Mid-latitude F-region studies based on ISS-B and DE-2 observations

Mid-latitude topside ionograms from the ISS-B satellite display range and frequency spreading which we collectively call Topside Spread Echoes (TSEs). These TSEs show marked seasonal and longitudinal dependence. The north Atlantic region has the highest occurrence probability in the winter solstice. The smallest occurrence is in the north Pacific in the same interval. Occurrence probabilities of up to about 30% are quite common.; The spread echoes are divided into two types and found to have different geophysical dependences. Small-scale events have a strong seasonal dependence on magnetic declination and do not have an obvious correlation with auroral indices. Large-scale events have no observed dependence on magnetic declination, but are anticorrelated to the auroral electrojet (AE) index 6-8 hours prior to their appearance [Earle et al., 2006]. The correlation of larger scale events with reduced AE values rules out traveling ionospheric disturbances (TIDS) from aurora as the most likely cause of the large scale spread echoes.; A separate in-situ study using Dynamics Explorer 2 (DE-2) data looks at bottomside traveling ionospheric disturbances. The study identifies ionospheric perturbations in the ion concentration. Distinct waves are observed in four passes of the Dynamics Explorer 2 satellite in the southern mid-latitude hemisphere between 250 and 300 km. The source of the wave-like perturbations is determined to be gravity-wave induced dynamics and chemistry in the neutral atmosphere. The periods of the gravity waves are ∼30 minutes, consistent with results from numerical studies of gravity wave propagation from lower atmospheric and thermospheric sources [Vadas, 2007].