Solar rotation effects on the Martian ionosphere

Abstract

We present a detailed investigation of the solar rotation effects on the Martian high-latitude (~63°N-81°N) ionosphere using the electron density (N e ) data measured by Mars Global Surveyor and solar XUV and EUV fluxes measured by SOHO under high (2000SOHO under high ( -2001SOHO under high ( ), medium (2003, and low (2005) solar activity conditions. A fast Fourier transform spectral analysis method is used to estimate the amplitude of the rotation period in these parameters. This method clearly reveals the presence of solar rotation effects in the Martian ionospheric N e at all altitudes (90-220 km), peak electron density (N m M2), and total electron content under the three solar activity conditions. These effects are in phase with the solar UV fluxes (corrected for the Martian orbit). The period of rotation effect (~26 days) is the same at all altitudes, though its amplitude is strongest at the ionospheric M2 peak (~135-140 km,~3.5-6% of the mean values) and has a secondary enhancement at the M1 peak (~110-115 km). The effect of solar rotation on the M2 peak is larger during medium solar activity (2003) than during high solar activity (2000)(2001). The effect, however, is absent in the ionospheric peak height (h m M2). The rotation effects on Mars are also compared with those on the Earth. Unlike at Mars, the Earth's high-latitude ionosphere shows no clear solar rotation effect, though the effect is observed clearly at lower latitudes.

Effects of Local Dust Storms on the Upper Atmosphere of Mars: Observations and Simulations

“…For comparison, 10 profiles observed on 2 January 2005 when ionospheric main peak heights reach the maximum were selected to show the status of the Martian ionosphere at the peak of the abnormal event; these are referred to as "Storm Day" profiles. To show the status of the Martian ionosphere clearly, the electron density profiles are averaged to get a daily mean profile with the method used in the previous study (Venkateswara Rao et al, 2015). Figure 4 shows the daily mean profiles on Start Day or called Pre-storm Day (dash-dot line) and Peak Day or called Storm Day (solid line) between 100 and 180 km with 1-km height resolution.…”

Mars Global Ionosphere‐Thermosphere Model: Solar cycle, seasonal, and diurnal variations of the Mars upper atmosphere

“…These temporal variations result from the changing heliocentric distance (∼1.38–1.67 AU), the planet's obliquity (determining the local season), and the changing solar radiation itself. Both solar rotation (∼27 day periodic changes in the solar output) and solar cycle (∼11 year periodic overall changes in solar output) variations of the solar X‐ray and EUV fluxes are significant (up to factors of ∼3 to 100, depending on the wavelength [ Woods and Rottman , ]), producing dramatic variations in global thermospheric temperatures, composition, and winds [e.g., Bougher et al , ; Forbes et al , ], as well as ionospheric densities [e.g., Fox , ; Venkateswara Rao et al , ]. Thus, significant variability of the Martian thermosphere and ionosphere system is directly linked to the variability of the solar EUV‐UV fluxes received at Mars.…”

Characterizing Average Electron Densities in the Martian Dayside Upper Ionosphere

“…The ionosphere of Mars is known to exhibit periodicities related to the solar rotation (Nielsen et al, 2006;Rao et al, 2014), and its variability as a function of the solar cycle was also reported (Sánchez-Cano et al, 2015;Withers, Vogt, et al, 2015). Crustal magnetic fields can also influence the electron densities, in particular at high altitudes (Andrews et al, 2014;Němec, Morgan, Gurnett, & Andrews, 2016).…”