The Analysis of the Topside Additional Layer of Martian Ionosphere Using MARSIS/Mars Express Data

Abstract

In this study, the transient second or third layer on the topside of the Martian ionosphere were investigated with the most recently released Mars advanced radar for subsurface and ionospheric sounding/Mars Express data obtained from January 2010 to September 2011 to study the correlation between these topside additional layers and surface magnetic fields, solar zenith angle and solar activities. When examining the zones where the topside layer appeared, the occurrence rate of the topside layer was low at the areas with a strong Martian crustal magnetic field as observed by the Mars global surveyor. The occurrence rate of additional layers on the Martian topside ionosphere decreases as the solar zenith angle increases. However, these layers appeared significantly near the terminator of which solar zenith angle is 90°. In comparison between F10.7 which is the index of solar activities and the occurrence rate of the topside layer by date, its occurrence rate was higher in 2011 than in 2010 with less solar activities. The result of this study will contribute to better understanding of the environments in the topside of the ionosphere through the correlation between the various conditions regarding the Martian ionosphere and the transient layer.

The transient topside layer and associated current sheet in the ionosphere of Mars

“…The initial results reported by Kopf et al [] noted that these layers appeared all over the planet, including in the significantly less magnetized northern hemisphere. More recently it was demonstrated that the layer was almost exclusively present away from the main magnetism regions in the Southern Hemisphere, and especially common in the low‐magnetism regions [ Kim et al , ], a finding backed up by this study, which found the bulk of these layer detections to be in the Northern Hemisphere or near the equator, with less than a handful anywhere near the strong southern crustal field regions. This finding combined with those by Harada et al [] makes it possible that these are magnetized plasma parcels downstream from a more subsolar reconnection point.…”

“…This magnetism has been mapped all across the surface of the planet [ Connerney et al , ], and various spherical harmonic models have been devised to compute its components and strengths [e.g., Cain et al , ; Arkani‐Hamed , ]. Although Kopf et al [] found no direct correlation between the crustal fields and the detection of the second layer, a result supported by a significantly larger study [ Kim et al , ], the limited time range and indirect nature of that early study left room for the possibility of a connection on a broader scale.…”

“…If reconnection is indeed the cause of this transient layer, then it is in reality more of a localized phenomenon than an actual layer. However, a current sheet alone does not directly imply reconnection, and it is unclear what processes would drive it at this altitude to form this layer, especially given the layer's tendency for appearing away from crustal magnetic field features [ Kim et al , ].…”

Shapes of Magnetically Controlled Electron Density Structures in the Dayside Martian Ionosphere

“…Kopf et al () have discovered the existence of transient topside layers above the main ionospheric peak, at typical altitudes 180–240 km on the dayside, with an occurrence rate decreasing when going from the subsolar region to the terminator (from 60% to 5% of observation time). The topside layers are found mostly in regions of low crustal magnetic field strength (e.g., Kim et al, ; Kopf et al, ). It is not known whether topside layers exist in regions of stronger crustal fields, because the presence of electron cyclotron harmonics in the ionograms can hinder the visibility of the ionospheric traces at low frequency, including any potential topside layer.…”

Ionospheric Electron Densities at Mars: Comparison of Mars Express Ionospheric Sounding and MAVEN Local Measurements

“…As a consequence, the inversion process is not unambiguous, and a unique solution is found by assuming a predefined electron density profile shape in the return signal gap region (Němec, Morgan, Gurnett, ). The electron densities are generally assumed to monotonically increase with decreasing altitude down to the altitude of the peak; that is, any density voids in the altitude profile/transient layers (Kim et al, ; Kopf et al, ; Withers, Fillingim, et al, ) cannot be evaluated.…”