Abstract:
An observational evidence of medium‐scale traveling ionospheric disturbances (MSTIDs) reaching to
magnetic latitude as low as ~3.5° over the Indian sector is provided for the first time based on OI 630‐nm
airglow imaging observation from a low‐latitude station, Gadanki (13.5°N, 79.2°E; 6.6° magnetic latitude),
on 12 January 2016. The horizontal wavelength, horizontal phase velocity, and period of the MSTID are
found to be 160 ± 6 km, 138 ± 14 m/s, and 19.5 ± 3 min, respectively. These phase fronts are observed to
move toward southwest with a propagation angle of ~235° ± 1° with respect to north. In addition to the
MSTID, a strong quasiperiodic southward moving wave (QPSMW) from the evening to midnight interval
and a small‐scale southward moving wave structure with wavelength and periodicity different from the
QPSMW are also detected on the same night. Horizontal wavelength, horizontal phase velocity, and period
of the QPSMW are estimated to be 367 ± 14 km, 131 ± 18 m/s, and 46.7 ± 13 min, respectively, and those of
the small‐scale southward moving wave are found to be 157 ± 4 km, 121 ± 17.8 m/s, and 21.7 ± 3.4 min,
respectively. Global Positioning System‐total electron content maps suggest that the weak and asymmetric
equatorial ionization anomaly helped deep ingression of the MSTID on this night. The descent of the F layer
seems to have caused the dissipation of the MSTID and QPSMW closer to the dip equator on this night.
Therefore, the present investigation shows that the midlatitude MSTIDs can influence the F region plasma
processes even over very low latitudes under favorable background conditions.
