The Role of Neutral Winds in Polar Cap Patch Instability Growth

Polar cap patches are regions of dense plasma in the polar cap that convect from noon to midnight, moving against the neutral gas background. The gradient drift instability (GDI) destabilizes the edge of these patches as they convect, yet the rate of this destabilization is not well known due to the scarcity of coincident neutral wind and plasma measurements. Polar cap patches detected by Swarm with conjunction measurements from GRACE‐FO are assessed for their GDI growth time with and without the neutral wind and for high and low collisionality regimes. This analysis shows significant differences in growth times with and without the neutral wind, and that the low collisionality growth times are different by a factor of 65%. These results demonstrate that coincident plasma and neutral wind measurements are essential for accurately determining how the GDI, and by extension polar cap patches, evolve.