Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano

Jorge Hernandez Bernal,Daniela Tirsch,Nick Schneider,Iñaki Ordóñez-Etxeberria,Agustín Sánchez-Lavega,Dmitrij Titov,Kyle Connour,Ralf Jaumann,Simon Wood,Teresa Del Río-Gaztelurrutia,Ernst Hauber,Alejandro Cardesín-Moinelo,Brigitte Gondet,Eleni Ravanis,Ricardo Hueso

doi:10.5194/egusphere-egu2020-433

Abstract

&lt;p&gt;Starting in September 2018, a daily repeating extremely elongated cloud was observed extending from the Mars Arsia Mons volcano. We study this Arsia Mons Elongated Cloud (AMEC) using images from VMC, HRSC, and OMEGA on board Mars Express, IUVS on MAVEN, and MARCI on MRO. We study the daily cycle of this cloud, showing how the morphology and other parameters of the cloud evolved with local time. The cloud expands every morning from the western slope of the volcano, at a westward velocity of around 150m/s, and an altitude of around 30-40km over the local surface. Starting around 2.5 hours after sunrise (8.2 Local True Solar Time, LTST), the formation of the cloud resumes, and the existing cloud keeps moving westward, so it detaches from the volcano, until it evaporates in the following hours. At this time, the cloud has expanded to a length of around 1500km. Short time later, a new local cloud appears on the western slope of the volcano, starting around 9.5 LTST, and grows during the morning.&lt;/p&gt;&lt;p&gt;This daily cycle repeated regularly for at least 90 sols in 2018, around Southern Solstice (Ls 240-300) in Martian Year (MY) 34. According with these and previous &amp;#160;MEx/VMC observations, this elongated cloud is a seasonal phenomenon occurring around Southern Solstice every Martian Year. We study the interannual variability of this cloud, the influence of the Global Dust Storms in 2018 on the cloud&amp;#8217;s properties (S&amp;#225;nchez-Lavega et al., Geophys. Res. Lett. 46, 2019), and its validity as a proxy for the global state of the Martian atmosphere (S&amp;#225;nchez-Lavega et al., J. Geophys. Res., 123, 3020, 2018). We discuss the physical mechanisms behind the formation of this peculiar cloud in Mars.&lt;/p&gt;

Highlights

Starting on 13 September 2018, an extremely elongated cloud rising from the Arsia Mons volcano was spotted during at least 80 sols by the VMC camera onboard Mars Express [1]
A similar cloud was found in the VMC archive in different Martian Years (MY), around the southern solstice (Ls 270o), a season known for a general lack of clouds in the planet [2]
We study the behavior of this singular cloud depending on the local time, the interannual variations in its apparition every Martian year, and its possible value as a proxy for studying interannual variations in the climate of Mars

Summary

Introduction

The season before the Martian southern solstice is known for the general lack of water ice clouds on the planet, the Arsia Mons volcano seems to be an exception to this, as orographic clouds appear around it in this season [2]. The VMC camera onboard Mars Express is an engineering camera upgraded to science instrument [1] that mostly takes low resolution full-disk images of Mars, providing coverage of large areas of the planet at a wide range of local times [3, 4] This particular coverage enabled VMC to reveal an impressive elongated cloud since September 2018, which is before the southern solstice, and following the decline of the GDS 2018 [5], appearing at the western slope of the Arsia Mons volcano in the sunrise, and reaching more than 1500 km in length during the following hours. The cloud appeared everyday during at least 80 sols in Martian Year 34 (2018), and was observed by VMC, HRSC,

The dataset

Behavior with local time

Interannual variations