Article

Ionospheric irregularity zonal velocities over Cachoeira Paulista

Cornell University, 304 Rhodes Hall, Ithaca, NY 14852-3801, USA
Journal of Atmospheric and Solar-Terrestrial Physics (Impact Factor: 1.75). 08/2002; 64(12):1511-1516. DOI: 10.1016/S1364-6826(02)00088-3

ABSTRACT We have studied the zonal drift velocity of nighttime ionospheric irregularities from Cachoeira Paulista (22.41°S,45°W, dip latitude −17.43°), a station under the Equatorial Anomaly, from December 1998 to February 1999 using L1 band GPS receivers and OI all-sky images. The average decimetric solar flux index for this period of increasing solar activity was about 145 and magnetically quiet days with ΣKp<24 were selected. The GPS technique used receivers spaced in the magnetic east–west direction and probed small scale plasma structures (scale size about ) at altitudes near . The zonal irregularity drift velocities measured by this technique were eastward with values of about at 20 LT, about around midnight, and decreased further in the post-midnight sector. The variability of these drifts decreased significantly after midnight. The zonal velocities of large scale plasma structure were obtained using OI all-sky images from a region located about 24.1°S and 45°W at a nominal height of which corresponds to the bubble projection along the magnetic field lines to over Cachoeira Paulista. These all-sky imager derived zonal drifts are also eastward, but have magnitudes smaller than the spaced GPS eastward drifts, particularly in the pre-midnight sector. We will discuss these two drift measurement techniques and the interpretation of our results.

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    • "The climatological model of Fejer et al. [2005] reveals the zonal drifts to vary from 100 m/s to 170 m/s. The peak drift velocities calculated from optical measurements over American sector are found to be ~120 m/s to ~150 m/s [e.g., de Paula et al., 2002; Martinis et al., 2003; Pimenta et al., 2003]. Over Indian sector, using VHF scintillation data, Kumar et al. [1995] reported the drift velocities to decrease from ~200 m/s at 2000 h IST to ~60 m/s at 0400 h IST. "
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    • "Although there are a number of papers on the zonal plasma drift, a large number of those studies are restricted to local nighttime because they used equatorial plasma bubbles (EPBs) as a tracer for estimating the zonal plasma drift (e.g. Kil et al., 2002; de Paula et al., 2002; Martinis et al., 2003; England and Immel, 2012). Some of the other extensive studies , which covered the dayside climatology, used groundbased instrumentation at a fixed geographic location (e.g. "
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    • "dip angle at 300 km$ 201S). The large-scale plasma depletions/ irregularities have been widely reported to move eastward as measured by different techniques (Sobral et al., 1980a,1980b, 1985, 2009; Mendillo and Baumgardner, 1982; Abdu et al., 1985, 1987; Taylor et al., 1997; Rohrbaugh et al., 1989; Fejer et al., 1981, 1985, 1991, 2005; Sobral and Abdu, 1990; Basu et al., 1996, 2004; Valladares et al., 1996; Fagundes et al., 1996, 1997, 1998; Kudeki and Bhattacharyya, 1999; Kil et al., 2000; Bhattacharyya et al., 2001; Pimenta et al., 2001, 2003a, 2003b; de Paula et al., 2002; Otsuka et al., 2002, 2004; Immel et al., 2003, 2004; Kelley et al., 2003; Martinis et al., 2003; Makela, 2003, 2006 Abalde et al., 2004; Sheehan and Valladares, 2004; Lin et al., 2005; Ogawa et al., 2005; Park et al., 2007). However in considerably less frequent cases westward zonal motions have been observed, almost all of which being related to disturbance dynamo electric fields that are formed during geomagnetically disturbed time. "
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