Effects of Asymmetry between the Northern and Southern Latitudes on ULF Waves near the Equatorial Region

Abstract:

Magnetic equator may have asymmetric wave properties between the northern and southern magnetospheres owing to magnetic geometry, field-aligned inhomogeneity as well as ionospheric conductivities. By using a three-dimensional dipole wave model, We study how ULF waves are affected by such north-south asymmetry. Firstly, we present how odd and even harmonics of both toroidal and poloidal modes are excited respectively when N-S asymmetry gradually increases. Our initial results are compared to the previous studies of magnetoseismology. Secondly, we show how ULF waves are excited by assuming various asymmetric field-aligned models. While magnetic geometry remains symmetric, asymmetry is introduced owing to field-aligned inhomogeneity and/or differential ionospheric conductivities. It is shown that field-aligned asymmetry highly enhances the damping process of poloidal modes and reduces their lifetime by the mismatch between symmetric bounce-drift motion and asymmetric field-aligned mode structure. The time-dependent feature is examined at different locations including the equatorial region. In addition, we discuss about the minimal conditions that support the excitation of the poloidal modes associated with wave-particle interaction.