A source or a sink? How the altitude of particle precipitation influence high-latitude electrodynamics

Abstract

From the sum total dissipation of unstable wave energy in geospace, a frequent and efficient channel of dissipation is opened up by particle precipitation. The phenomenon, which is part of a complicated cascade of unstable magnetohydrodynamic wave modes, consists of charged particles that intermittently rain down into Earth's dense atmosphere. The atmospheric penetration depth of the precipitating particles in aurorae dictates the altitude profile of plasma ionization. Absent of sunlight, this profile governs the crucial ratio of bottomside- to topside (E- to F-region) electrical conductance, which can act as a primary regulator of plasma turbulence growth rates by modulating the efficiency of electric field short-circuiting as well as ambipolar diffusion. Analyzing a large database of Defense Meteorological Satellite Program (DMSP) particle spectra from the dark, high-latitude ionosphere, we systematically map the response of this conductance ratio to varying geomagnetic activity. We reveal a characteristic spatial organization: during active conditions, the dayside cusp region is systematically drained of high-energy particles, creating a low-conductivity environment that favors the persistence of F-region turbulence, which starkly contrasts with the nightside auroral oval where elevated Pedersen conductivity in the E-region may actively dampen the growth of turbulence in the F-region. These findings indicate that the specific character of the magnetospheric energy input shapes the electrodynamics of specific regions, with implications for whether the ionosphere acts as a source or a sink for small-scale structuring.