All-sky imaging observations of conjugate medium-scale traveling ionospheric disturbances in the American sector

All-sky imaging systems at Arecibo, Puerto Rico (18.3 degrees N, 66.7 degrees W, +28 degrees mag. lat.), and Mercedes, Argentina (34.6 degrees S, 59.4 degrees W, -24.6 degrees mag. lat.), are used to study ionospheric conjugate processes at lower midlatitudes. For the first time in the American sector the simultaneous occurrence in both hemispheres of medium-scale traveling ionospheric disturbances has been observed. The first year of observations yielded 43 nights (similar to 40%) with simultaneous occurrence of airglow bands. Supporting information from GPS receivers indicate the presence of vertical total electron content variations that correlate with the airglow structures observed with the imagers. Weak phase fluctuations have been measured, indicating that these structures do not produce severe large-scale ionospheric irregularities.