Evidence for Deep Ingression of the Midlatitude MSTID Into As Low as similar to 3.5 degrees Magnetic Latitude

摘要

An observational evidence of medium-scale traveling ionospheric disturbances (MSTIDs) reaching to magnetic latitude as low as similar to 3.5 degrees 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 degrees N, 79.2 degrees E; 6.6 degrees 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 similar to 235 degrees +/- 1 degrees 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. Plain Language Summary Medium-scale traveling ionospheric disturbances (MSTIDs) generated in the midlatitude are found to propagate toward the equator. While crossing the equatorial ionization anomaly crest region most of these structures dissipate due to ion drag. A deep ingression of the MSTID to a very low geomagnetic latitude (near to the geomagnetic equator) over the Indian sector is noted during the descending phase of the 24th solar cycle. Weak and asymmetric equatorial ionization anomaly formation is believed to support the deep ingression processes. On the observational night quasiperiodic southward moving waves and a small-scale southward moving wave signature are also observed in addition with the MSTID. The dissipation of all these features is possibly due to existence of the midnight pressure bulge. Present study provides an observational evidence of the midlatitude MSTID propagation into the low latitudes and their interaction with the low-latitude ionospheric/thermospheric processes, for example, midnight pressure bulge.