This paper presents a three dimensional analysis of the properties of magneto hydrodynamic waves. A quantitative formulation of magneto hydrodynamic Alfvén waves is studied. On considering the motion in ordinary fluid, it is observed that the propagation of low frequency waves is only in the form of pressure waves. We have focused on such modes of propagation of incompressible fluid or plasma in magnetic field for which, the speed does not surpass the speed of sound. The value of conductivity is taken to be infinity and viscosity negligible. In such a case, the sum of the pressures of the field induced and the pressure of the plasma is independent of all the coordinates. The kinetic energy density of wave motion and the energy density of the field induced by the perturbation come out to be equal in both phase and amplitude. The study of the effect of large but finite conductivity for small Joule losses reveal that the waves remain periodic, but it is observed that the amplitude of the waves decreases continuously and exponentially at a slow pace.
In this paper, a broad examination of the N-S asymmetry of daily sunspot numbers during the period January 1992 to March 2020 has been performed, examining its statistical significance and looking for the short term periodicity of daily sunspot numbers using the Fast Fourier Transform (FFT) during solar cycle 22 (1 January 1986 to 27 August 1996), cycle 23 (28 August 1996 to 10 December 2008) and cycle 24 (11 December 2008 to 31 March 2020). The present study indicates that sunspot number activity dominates in the southern hemisphere during the solar cycles 22 and 23, while during the solar cycle 24, the sunspot number becomes dominant in the northern hemisphere. It is also revealed that the magnitude of sunspot number activity for solar cycle 23 is more prominent in both the northern and southern hemispheres than in solar cycles 22 and 24. The power spectrum of daily sunspot numbers shows several significant periodicities in a wide range between 26 days and 83 days. We discuss the possible explanations of the observed periodicities and north-south asymmetry of the daily sunspot number in light of previous results and existing techniques.
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