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Ann. Geophys., 26, 2649-2655, 2008
www.ann-geophys.net/26/2649/2008/
© European Geosciences Union 2008
Upper thermospheric neutral wind and temperature measurements from an extended spatial field
E. M. Griffin1, A. L. Aruliah1, I. McWhirter1, H.-C. I. Yiu1, A. Charalambous1, and I. McCrea2
1Atmospheric Physics Laboratory, University College London, Gower Street, London WC1E 6BT, UK
2EISCAT Support Group, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, UK
Abstract. First results are presented from a Scanning Doppler Imager (SCANDI)
installed at the Nordlysstasjonen optical observatory near Longyearbyen,
Svalbard (78.2° N, 15.8° E). Observations of the atomic oxygen 630 nm
red line emission, originating in the upper thermosphere at around 250 km,
have been used to determine neutral winds and temperatures from multiple
zones within an extended spatial field. The instrument utilises all-sky
optics to achieve multiple simultaneous measurements, compared to the
standard Fabry-Perot Interferometer (FPI) procedure of separate
line-of-sight samples within a sequence of narrow angle look directions.
SCANDI is colocated with such a standard FPI and comparison of neutral wind
velocities between the instruments on the night of 15 March 2007 has
revealed detailed and consistent structure in the wind field. Southward
meridional wind enhancements of several hundred m/s are observed
simultaneously with both instruments, revealing structure on scales not
currently considered in thermospheric general circulation models (GCMs). The
data from this night also demonstrate the influence of discrete auroral
events on thermospheric behaviour. High intensities observed by SCANDI in
the presence of auroral arcs coincide with a drop in measured neutral
temperatures. This is interpreted as a result of the effective altitude of
the 630 nm emission being lowered under conditions of soft auroral
precipitation. The optical instruments as a consequence sample a region of
lower temperature. This effect has been observed previously with lower
thermospheric atomic oxygen emissions at 557.7 nm. The EISCAT Svalbard Radar
(ESR) provides ion temperatures and electron densities for the night which
confirm the influence of precipitation and heating during the auroral
events. The minima of ion temperatures through the pre-midnight period
provide a good match to the neutral temperatures measured with SCANDI, and
to the colocated FPI temperatures.
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