Overreflection of Alfvenic wave modes (modified by Keplerian rotation) in astrophysical disks at weak azimuthal magnetic field

**Authors:** Mariami Kavtaradze, Revaz Chanishvili **Affiliations:** Georgian National Astrophysical Observatory, Abastumani 0301, Georgia; Department of Physics, Faculty of Exact and Natural Sciences, Javakhishvili Tbilisi State University, Tbilisi 0179, Georgia The main aim of the present research is the investigation of the linear dynamics of wave modes in strongly sheared, incompressible Keplerian disks with a background azimuthal magnetic field. In the asymptotic (WKB) approximation, we derive the dispersion relation and classify two modes of the flow - inertial and magnetic modes – that reduce to Alfvén waves for sufficiently large shearwise wavenumber. We study the dynamics of each mode of the flow in the framework of the nonmodal approach. We analyzed cases of dynamics with different mode harmonics imposed initially, with wavenumbers satisfing the condition -k_x (0)/k_y≫1,k_z=k_y. In all cases, all mode harmonics undergo transient (nonmodal) growth followed by mode coupling near zero shearwise wavenumber. The energy of the system increases by a factor of 100 when the magnetic mode is imposed initially, compared to the case when the inertial mode is imposed initially. Consequently, magnetic modes modified by Keplerian rotation play a crucial role in the onset of turbulence in this spectrally stable shear flow. Additionally, we found that when the magnetic mode is imposed initially, after transient growth and overreflection phenomena, perturbation modes of the flow become balanced. This contrasts with scenario where the initially imposed mode is inertial. These findings form the basis for future nonlinear studies.