The effect of midnight temperature maximum winds on post-midnight
equatorial spread F
Abstract
The SAMI3/ESF (Sami3 is also a model of the ionosphere/equatorial spread
$F$) code is used to simulate the growth of equatorial plasma bubbles
in the presence of a background wind field based on measured winds. The
measured winds exhibit the well-known ‘midnight temperature maximum’
(MTM) pattern, in which an equatorward wind occurs simultaneously with a
cessation in the zonal wind. The MTM is often preceded by strong
equatorward winds (about 100 m/s). The circumstance where the MTM winds
are symmetric across the equator is considered; here the meridional wind
component in the southern hemisphere is the reverse of the northern
meridional wind. The timing of the wind pattern relative to the
imposition of a seed for the ESF instability is explored. We find that
the simultaneous occurrence of a seed wave and a strong converging
meridional wind pattern can produce post-midnight ESF. We further find
that the seed wave and the sudden cessation of the zonal winds can also
produce post-midnight ESF. The MENTAT (Magnetic mEridional NeuTrAl
Thermospheric) code verifies the occurrence of converging meridional
wind patterns such as those simulated here, based on ionosonde data.
Results suggest that regional-scale wind measurements would aid in the
prediction signal-disrupting ionospheric bubbles.