Climatology of Nighttime Medium‐Scale Traveling Ionospheric Disturbances at Mid and Low Latitudes Observed by the DEMETER Satellite in the Topside Ionosphere During the Period 2005–2010

Thermal ion measurements from the French Detection of Electro-Magnetic Emissions Transmitted from Earthquake Regions micro-satellite have been used to study the climatology of nighttime Medium-scale traveling ionospheric disturbances (MSTIDs) in the topside ionosphere at 650 km altitude during the 6 years of the satellite operation, from 2005 to 2010. This period encompasses the declining phase of solar cycle 23, the deep solar minimum of 2008-2009 and the early rise of solar cycle 24. MSTIDs were detected from the quasi-periodic variations of the density of the dominant ionospheric O+ ions. Mostly present between similar to 15 degrees and similar to 40 degrees invariant latitudes with a small number of events in equatorial regions, the MSTIDs exhibit, on the average, larger occurrence rates in the Southern hemisphere with a peak in the Eastern Pacific-South America longitude sector. The dependence of MSTID activity on solar activity appears more complex than the previously reported simple anti-correlation. In addition to year-to-year variations, our study has, in particular, put in evidence a noticeable hemispheric asymmetry in the seasonal variations during the deep solar minimum of 2008-2009. These statistical observations provide a remarkable observational support to the key role of sporadic Es layers and the conjugate mapping of the associated electric fields. Yet, improved theoretical and numerical models, taking into account the actual inter-hemispheric differences of the seasonal and solar activity variations of thermospheric and ionospheric processes, are needed for a better understanding of the highly complex MSTID phenomena.