Abstract
The magnetosheath is a region located between the bow shock and the Earth's magnetopause. The importance of the Earth's magnetosheath in space physics is related to its role as a mediator between the solar wind and terrestrial magnetosphere. The magnetosheath should play an important role in the transmission of matter and energy observed in the solar wind through to the magnetopause. Several theoretical models have been developed to understand the plasma and magnetic field properties in the magnetosheath. These models differ in the role that the magnetic forces play in them. The interaction of the magnetosheath with the magnetopause can be described in terms of waves. These waves in general can take various forms, such as oscillation, discontinuities or standing waves and infinitesimal increments. The function of these waves is to reconfigure the solar wind flow and its frozen-in magnetic field from the solar wind state to the state specified by the magnetopause boundary condition. The main characteristics and positions of the wave modes in the Earth's magnetosheath are briefly summarized. In this paper we estimated the periodicity of the wave modes across the Earth's magnetosheath using Eigen modes of the global magnetosphere and ideal gas model. In the ideal gas model, we found two values of the periodicity of the Alfven waves corresponding to two different positions in the magnetosheath. The first is, (similar to 20.4 min) at the magnetopause, while the second is (similar to 42.36 min) at the bow shock. For the Eigen modes of the global magnetosphere, the periodicity is about (similar to 16.59 min). From our calculations, we concluded that the Alfven waves could propagate near the inner magnetosheath (at the magnetopause) with shorter periodicity than at the bow shock. These waves should play the required role to explain the observed transfer of matter and energy from the solar wind into the magnetopause.