Ionospheric irregularity zonal velocities over Cachoeira Paulista

INPE-DAE, CP 515, 12.201-970, São José dos Campos, SP, Brazil; Johns Hopkins APL, 11100 Johns Hopkins Road, #7-324, Laurel, MD, USA; Cornell University, 304 Rhodes Hall, Ithaca, NY 14852-3801, USA; Utah State University, Logan, UT 84322-4145, USA
Journal of Atmospheric and Solar-Terrestrial Physics (Impact Factor: 1.42). 01/2002; 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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