Longitudinal Characteristics of Martian Electron Density Profiles: MGS Observations

An analysis of longitudinal characteristics of 5,600 electron density profiles returned from the Mars Global Surveyor's Radio Science experiment is carried out by dividing the entire data set into 33 subsets, keeping solar zenith angle nearly constant. We find that the peak altitude of the photochemical F1 layer (hmF1) exhibits a large degree of longitudinal variability. This variability is not seen in Earth's ionosphere. Since F1 layer is isobaric, this variability in hmF1 represents a large degree of spatial changes in the underlying neutral atmosphere. Though this variability is quite chaotic in most of the subsets, a few subsets provide some evidence for the presence of a well-defined wave. We therefore perform a spectral fit of wave 1-3, as earlier carried out by Bougher et al. (2004, https://doi.org/10.1029/2003JE002154; 2001, https://doi.org/10.1029/2001GL012884), to all 33 subsets. Results indicate that this wave is seen only in 10 of the subsets and is most dominant between 0 to 200 degrees E longitudes. Similar wave is seen in the longitude plots of the peak electron density of F1 layer but with a phase reversal. Further, these 10 subsets are confined mostly between 02 to 04 local solar time, thereby indicating a local time dependence of the wave. We examined the characteristics of electron density profiles located at the crests and troughs and found abnormal upliftment in F1 layer during consecutive occultations (similar to 2 hr). Rapid spatial changes are observed during intervals as short as 2 hr. The ionosphere is lifted up and the peak density decreases when wave 1-3 is present.