All‐sky imagers located at Tucumán, Argentina (26.9°S, 65°W, 14.2°S dip latitude), and Arequipa, Perú (16.5°S, 71.5°W, 2.7°S dip latitude), are used to track 630 nm airglow depletion motions in the first use of multisite airglow imagers for studies of low‐latitude plasma dynamics. A new image analysis technique yields a consistent determination of nighttime zonal plasma drifts from all‐sky images of the depletion motions. The observed eastward plasma drifts are smaller at Arequipa than at Tucumán in the postsunset period. During the postmidnight hours, the opposite pattern occurs. These observations are interpreted using the simple plasma drift model and coupled ionosphere‐electric field model of Eccles [1998a, 1998b]. The observed zonal plasma drifts result from low‐latitude electrodynamics with a mix of influences from E and F region conductivities and neutral wind shears in altitude and latitude. Analysis of the observations suggests that postsunset zonal drifts near the magnetic equator (Arequipa) are strongly influenced by the E region dynamo, while the F region dynamo is the main cause of zonal drifts observed closer to the Equatorial Ionization Anomaly (Tucumán). The observed altitude‐latitude behavior of the plasma drifts gives the first two‐dimensional evidence for the so‐called F region plasma vortex's influence at equatorial and low latitudes obtained using optical imaging techniques. With this framework a synthesis is offered for seemingly inconsistent zonal drift observations in the published literature.

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A method to obtain the total electron content (TEC) of the ionosphere over Tucumán (26.9° S; 65.4° W), from ionogram data alone, is reported. To accomplish this, two Chapman profile expressions for the electron density (n) distribution in the F region are assumed, and a characteristic point of the n profile, called F region base point, is required. This method allows the TEC for a given particular time (not average) to be obtained. The results suggest that it could be a new method to calibrate polarimeter records used to measure TEC, and it could also allow the determination of TEC at predawn hours where only ionosounder data are available.

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