Mars lower atmosphere - Some new implications.

Based on occultation data from the Mariner spacecraft, there are some preliminary indications of an apparent systematically higher surface pressure on the night side of Mars than on the day side. If confirmed by additional data currently becoming available, this apparent surface pressure difference could be attributed to several causes, including topography effects as has been assumed previously, an actual increase of pressure on the night side caused by diurnal effects, an apparent increase on the night side due to some mechanisms such as a dust layer, or an apparent lower pressure on the day side due to the existence of a low-lying electron layer. By calculating the effect of a low-lying electron layer on the combined neutral atmosphere and electron layer refractivity profile, it is found that the day side and night side surface pressures would be in agreement if a layer with maximum density of about 80,000 electrons per cu cm below 15 km altitude were present on the day side.