In Situ Observation of Solar-flare-induced Proton Cyclotron Waves Upstream from Mars

Abstract

Proton cyclotron waves (PCWs) upstream from Mars are usually interpreted as waves generated by ion/ion instabilities due to the interaction between the solar wind plasma and the pickup protons, originating from the extended hydrogen (H) exosphere of Mars. Their generation mainly depends on the solar wind properties and the relative density of the newborn protons with respect to the background solar wind. Under stable solar wind conditions, a higher solar irradiance leads to both increased exospheric H density and ionization rate of H atoms, and therefore a higher relative density, which tends to increase the linear wave growth rate. Here we show that the solar irradiance is likely to contribute significantly to PCW generation. Specifically, we present observations from the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft indicating that, around the peak of the X8.2 flare on 2017 September 10, the increased solar irradiance gave rise to higher pickup H+ fluxes, which in turn excited PCWs. This result has implications for inferring the loss of hydrogen to space in early Martian history with more intense and frequent X-class flares as well as their contributions to the total loss.

Upstream Proton Cyclotron Waves at Mars During the Passage of ICMEs

“…We examine the solar irradiance in three broad wavelength bands (0.1–7 nm, 17–22 nm, and 121–122 nm) detected at Mars by MAVEN/EUVM (Eparvier et al., 2015) and the Martian dust storm activity (cf. Figure 1 of Fang et al., 2020), and find that they did not undergo any intrinsic changes during individual ICMEs (on timescales up to a few days), and therefore would not necessarily result in an enhancement of H abundance in the extended corona (Chaufray et al., 2015; Jakosky et al., 2018; Lin et al., 2022). Subsequently, two possible scenarios come to mind.…”

“…It is worth noticing that some waves detected by MAVEN might be generated further upstream in the solar wind (i.e., they were being convected back by the solar wind). These waves might have already evolved a lot from the linear phase, and thus they do not appear as nearly monochromatic waves (e.g., Lin et al., 2022). In such case, the connection between the wave amplitudes and the exospheric H density can be much more complicated requiring a non‐linear scenario (Mazelle et al., 2004).…”

“…It was launched in November 2013, and was inserted into orbit around Mars in September 2014. It operates in a precessing 4.5-hr elliptical orbit with a periapsis altitude of 150 km and an apoapsis altitude of ∼6,400 km, and provides simultaneous plasma and magnetic field measurements, allowing for the examination of low-frequency plasma waves in the medium upstream from the Martian BS (e.g., Andrés et al, 2020;Halekas et al, 2020;Lin et al, 2022;Romanelli et al, 2016;Romeo et al, 2021;Ruhunusiri et al, 2016). More recently, Zhao et al (2021) identified 24 ICMEs using the MAVEN measurements from October 2014 to February 2019, covering the declining phase of solar cycle 24 from a near solar maximum to a near solar minimum condition.…”

“…The first detection of PCWs at Mars was analyzed by Russell et al (1990) with data from the MAGMA magnetometer onboard Phobos 2 spacecraft. Since then, PCW occurrence, wave properties and favorable generation conditions have been widely investigated both experimentally and theoretically (Bertucci et al, 2013;Brain et al, 2002;Lin et al, 2022;Mazelle et al, 2004;Romanelli et al, 2013Romanelli et al, , 2016Romeo et al, 2021;Ruhunusiri et al, 2015Ruhunusiri et al, , 2016Wei & Russell, 2006;Wei et al, 2011Wei et al, , 2014. Now it is well known that PCWs are left-handed polarized in the spacecraft frame and propagate in a direction quasi-parallel to the ambient magnetic field.…”

Upstream proton cyclotron waves at Mars during the passage of solar wind stream interaction regions

“…Since the first detection of PCWs at Mars by the MAGMA magnetometer on board the Phobos-2 spacecraft in 1989 (Russell et al 1990), their specific properties, generation mechanisms, and generation conditions have received considerable attention from theoretical and experimental points of view (Brain et al 2002;Mazelle et al 2004;Wei & Russell 2006;Wei et al 2011Wei et al , 2014Bertucci et al 2013;Romanelli et al 2013Romanelli et al , 2016Ruhunusiri et al 2015Ruhunusiri et al , 2016Romeo et al 2021;Lin et al 2022). It is now widely known that PCWs are LH polarized in the spacecraft frame and propagate nearly parallel to the background magnetic field direction.…”