Abstract
This work presents equatorial ionospheric plasma bubble zonal drift
velocity observations and their comparison with model calculations. The
bubble zonal velocities were measured using airglow OI630 nm all-sky
digital images and the model calculations were performed taking into
account flux-tube integrated Pedersen conductivity and conductivity
weighted neutral zonal winds. The digital images were obtained from an
all-sky imaging system operated over the low-latitude station Cachoeira
Paulista (Geogr. 22.5S, 45W, dip angle 31.5S) during the period from
October 1998 to August 2000. Out of the 138 nights of imager
observation, 29 nights with the presence of plasma bubbles are used in
this study. These 29 nights correspond to geomagnetically rather quiet
days (Sigma K-p < 24+) and were grouped according to season. During the
early night hours, the calculated zonal drift velocities were found to
be larger than the experimental values. The best matching between the
calculated and observed zonal velocities were seen to be for a few hours
around midnight. The model calculation showed two humps around 20 LT and
24 LT that were not present in the data. Average decelerations obtained
from linear regression between 20 LT and 24 LT were found to be: (a)
Spring 1998, -8.61 ms(-1) h(-1); (b) Summer 1999, -0.59 ms(-1) h(-1);
(c) Spring 1999, -11.72 ms(-1) h(-1); and (d) Summer 2000, -8.59 ms(-1)
h(-1). Notice that Summer and Winter here correspond to southern
hemisphere Summer and Winter, not northern hemisphere. (c) 2006
Published by Elsevier Ltd on behalf of COSPAR.
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