Wind-driven transport of thermospheric air parcels in the auroral zone

Data from ground-based optical instruments at Poker Flat and Fort Yukon in Alaska recorded during 2010 were used to examine the relationship between composition changes in the auroral thermosphere and transport effects by neutral winds. Thermospheric column [O]/[N2] estimates were obtained from a pair of four-channel zenith-pointed narrow field photometers located at Poker Flat and Fort Yukon, whereas neutral winds at E and F-region heights were measured using an all-sky imaging Fabry-Perot spectrometer at Poker Flat. Wind fields were obtained over a spatial region around 1400 km in diameter in the F-region, or 700 km in the E-region, with a cadence of one observation every few minutes. We focus in particular on a sustained depletion of column [O]/[N2] observed during the minor storm period of April 4-8, 2010. While various correlated events were noted, no systematic relation was found between between horizontal winds and the column [O]/[N2] during this period (or indeed on any of the several tens of other days that we examined.) However during the storm there was a very obvious increase in activity of vertical winds, horizontal divergence, and associated wave activity. We suggest that the long-lived decrease in column [O]/[N2] during the storm was due to vertical mixing being enhanced by a process akin to eddy diffusion. This is in contrast to the more typical picture of localized “upwellings” being driven by Joule heating, and then carrying molecular species aloft