9 research outputs found
Contribution to the modeling of solar spicules
Solar limb and disc spicule quasi- periodic motions have been reported for a
long time, strongly suggesting that they are oscillating. In order to clear up
the origin and possibly explain some solar limb and disc spicule quasi-periodic
recurrences produced by overlapping effects, we present a simulation model
assuming quasi- random positions of spicules. We also allow a set number of
spicules with different physical properties (such as: height, lifetime and tilt
angle as shown by an individual spicule) occurring randomly.
Results of simulations made with three different spatial resolutions of the
corresponding frames and also for different number density of spicules, are
analyzed. The wavelet time/frequency method is used to obtain the exact period
of spicule visibility. Results are compared with observations of the
chromosphere from i/ the Transition Region and Coronal Explorer (TRACE)
filtergrams taken at 1600 angstrom, ii/ the Solar Optical Telescope (SOT) of
Hinode taken in the Ca II H-line and iii/ the Sac-Peak Dunn's VTT taken in
H{\alpha} line. Our results suggest the need to be cautious when interpreting
apparent oscillations seen in spicule image sequences when overlapping is
present, i.e.; when the spatial resolution is not enough to resolve individual
components of spicules.Comment: 20 pages, 7 figures, 1 tabl
Doppler shift oscillations in solar spicules
Consecutive height series of Ha spectra in solar limb spicules taken on the
53 cm coronagraph of Abastumani Astrophysical Observatory at the heights of
3800-8700 km above the photosphere have been analyzed. The aim is to observe
oscillatory phenomena in spicules and consequently to trace wave propagations
through the chromosphere. The Discrete Fourier Transform analysis of Ha Doppler
shift time series constructed from the observed spectra at each height is used.
Doppler velocities of solar limb spicules show oscillations with periods of
20-55 and 75-110 s. There is also the clear evidence of 3-min oscillations at
the observed heights. The oscillations can be caused by wave propagations in
thin magnetic flux tubes anchored in the photosphere. We suggest the
granulation as a possible source for the wave excitation. Observed waves can be
used as a tool for spicule seismology; the magnetic field strength in spicules
at the height of about 6000 km above the photosphere is estimated as 12-15 G.Comment: 7 pages, 8 figures, accepted in A&
Magneto-Acoustic Wave Oscillations in Solar Spicules
Some observations suggest that solar spicules show small amplitude and high
frequency oscillations of magneto-acoustic waves, which arise from photospheric
granular forcing. We apply the method of MHD seismology to determine the period
of kink waves. For this purposes, the oscillations of a magnetic cylinder
embedded in a field-free environment is investigated. Finally, diagnostic
diagrams displaying the oscillatory period in terms of some equilibrium
parameters are provided to allow a comparison between theoretical results and
those coming from observations.Comment: 10 pages, 4 fig
Observation of kink waves in solar spicules
Height series of H spectra in solar limb spicules obtained with the
53 cm coronagraph of the Abastumani Astrophysical Observatory are analyzed.
Each height series covered 8 different heights beginning at 3800 km above the
photosphere. The spatial difference between neighboring heights was 1, consequently 3800 - 8700 km distance above the photosphere has
been covered. The total time duration of each height series was 7 s. We found
that nearly 20% of measured height series show a periodic spatial distribution
of Doppler velocities. We suggest that this spatial periodicity in Doppler
velocity is caused by propagating kink waves in spicules. The wave length is
found to be 3500 km. However the wave length tends to be 1000 km
at the photosphere due to the height variation of the kink speed. This probably
indicates to a granular origin for the waves. The period of waves is estimated
to be in the range of 35-70 s. These waves may carry photospheric energy into
the corona, therefore can be of importance in coronal heating.Comment: 4 pages, 4 figures, Accepted in A&
Oscillations and waves in solar spicules
Since their discovery, spicules have attracted increased attention as energy/mass bridges between the dense and dynamic photosphere and the tenuous hot solar corona. Mechanical energy of photospheric random and coherent motions can be guided by magnetic field lines, spanning from the interior to the upper parts of the solar atmosphere, in the form of waves and oscillations. Since spicules are one of the most pronounced features of the chromosphere, the energy transport they participate in can be traced by the observations of their oscillatory motions. Oscillations in spicules have been observed for a long time. However the recent high-resolutions and high-cadence space and ground based facilities with superb spatial, temporal and spectral capacities brought new aspects in the research of spicule dynamics. Here we review the progress made in imaging and spectroscopic observations of waves and oscillations in spicules. The observations are accompanied by a discussion on theoretical modelling and interpretations of these oscillations. Finally, we embark on the recent developments made on the presence and role of Alfven and kink waves in spicules. We also address the extensive debate made on the Alfven versus kink waves in the context of the explanation of the observed transverse oscillations of spicule axes