Global Distribution of Nighttime MSTIDs and Its Association With E Region Irregularities Seen by CHAMP Satellite

We investigate the correlation of sporadic E (Es) with the occurrence of medium‐scale traveling ionospheric disturbances (MSTIDs) at night in middle latitudes (25°–40°N and 25°–40°S magnetic latitudes) by examining their occurrence climatology. The occurrence climatology of Es and MSTIDs is derived using the Challenging Minisatellite Payload satellite data acquired in 2001–2008 and 2001–2009, respectively. Electron density irregularities and radio scintillations are used as the detection proxies of MSTIDs and Es, respectively. The occurrence rate of MSTIDs shows a semi‐annual variation with the primary peak during June solstices and the secondary peak during December solstices in both hemispheres. However, the occurrence rate of Es shows a seasonal variation with a pronounced peak in summer in both hemispheres. The occurrence of MSTIDs during local summer and equinoxes is correlated with the occurrence of local Es, but the high occurrence rate of MSTIDs in local winter is not correlated with local winter hemisphere Es. MSTIDs in the winter hemisphere are correlated with magnetically conjugate MSTIDs in the summer hemisphere; these summer hemisphere MSTIDs are correlated with the occurrence of Es in the summer hemisphere. The occurrence rate of MSTIDs clearly shows an increase with decreasing solar activity, but the solar cycle dependence of Es is not obvious from the data. This observation suggests that the generation of MSTIDs is significantly affected by factors other than Es such as the growth rate of the Perkins instability, atmospheric gravity waves, and the F region conductance. Key Points Nighttime medium‐scale traveling ionospheric disturbances (MSTIDs) in summer and equinoxes are correlated with sporadic E in the local hemisphere Winter hemisphere MSTIDs can be explained by summer hemisphere sporadic E The role of sporadic E in winter is contingent upon the conjugacy of MSTIDs