Iranian Journal of Astronomy and Astrophysic
Volume:10 Issue: 3, Autumn 2023

Sound waves have the potential to transfer the energy needed to heat the sun's atmosphere from the lower layers to higher areas. The source of these waves can be the surface oscillations of the sun, the most famous of which are the 5-minute oscillations. In this research, we investigate the propagation of sound waves in the first 2000 km of the sun's atmosphere, which is known as the chromosphere. In the chromosphere, variations in plasma density, hydrodynamic pressure, and temperature with height cause wave propagation to be complicated. Here, we build a chromospheric model using observational data and investigate sound propagation in both pulse and wave train modes. We solve the equation of motion numerically in the linear regime using the finite difference method. The results show that due to the reflection of the wave in different layers of the atmosphere, the sound pulse does not maintain its original shape, instead, its energy is spread in a wide space of the atmosphere. Also, for sinusoidal wave trains at different frequencies, we obtain the amount of the energy of the wave penetrating to the upper layers. Results show that as the frequency of the wave increases, the capability of the wave to transfer the acoustic energy from the photosphere to the upper chromosphere increases.

Arbitrary amplitude dust acoustic waves(DAWs) in a quantum dusty plasma including the effect of dust size distribution (DSD) is presented. By using the Sagdeev pseudopotential method for large amplitude waves, the energy integral is derived which includes Sagdeev potential. By applying the conditions in which a solitary solution can be existed, the upper and lower limits of Mach number is presented. Two cases are studied, a mono sized dust grains case and dust grains possessing power law size distribution case. The result shows that, the allowed Mach number’s range is increased for mono sized dust grains case. Sagdeev potential is also plotted and it is seen that in mono sized dust grains case, solitary waves are propagated. Whereas, for different sized dust grains having power law size distribution, the solitary waves transform into cnoidal ones.. The phase portrait is also plotted and comprised of Two different sets of orbits, a periodic orbit and a homoclinic one that correspond to periodic traveling wave solution and solitary wave solution, respectively

Various chromosphere and transition region jet-like structures abound playing an essential role in the dynamics and evolution therein. Tentatively identifying the wave characteristics and oscillatory behavior in the outer solar atmosphere helps to understand this layer better. In addition to the whip-like behavior, null-point motions in the reconnection site can excite transversal oscillation along the magnetical dense Jets, which is called the kink mode wave, and also this mode can evolve into Alfven wave after its propagation into the more homogeneous medium. The study of X-ray jets is an important topic in understanding the heating of the solar corona and the origin of the fast wind. The recently launched Hinode mission permitted us to observe the excellent proxies of these jets with an unprecedented high spatial resolution of 120 km on the Sun. We selected a high cadence sequence of SOT (Hinode) observations taken with both the HCaII and the Halpha filter to look at the details of the dynamics revealed by a significant jet event. Both wavelet and amplitude spectra analysis were used to analyze the observed kink wave and the time variations of intensities during the event. The results are discussed in the frame of different models implying reconnections with the inference of the dynamical phenomena occurring near several null points, including the oscillatory behavior.

Due to the massive increase in astronomical images (such as James Web, Solar Dynamic Observatory, and Solar Orbiter), automatic image description is essential for solar and astronomical. Zernike moments (ZMs) are unique due to the orthogonality and completeness of Zernike polynomials (ZPs); hence, ZMs are valuable for converting a two-dimensional image to a one-dimensional series of complex numbers. The magnitude of ZMs is rotation invariant, and by applying image normalization, scale and translation invariants can be made, which are helpful properties for describing solar and astronomical images. The lower-order ZMs express the overall shape of the objects of an image, and the higher-order ZMs provide more details of the objects and delicate structures within an image. In this Python package, available at GitHub and PyPI, we describe the characteristics of ZMs via several examples of solar (large and small scale) features, astronomical, and human face images. These independent and unique properties of ZMs can describe the structure and morphology of objects in an image. Hence, ZMs are helpful in machine learning to identify and track the features of several.

In order to study the nature of kink MHD waves, zero beta plasma in a thin twisted magnetic-flux tube is considered. We use two parameters, the ratio of restoring forces and the ratio of the parallel vorticity to the compressibility to study the effect of magnetic twist on the nature of kink waves. Our aim is to invstigate whether the nature of the wave obtained from studying these two parameters are the same or not. The two parameters give two different twist parameters in which the wave becomes purely Alfvénic. The first parameter indicates that both in the internal and external regionsof the tube, the wave can become purely magnetoacostic but the second parameter indicates that the wave can become magnetoacostic only in the external region of the tube. Our conclusion is that the two parameters are not equivalent for determining the nature of the wave.

Magnetic reconnection is a fundamental process in laboratory, astrophysical, and space plasmas, which is a mechanism for converting magnetic energy into the thermal and kinetic energy of plasma and the efficient acceleration of charged particles. Using two-dimensional magnetohydrodynamic simulations, we investigate the onset and the growth of instability associated with the forced magnetic reconnection phenomenon in the well-known equilibrium structure of the Harris current sheet in the presence of a resistive plasma. To derive externally the magnetic reconnection process, we perturb the velocity of plasma close to the up and down boundaries in the form of two localized pulses. The results show that these pulses propagate towards the current sheet, where the magnetic field changes direction, generates a perturbed magnetic field consequently, and triggers the magnetic reconnection phenomenon in an X-point in the center of the current sheet. We realized that increasing the amplitude of pulses results in a faster reconnection, and symmetric pulses are more efficient in conducting the reconnection. Furthermore, by imposing a transient (time-dependent) MHD wave normal to the current sheet, we found that an MHD wave with a more significant period (lower frequency) considerably affects the current sheet's topology and excites a faster reconnection. A similar conclusion was also obtained for an MHD wave with a larger wavelength (lower wavenumber). The obtained results are of interest for understanding the interaction of an MHD wave with an equilibrium current sheet in confined fusion plasmas and solar corona plasmas.