Simultaneous Observations of Quasi‐Orthogonal Nighttime MSTIDs at Conjugate African‐European Midlatitude Stations on 4 October 2018

Abstract Two quasi‐orthogonal nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) were observed by conjugate midlatitude all‐sky imagers in Sutherland (32.4S, 20.8E; magnetic latitude: −40.9) and Asiago (45.87N, 11.53E; magnetic latitude: ) on 4 October 2018. These MSTIDs had fronts elongated quasi‐orthogonally to one another as observed from each location. The first MSTID was aligned northeast‐southwest (NE‐SW) in the Southern Hemisphere (SH) and northwest‐southeast (NW‐SE) in the Northern Hemisphere (NH) and propagated equator‐westwards. These properties are typically attributed to MSTIDs generated through the coupled Perkins and sporadic E instabilities. This is supported by observed conditions in both hemispheres indicating the presence of sporadic E layers and reasonable Perkins instability growth rates. The second MSTID was aligned NW‐SE (SH) and NE‐SW (NH) and propagated equator‐eastwards and represents the first optical observations of conjugate equator‐eastward propagating MSTIDs. A possible linkage to gravity wave‐induced polarization electric fields in the NH (and mapped to the SH) is presented, as significant gravity wave activity was observed in OH and OI greenline observations by the Asiago imager. Their equator‐eastward propagation direction was favored by background winds at the hemisphere of origin, as determined from global model observations.