The Case for a New Process, not Mechanism, for Cusp Irregularity Production

Carlson, H.1, Pedersen, T.2, Basu, Santi2 and Moen, J.3

1 Utah State University, University of Oslo, USA and Norway
3 University of Oslo/UNIS, Norway

Two plasma instability mechanisms are currently thought to dominate formation of plasma irregularities in the F region high latitude and polar ionosphere: the gradient-drift driven instability, and velocity-shear driven instability. The former mechanism is accepted as accounting for structuring plasma in polar cap patches, the latter for structuring plasma in polar cap sun aligned arcs. This structuring, studied intensively for both scientific and practical reasons, leads to phase and amplitude scintillation capable of disrupting satellite communications and navigation signals. Here we introduce not a new mechanism, but a needed new process of orthogonal mixing of these two instability mechanisms, which drives severe structuring and scintillation in plasma entering the polar cap through the cusp. Correct modeling of cusp and early polar cap patch structuring will not be accomplished without allowing for this compound process. This compound process also explains previously unexplained characteristics of cusp and early polar cap patch irregularities.