Neutral wind structures in the upper thermosphere observed with the two FPIs in association with auroral heating

*Shin-ichiro Oyama[1] ,Hiroyuki Shinagawa [2]
Mamoru Ishii [1],Mark Conde [3]
Communications Research Laboratory[1]
Solar-Terrestrial Environment Laboratory, Nagoya University[2]
Geophysical Institute, University of Alaska Fairbanks[3]

In this paper, we will show two types of thermospheric responses to auroral heating using data from two FPIs (630.0 nm); the all-sky FPI and the FPI with narrow view angle at Poker Flat, Alaska (65.11 N, 147.42 W). One is that auroral heating regions have relatively stable temporal and spatial variations, and vertical winds have long time- scale variations with amplitude of more than 20 m/s. Other is that vertical winds fluctuate changing their sign with a magnitude of more than 40 m/s in association with poleward expansion of auroral arc.

The auroral thermosphere is a region where a number of phys ical and chemical processes occurs due to perturbations in t he auroral electrojet current, auroral heating caused by highly energetic particles from the magnetosphere, and rapid motions of the auroral arc. Those processes modify the wind and temperature structures generated by solar heating alone.
Recent observations at high latitudes with a ground-based Fabry-Perot interferometer (FPI, 630.0 nm) show latitudinal shear of the geomagnetic zonal wind in the premidnight time sector in association with both the equatorward and poleward boundaries of the discrete aurora [Conde et al., 2001]. Model calculations showed that the ion-drag acceleration of neutral wind could lead to the development of significant horizontal wind shears [Lyons and Walterscheid, 1985; Keskinen and Satyanarayana, 1993].
In the auroral thermosphere, vertical components of neutral winds have been observed with FPIs and satellites, which have significantly large amplitude than we predicted with theoretical calculations. Vertical mixture in the thermospheric species varies ionospheric and thermospheric conditions through chemical and physical processes. Temperature drops of about 100 K together with upward winds in the upper thermosphere were observed with Dynamics Explorer 2 satellite [Eastes et al., 1992], which may relate to adiabatic and/or radiation cooling due to the upward transport of molecular species in the lower thermosphere [Maeda et al., 1989].
In this paper, we will show two types of thermospheric responses to auroral heating using data from two FPIs (630.0 nm); the all-sky FPI and the FPI with narrow view angle at Poker Flat, Alaska (65.11 N, 147.42 W). One is that auroral heating regions have relatively stable temporal and spatial variations, and vertical winds have long time- scale variations with amplitude of more than 20 m/s. Other is that vertical winds fluctuate changing their sign with a magnitude of more than 40 m/s in association with poleward expansion of auroral arc. These observed results will be compared with a high-resolution two-dimensional nonhydrostatic compressible thermospheric model results by Shinagawa in this session. To provide realistic parameters for model calculations, we estimated auroral heating region using data from the meridian scanning-photometer at Poker Flat and the VHF radar at Anchorage, Alaska (61.15 N, 149.48 W).
References
Conde et al., J. Geophys. Res., 106, 10,493, 2001.
Eastes et al., J. Geophys. Res., 97, 10,539, 1992.
Keskinen and Satyanarayana, Geophys. Res. Lett., 20, 2687, 1993.
Lyons and Walterscheid, J. Geophys. Res., 90, 12,321, 1985.
Maeda et al., J. Geophys. Res., 94, 16,869, 1989.