Ionospheric Irregularity Zonal VelocitiesOver Cachoeira-Paulista
Journal of Atmospheric and Solar-Terrestrial Physics
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 630 nm all-sky images. The average decimetric solar =ux index for this period of increasing solar activity was about 145 and magnetically quiet days with Kp¡24 were selected. The GPS technique used receivers spaced 55 m in the magnetic east–west direction and probed small scale plasma structures (scale size about 400 m) at altitudes near 350 km. The zonal irregularity drift velocities measured by this technique were eastward with values of about 160 m=s at 20 LT, about 140 m=s around midnight, and decreased further in the post-midnight sector. The variability of these drifts decreased signi?cantly after midnight. The zonal velocities of large scale plasma structure were obtained using OI 630 nm all-sky images from a region located about 24:1◦S and 45◦W at a nominal height of 250 km which corresponds to the bubble projection along the magnetic ?eld lines to 350 km 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.
dePaula, E.R., I.J. Kantor, J.H.A. Sobral, H. Takahashi, D.C. Santana, D. Gobbi, A.F. Medeiros, L.A.T. Limiro, H. Kil, P.M. Kintner, and M.J. Taylor, Ionospheric irregularity zonal velocities over Cachoeira-Paulista, , J. Atmos. Solar-Terr. Phys., 64, 1511-1516, 2002.