37 research outputs found
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
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
Problems in Observation and Identification of Torsional Waves in the Lower Solar Atmosphere
Registering periodic variations of spectral line widths serves as the main
method for observing torsional Alfv\'{e}n waves. Theoretically, the method
seems valid, yet it entails a number of caveats when applied to data. For
instance, the amplitudes of these observations should vary with changes of the
location on the disk, and they should be associated with no intensity
oscillations. We analyze extensive observational material of periodic
non-thermal variations of line widths in coronal holes and facular regions in a
number of spectral lines: H{\alpha}, He I 10830 {\AA}, Ca II 8542 {\AA}, Ba II
4554 {\AA}. In most cases, we detected associated intensity oscillations at
similar frequencies. Besides, we observed no centre-to-limb dependency. This
calls for a discussion on the practical validity of the method and on the
alternative explanations for the nature of non-thermal variations of spectral
line widths. Based on our observations, we consider registering line profile
broadening a necessary but not sufficient means for unambiguous identification
of torsional Alfv\'{e}n waves in the lower solar atmosphere
Multilevel Analysis of Oscillation Motions in Active Regions of the Sun
We present a new method that combines the results of an oscillation study
made in optical and radio observations. The optical spectral measurements in
photospheric and chromospheric lines of the line-of-sight velocity were carried
out at the Sayan Solar Observatory. The radio maps of the Sun were obtained
with the Nobeyama Radioheliograph at 1.76 cm. Radio sources associated with the
sunspots were analyzed to study the oscillation processes in the
chromosphere-corona transition region in the layer with magnetic field B=2000
G. A high level of instability of the oscillations in the optical and radio
data was found. We used a wavelet analysis for the spectra. The best
similarities of the spectra of oscillations obtained by the two methods were
detected in the three-minute oscillations inside the sunspot umbra for the
dates when the active regions were situated near the center of the solar disk.
A comparison of the wavelet spectra for optical and radio observations showed a
time delay of about 50 seconds of the radio results with respect to optical
ones. This implies a MHD wave traveling upward inside the umbral magnetic tube
of the sunspot. Besides three-minute and five-minute ones, oscillations with
longer periods (8 and 15 minutes) were detected in optical and radio records.Comment: 17 pages, 9 figures, accepted to Solar Physics (18 Jan 2011). The
final publication is available at http://www.springerlink.co
Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results
The chromosphere is a thin layer of the solar atmosphere that bridges the
relatively cool photosphere and the intensely heated transition region and
corona. Compressible and incompressible waves propagating through the
chromosphere can supply significant amounts of energy to the interface region
and corona. In recent years an abundance of high-resolution observations from
state-of-the-art facilities have provided new and exciting ways of
disentangling the characteristics of oscillatory phenomena propagating through
the dynamic chromosphere. Coupled with rapid advancements in
magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly
investigate the role waves play in supplying energy to sustain chromospheric
and coronal heating. Here, we review the recent progress made in
characterising, categorising and interpreting oscillations manifesting in the
solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review
Observations and mode identification of sausage waves in a magnetic pore
Aims. We aim to determine the phase speed of an oscillation in a magnetic pore using only intensity images at one height. The observations were obtained using the CRisp Imaging SpectroPolarimeter at the Swedisch 1-m Solar Telescope and show variations in both cross-sectional area and intensity in a magnetic pore.
Methods. We have designed and tested an observational method to extract the wave parameters that are important for seismology. We modelled the magnetic pore as a straight cylinder with a uniform plasma both inside and outside the flux tube and identify different wave modes. Using analytic expressions, we are able to distinguish between fast and slow modes and obtain the phase speed of the oscillations.
Results. We found that the observed oscillations are slow modes with a phase speed around 5 km s-1. We also have strong evidence that the oscillations are standing harmonics