Morphology of Martian Low-Altitude Ionospheric Layer: MGS Observations

摘要

An analysis of the entire data set of 5,600 electron density profiles returned by Mars Global Surveyor's Radio Science Experiment is carried out to study the physical characteristics of Martian low-altitude plasma layer (M layer). Our analysis suggests that this layer is predominantly observed during low and moderate solar activity periods, in northern autumn. The critical ionospheric parameters (electron density and height) of this M layer are found not to show a definitive correlation with solar zenith angle. In contrast to earlier reports where meteoroid ablation was proposed to cause total electron content (TEC) enhancements, we report that the maximum contribution from this layer (TEC_M) is only about 5.5%, while the contribution is 3.7% during predicted meteor shower, suggesting that M layer occurrence does not depend upon meteor shower nor on dust storm. It is observed that the M layer occurrence increases as the Martian E region becomes prominent and well defined, suggesting that the source which causes M layer possibly leads to more pronounced E layers. Southern hemisphere profiles were found to behave differently from northern hemisphere profiles, possibly due to crustal magnetic fields. Large surges observed in Martian F1 layer peak height during consecutive occultations (~2 hr apart) are found not to show any correlation with the occurrence of M layer and are not influenced by dust storms.