Physics Department Seminar University of Alaska Fairbanks

J O U R N A L    C L U B


The strange case of vigorous thermospheric vertical winds in aurora

John Meriwether
Department of Physics and Astronomy Clemson University - NJIT



It has been the conventional wisdom since the beginning of the application of the Fabry-Perot interferometer to the measurements of the thermospheric wind vector components (vertical and horizontal) that the vertical velocity of the thermospheric wind of the upper atmosphere is expected to be small, no more than several ms-1. Yet, from the beginning of the collection of auroral FPI measurements, anomalous vertical wind results have been reported, most notably those of Aruliah and Rees (1991). In this talk FPI results obtained in Alaska and Norway will be presented showing that quite typically upward vertical winds with speeds as much as 25 to 100 ms-1 have been seen. What is even more of a puzzle is the finding that such vertical wind activity and related thermospheric heating can be sustained over periods of hours. Such results indicate that the dynamics of the thermosphere during active aurora is far more vigorous than we might otherwise have imagined. The simplest explanation is likely a heating mechanism as any other mechanism would seem less credible. However, high altitude Joule heating ( h > 200 km) is believed to be inadequate to the production of such vigorous activity for altitudes above 225 km. What then would be an appropriate heating mechanism? Moreover, is it conceivable that waves from below might be the source? A possible explanation suggesting a new thermosphere heating mechanism is supported by recent theoretical modeling results presented by Lotko and Zhang that suggests the absorption of Alfven waves produced within the magnetosphere-ionosphere interface might be credible. In any case, the importance of viewing the magnetosphere-ionosphere-thermosphere system as one coupled geospace system in which no one piece can be studied in isolation cannot be over-emphasized.


Friday, 25 January 2019

Globe Room, Elvey Building