Interaction of oppositely traveling medium�scale traveling ionospheric disturbances observed in low latitudes during geomagnetically quiet nighttime

In this study, an unusual event of medium-scale traveling ionospheric disturbances (MSTIDs) that propagated in opposite directions was observed by multi-instruments (all-sky imager, global positioning system (GPS), and digisonde) in low latitudes during geomagnetically quiet nighttime. These MSTIDs had wavefronts aligned from northwest to southeast. One MSTID propagated southwestward and another propagated northeastward. They encountered and interacted with each other. Some MSTIDs structures merged into one and disappeared after the interaction. Furthermore, an eastward moving plasma bubble also encountered the MSTIDs and then gradually dissipated during the propagation process. The MSTIDs traveling in opposite directions should be related to ionospheric plasma motion and their trigger mechanisms. The interactive process of MSTIDS involved in plasma drifts and polarization electric fields. Meanwhile, the interaction with an ionospheric irregularity structure can change some of the MSTID characteristics.