Generation of Alfvén waves by deceleration of magnetospheric convection and broadband PI pulsations

It is shown that Alfvén waves can be generated in the magnetosphere by the deceleration of magnetospheric convection due to the dynamo process in the magnetosphere‐ionosphere coupling. The growth rate of Alfvén wave packets bouncing between hemispheres is given by γ ≃ (2/µ0Σl) [αµ0²Σp²V0y² − 1] where α is a dimensionless constant (∼0.5), µ0 is the free space permeability, Σp is the height‐integrated Pedersen conductivity, l is the field line length between hemispheres, V0y is the convection speed in the magnetospheric dynamo region. Alfvén waves become unstable under disturbed conditions when both Σp and V0y are enhanced. The resulting unstable Alfvén waves can contribute to the Pi pulsations observed during substorms.