Trajectories of thermospheric air parcels flowing over Alaska, reconstructed from ground‐based wind measurements. Issue 6 (8th June 2017)

• Record Type: Journal Article
• Authors: Dhadly, Manbharat; Conde, Mark
• Is Part Of: Journal of geophysical research. Volume 122:Issue 6(2017)
• Page Start: 6635
• Page End: 6651
• Publication Date: 2017-06-08
• Subjects: thermospheric air parcel transport -- neutral wind‐driven transport -- air parcel tracing -- high‐latitude F region -- F region local‐scale structures; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1002/2017JA024095
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: It is widely presumed that the convective stability and enormous kinematic viscosity of Earth's upper thermosphere hinders development of both horizontal and vertical wind shears and other gradients. Any strong local structure (over scale sizes of several hundreds of kilometers) that might somehow form would be expected to dissipate rapidly. Air flow in such an atmosphere should be relatively simple, and transport effects only slowly disperse and mix air masses. However, our observations show that wind fields in Earth's thermosphere have much more local‐scale structure than usually predicated by current modeling techniques, at least at auroral latitudes; they complicate air parcel trajectories enormously, relative to typical expectations. For tracing air parcels, we used wind measurements of an all‐sky Scanning Doppler Fabry‐Perot interferometer and reconstructed time‐resolved two‐dimensional maps of the horizontal vector wind field to infer forward and backward air parcel trajectories over time. This is the first comprehensive study to visualize the complex motions of thermospheric air parcels carried through the actual observed local‐scale structures in the high‐latitude winds. Results show that thermospheric air parcel transport is a very difficult observational problem, because the trajectories followed are very sensitive to the detailed features of the driving wind field. To reconstruct the actual motion of a given air parcel requires wind measurements everywhere along the trajectory followed, with spatial resolutions of 100 km or less, and temporal resolutions of a few minutes or better. Understanding such transport is important, for example, in predicting the global‐scale impacts of aurorally generated composition perturbations. Key Points: First comprehensive study to visualize the complex motions of neutral air parcels carried through observed high‐latitude wind fields Local‐scale structures in high‐latitude winds complicate air parcel trajectories enormously, relative to typical expectations The trajectories followed are very sensitive to the detailed features of the driving wind field