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Hurbanovo, Slovakia

Freij N.,University of Sheffield | Dorotovic I.,Slovak Central Observatory | Morton R.J.,Northumbria University | Ruderman M.S.,University of Sheffield | And 4 more authors.
Astrophysical Journal

The presence of magnetoacoustic waves in magnetic structures in the solar atmosphere is well-documented. Applying the technique of solar magneto-seismology (SMS) allows us to infer the background properties of these structures. Here, we aim to identify properties of the observed magnetoacoustic waves and study the background properties of magnetic structures within the lower solar atmosphere. Using the Dutch Open Telescope and Rapid Oscillations in the Solar Atmosphere instruments, we captured two series of high-resolution intensity images with short cadences of two isolated magnetic pores. Combining wavelet analysis and empirical mode decomposition (EMD), we determined characteristic periods within the cross-sectional (i.e., area) and intensity time series. Then, by applying the theory of linear magnetohydrodynamics (MHD), we identified the mode of these oscillations within the MHD framework. Several oscillations have been detected within these two magnetic pores. Their periods range from 3 to 20 minutes. Combining wavelet analysis and EMD enables us to confidently find the phase difference between the area and intensity oscillations. From these observed features, we concluded that the detected oscillations can be classified as slow sausage MHD waves. Furthermore, we determined several key properties of these oscillations such as the radial velocity perturbation, the magnetic field perturbation, and the vertical wavenumber using SMS. The estimated range of the related wavenumbers reveals that these oscillations are trapped within these magnetic structures. Our results suggest that the detected oscillations are standing harmonics, and this allows us to estimate the expansion factor of the waveguides by employing SMS. The calculated expansion factor ranges from 4 to 12. © 2016. The American Astronomical Society. All rights reserved. Source

Prikryl P.,Natural Resources Canada | Prikryl P.,University of New Brunswick | Iwao K.,National Institute of Technology, Kumamoto College | Muldrew D.B.,Communications Research Center Canada | And 3 more authors.
Journal of Atmospheric and Solar-Terrestrial Physics

A link between solar wind magnetic sector boundary (heliospheric current sheet) crossings by the Earth and the upper-level tropospheric vorticity was discovered in the 1970s. These results have been later confirmed but the proposed mechanisms remain controversial. Extratropical-cyclone tracks obtained from two meteorological reanalysis datasets are used in superposed epoch analysis of time series of solar wind plasma parameters and green coronal emission line intensity. The time series are keyed to times of maximum growth of explosively developing extratropical cyclones in the winter season. The new statistical evidence corroborates the previously published results (Prikryl et al., 2009). This evidence shows that explosive extratropical cyclones tend to occur after arrivals of solar wind disturbances such as high-speed solar wind streams from coronal holes when large amplitude magneto-hydrodynamic waves couple to the magnetosphere-ionosphere system. These MHD waves modulate Joule heating and/or Lorentz forcing of the high-latitude thermosphere generating medium-scale atmospheric gravity waves that propagate energy upward and downward from auroral zone through the atmosphere. At the tropospheric level, in spite of significantly reduced amplitudes, these gravity waves can provide a lift of unstable air to release the moist symmetric instability thus initiating slantwise convection and forming cloud/precipitation bands. The release of latent heat is known to provide energy for rapid development and intensification of extratropical cyclones. © 2016 Elsevier Ltd. Source

Dorotovic I.,Slovak Central Observatory | Erdelyi R.,University of Sheffield | Freij N.,University of Sheffield | Karlovsky V.,Hlohovec Observatory and Planetarium | Marquez I.,Institute of Astrophysics of Canarias
Astronomy and Astrophysics

Aims. By focussing on the oscillations of the cross-sectional area and the total intensity of magnetic waveguides located in the lower solar atmosphere, we aim to detect and identify magnetohydrodynamic (MHD) sausage waves. Methods. Capturing several high-resolution time series of magnetic waveguides and employing a wavelet analysis, in conjunction with empirical mode decomposition (EMD), makes the MHD wave analysis possible. For this paper, two sunspots and one pore (with a light bridge) were chosen as examples of MHD waveguides in the lower solar atmosphere. Results. The waveguides display a range of periods from 4 to 65 min. These structures display in-phase behaviour between the area and intensity, presenting mounting evidence for sausage modes within these waveguides. The detected periods point towards standing oscillations. Conclusions. The presence of fast and slow MHD sausage waves has been detected in three different magnetic waveguides in the solar photosphere. Furthermore, these oscillations are potentially standing harmonics supported in the waveguides that are sandwiched vertically between the temperature minimum in the lower solar atmosphere and the transition region. The relevance of standing harmonic oscillations is that their exploitation by means of solar magneto-seismology may allow insight into the sub-pixel resolution structure of photospheric MHD waveguides. © ESO, 2014. Source

Lukac B.,Slovak Central Observatory | Rybansky M.,Slovak Academy of Sciences
Solar Physics

The original coronal index of the solar activity (CI) has been constructed on the basis of ground-based measurements of the intensities of the coronal line of 530. 3 nm (Rybanský in Bull. Astron. Inst. Czechoslov., 28, 367, 1975; Rybanský et al. in J. Geophys. Res., 110, A08106, 2005). In this paper, CI is compared with the EUV measurements on the CELIAS/SEM equipment based on the same idea as the original idea of the coronal index. The correlation is very good for the period 1996 - 2005 (r=0. 94 for daily values). The principal result of this paper is the introduction of the modified coronal index (MCI) which in all uses and contexts can replace the existing CI index. Daily MCI values extend over a time period of six solar activity cycles. Future MCI measurements will be derived from more reliable measurements made by space-based observatories that are not influenced by the weather. MCI measurements are and will continue to be archived at the web site of the Slovak Central Observatory in Hurbanovo (http://www.suh.sk/obs/vysl/MCI.htm). © Springer Science+Business Media B.V. 2010. Source

Lorenc M.,Slovak Central Observatory | Rybansky M.,Slovak Academy of Sciences | Dorotovic I.,Slovak Central Observatory
Solar Physics

We have studied the rotation of the solar corona using the images taken at a 9. 4 nm wavelength by the AIA 094 instrument on board the Solar Dynamics Observatory (SDO) satellite. Our analysis implies that the solar corona rotates differentially. It appears that ω, the angular rotation velocity of the solar corona, does not only depend on heliographic latitude but is also a function of time, while the nature of the latter dependence remains unclear. Besides measurement errors, deviations Δω from the mean rotational speed are also caused by proper motion of the observed point source (the tracer) with respect to its surroundings. The spread in ω values at a particular heliographic latitude is a real effect, not caused by measurement errors. Most of the observations carry relative error less than 1 % in ω. © 2012 Springer Science+Business Media B.V. Source

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