with the observations. They reproduce the velocity maps
and power spectra at the formation heights of the observed lines, as well as
the phase and amplification spectra between several pair of lines. We find that
the stronger shocks at the chromosphere are accompanied with a delay between
the observed signal and the simulated one at the corresponding height,
indicating that shocks shift the formation height of the chromospheric lines to
higher layers. Since the simulated wave propagation matches very well the
properties of the observed one, we are able to use the numerical calculations
to quantify the energy contribution of the magneto-acoustic waves to the
chromospheric heating in sunspots. Our findings indicate that the energy
supplied by these waves is too low to balance the chromospheric radiative
losses. The energy contained at the formation height of the lowermost \SiI\
10827 \AA\ line in the form of slow magneto-acoustic waves is already
insufficient to heat the higher layers, and the acoustic energy which reaches
the chromosphere is around 3-9 times lower than the required amount of energy.
The contribution of the magnetic energy is even lower.Comment: Accepted for publication in The Astrophysical Journa
Relativistic model of hidden bottom tetraquarks
The relativistic model of the ground state and excited heavy tetraquarks with
hidden bottom is formulated within the diquark-antidiquark picture. The diquark
structure is taken into account by calculating the diquark-gluon vertex in
terms of the diquark wave functions. Predictions for the masses of bottom
counterparts to the charm tetraquark candidates are given.Comment: 6 page
Changes in Job Structure and Rising Wage Inequality in Urban China, 1995-2007
We use household surveys from 1995, 2002, and 2007 to examine how changes in job structure contributed to China's rising urban wage inequality, considering three job characteristics: occupation, industry, and firm ownership. The explanatory power of job structure for wage inequality increased between 1995 and 2007. Both the change in relative number of jobs (composition effect) and the change in between-job and within-job wage gaps (price effect) contributed to rising wage inequality. Price effect was the major contributor, whereas composition effect played a larger role in the 1995-2002 period than in the 2002-2007 period, and at the lower-half distribution. Between-job inequality played a major role in the first period, and within-job inequality played a major role in the second period. Our results suggest that both technological change and institutional features influence job structure and wage inequality.job structure, wage inequality, urban China, decomposition
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