Physics Dept Seminar

November 16th, Friday (*SPECIAL DAY*)

The Strange Case of Vigorous Thermospheric Vertical Winds in Aurora

Dr. John Meriwether 

Clemson University & NJIT

(Terrestrial Physics, Host: Gerrard)  

Room: ECE 202

*SPECIAL TIME: 2:45 pm - 3:45 pm with 2:30 pm tea time

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 Poker Flats (Alaska), Svalbard (northern Norway), and Andoya Space Center (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 quite a bit 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? In this talk I will present details describing an alternative explanation that is supported by recent theoretical modeling results presented by Lotko and Zhang. This proposed mechanism involving the absorption of Alfven waves produced within the magnetosphere-ionosphere interface is an excellent example of the importance of viewing the magnetosphere-ionosphere-thermosphere system as one coupled geospace system in which no one piece can be studied in isolation.