Transient layers in the topside ionosphere of Mars

Abstract

[1] Radar soundings from the MARSIS instrument on board the Mars Express spacecraft have shown that distinct layers can occur in the topside ionosphere of Mars, well above the main photo-ionization layer. These layers appear as cusps, or sometimes steps, in plots of the time delay as a function of frequency. Usually only one topside layer is observed, typically at altitudes from 180 to 240 km. However, occasionally an additional layer occurs at even higher altitudes. The layers are transient features and are present about 60% of the time near the subsolar point, decreasing with increasing solar zenith angle to less than 5% at the terminator and the nightside. The transient nature of the layers suggests that they are produced by a dynamical process, most likely involving an interaction with the solar wind in the upper levels of the ionosphere. Citation: Kopf,

Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS) after nine years of operation: A summary

“…Finally, we note the use of the remote sounding data to detect transient upper layers in the Martian dayside ionosphere, as reported by Kopf et al (2008). These structures are short lived and appear to occur frequently during space weather events.…”

Large density fluctuations in the martian ionosphere as observed by the Mars Express radar sounder

“…However, we cannot rule out solar wind disturbances as a possible contributing source. Kopf et al, (2008) have observed transient layers in the upper ionosphere on the dayside of Mars at solar zenith angels less than about 60°that could very well be caused by such solar wind disturbance. Unfortunately, the absence of a suitable upstream monitor in the solar wind makes it very difficult to evaluate solar wind disturbances as a source.…”

Topside of the martian ionosphere near the terminator: Variations with season and solar zenith angle and implications for the origin of the transient layers

“…Based on MARSIS data, extensive investigations have been conducted by many researchers to characterize the daytime (e.g., Gurnett et al, 2005Gurnett et al, , 2008Morgan et al, 2008;Kopf et al, 2008;Nielsen et al, 2007aNielsen et al, , 2007bAkalin et al, 2010;Němec et al, 2011) and nighttime (Safaeinili et al, 2007;Gurnett et al, 2008;Němec et al, 2010) ionosphere of Mars. Current knowledge of the main ionospheric layer of Mars (called M2) that have been achieved by using observations from various instruments, including MARSIS, can be found in a review by Withers (2009).…”

“…Beside the SZA, many factors affect the martian ionosphere to various degrees. For example, seasonal atmospheric actions (e.g., Zou et al 2005;Morgan et al 2008), the crustal magnetic field (e.g., Krymskii et al, 2003;Lillis et al, 2008;, the martian longitude (related to tides in the atmosphere that influence the ionosphere) (e.g., Bougher et al, 2004;Breus et al, 2004), the martian ground surface topography (related to wind patterns on Mars Wang and Nielsen, 2004), Mars rotation (Shinagawa, 2000), solar rotation (related to periods of relatively high and low solar fluxes) , distance from Mars to the Sun (related to the strength of solar radiation e.g., Breus et al, 2004;Morgan et al, 2008;Němec et al 2011), and the solar wind (induces magnetic fields and interacts with the topside of the ionosphere) (e.g., Wang and Nielsen, 2003a;Kopf et al, 2008;Dubinin et al, 2008). Near the terminator, the ionosphere has a sparser plasma density, higher altitude and stronger variability in the profile shape than the ionosphere far from the terminator in the daytime (e.g., Gurnett et al, 2005Gurnett et al, , 2008Morgan et al, 2008;Withers, 2009;Němec et al, 2011).…”