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Ann. Geophys., 24, 1551-1565, 2006
www.ann-geophys.net/24/1551/2006/
© European Geosciences Union 2006
Sensitivity studies of the E region neutral response to the postmidnight diffuse aurora
H. F. Parish and L. R. Lyons
Department of Atmospheric and Oceanic Sciences, University of California Los Angeles, Los Angeles, CA 90095-1565, USA
Abstract. Measurements of the neutral thermosphere within the postmidnight substorm
recovery phase diffuse aurora show very large horizontal winds, and strong
vertical structure. Rocket, satellite, and ground based
observations during the ARIA (Atmospheric Response in Aurora) campaigns, and
earlier dawn side rocket observations, indicate neutral winds of up to 200 m/s,
and a characteristic jet-like wind maximum around 110 to 120-km altitude, with
strong shears above and below. The observed wind magnitudes are found to
have a dependence on geomagnetic activity level, but recent modeling
studies suggest that tides which propagate up from the troposphere and
stratosphere may play an important role in generating the strong vertical
variations in the neutral winds. The relative importance of auroral and
tidal forcing in producing the measured wind structure is not known, however.
Simulations have been performed using a three dimensional (3-D)
high resolution limited area thermosphere model to understand the processes
which generate the observed neutral structure within the postmidnight diffuse
aurora. Parameters measured during the ARIA I observational campaign have
been used to provide auroral forcing inputs for the model. Global background
winds and tides have been provided by the CTIP (Coupled Thermosphere
Ionosphere Plasmasphere) model. The sensitivity of the response of the
neutral atmosphere to changes in different parameters has been examined.
Variations in the amplitudes and phases of the propagating tides in the
background winds are found to have significant effects on the neutral
structure in the E region, and the wind structure below around
110km is found to be mainly produced by tidal forcing. Changes in the
electric field and ion density affect the winds above around 120 km, and
the importance of auroral forcing is found to depend on background
winds. Variations in the orientation of the aurora relative
to the background field, which may be caused by changes in the interplanetary
magnetic field, are also found to modify the wind structure. When both
auroral forcing and propagating tides are included, many of the basic
characteristics of the wind structure are displayed, although the great
strength of the wind shears is not well reproduced. The strength of the
shears may be related to a currently unmodeled process, or to different
types of waves.
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