V. Kukhianidze

Doppler-shift oscillations in solar spicules

Aims. We analysed the consecutive height series of Hα 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. Our aim is to observe oscillatory phenomena in spicules and consequently to trace wave propagations through the chromosphere. Methods. We use the Discrete Fourier Transform analysis of Hα Doppler shift time series constructed from the observed spectra at each height. Results. Doppler velocities of solar limb spicules show oscillations with periods of 20−55 and 75−110 s. There is also clear evidence of 3-min oscillations at the observed heights. Conclusions. 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 of the wave excitation. Observed waves can be used as a tool for spicule seismology ,a nd the magnetic field strength in spicules at the height of ∼6000 km above the photosphere is estimated as 12−15 G.

Rieger-type periodicity during solar cycles 14-24: estimation of dynamo magnetic field strength in the solar interior

Solar activity undergoes a variation over time scales of several months known as Rieger-type periodicity, which usually occurs near maxima of sunspot cycles. An early analysis showed that the periodicity appears only in some cycles, and is absent in other cycles. But the appearance/absence during different cycles has not been explained. We performed a wavelet analysis of sunspot data from the Greenwich Royal Observatory and the Royal Observatory of Belgium during cycles 14-24. We found that the Rieger-type periods occur in all cycles, but they are cycle-dependent: shorter periods occur during stronger cycles. Our analysis revealed a periodicity of 185-195 days during the weak cycles 14-15 and 24, and a periodicity of 155-165 days during the stronger cycles 16-23. We derived the dispersion relation of the spherical harmonics of the magnetic Rossby waves in the presence of differential rotation and a toroidal magnetic field in the dynamo layer near the base of the convection zone. This showed that the harmonic of fast Rossby waves with m=1 and n=4, where m (n) indicate the toroidal (poloidal) wavenumbers, respectively, perfectly fit with the observed periodicity. The variation of the toroidal field strength from weaker to stronger cycles may lead to the different periods found in those cycles, which explains the observed enigmatic feature of the Rieger-type periodicity. Finally, we used the observed periodicity to estimate the dynamo field strength during cycles 14-24. Our estimations suggest a field strength of 40 kG for the stronger cycles, and 20 kG for the weaker cycles.

Formation and evolution of coronal rain observed by SDO/AIA on February 22, 2012

The formation and dynamics of coronal rain are currently not fully understood. Coronal rain is the fall of cool and dense blobs formed by thermal instability in the solar corona towards the solar surface with acceleration smaller than gravitational free fall. We aim to study the observational evidence of the formation of coronal rain and to trace the detailed dynamics of individual blobs. We used time series of the 171 \AA\, and 304 \AA\, spectral lines obtained by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) above active region AR 11420 on February 22, 2012. Observations show that a coronal loop disappeared in the 171 \AA\ channel and appeared in the 304 \AA\ line

North–South asymmetry in Rieger-type periodicity during Solar Cycles 19–23

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DYNAMICS OF A SOLAR PROMINENCE TORNADO OBSERVED BY SDO/AIA ON 2012 NOVEMBER 7–8

more than one hour later, which indicates a rapid cooling of the coronal loop from 1 MK to 0.05 MK. An energy estimation shows that the radiation is higher than the heat input, which indicates so-called catastrophic cooling. The cooling was accompanied by the formation of coronal rain in the form of falling cold plasma. We studied two different sequences of falling blobs. The first sequence includes three different blobs. The mean velocities of the blobs were estimated to be 50 km s

Statistical properties of coronal hole rotation rates: Are they linked to the solar interior?

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, 60 km s

Association between Tornadoes and Instability of Hosting Prominences

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Evidence for Precursors of the Coronal Hole Jets in Solar Bright Points

and 40 km s

Quasi-oscillatory dynamics observed in ascending phase of the flare on March 6, 2012

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