Upper atmosphere wind driven transport

What is it about?

It is widely presumed that 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. 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.

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Why is it important?

Understanding thermospheric wind-driven transport, especially at high latitudes, is one of the long-standing challenges of the global space weather research. Over the past two decades, even though a considerable amount of research effort has been focused on understanding thermospheric wind behavior, a little attention was focused on wind-driven local-scale transport in the thermosphere. This is primarily because of (1) the scarcity of high spatiotemporal resolution observational wind data with continuous and wide geographic coverage and (2) inability to accurately model thermospheric winds from first principles over local scales. Thus, this topic has remained one of the least studied components of high-latitude aeronomy. The results presented here are the first comprehensive study to visualize the complex motions of thermospheric air parcels through the actual observed local-scale structures in the high-latitude wind fields.

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