Starting in September 2018, a daily repeating extremely elongated cloud was observed
extending up to 1800km 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, MCC on Mars Orbiter Mission (MOM), MARCI on MRO,
and Visible Camera on Viking 2 orbiter. We study the daily cycle of this cloud, showing
how the morphology and other parameters of the cloud evolved rapidly with local time.
The cloud expands every morning from the western slope of the volcano, at a westward
velocity of around 160m/s, and an altitude of around 45km over martian areoid. The
expansion starts with sunrise, and resumes around 2.5 hours later, when cloud formationresumes and the elongated tail detaches from the volcano and keeps moving westward
until it evaporates before afternoon, when most sun-synchronous missions observe. This
daily cycle repeated regularly for at least 80 sols in 2018 (Martian Year 34). We find in
images from past years that this AMEC is an annually repeating phenomenon that takes
place around the Solar Longitude range 220º-320º. We study the AMEC in Martian Year
34 in terms of Local Time and Solar Longitude, and then compare with observations from
previous years, in search for interannual variations, taking into account the possible
influence of the recent Global Dust Storm
