A Seasonally Recurrent Annular Cyclone in Mars Northern Latitudes and Observations of a Companion Vortex

Abstract

We study a seasonally recurrent cyclone and related cloud phenomena observed on Mars at L s 120°, latitude~60°N, and longitude 90°W from images obtained with cameras in different spacecraft between 1995 and 2018. A remarkable double cyclone formed in 2012 and we present a detailed study of its dynamics using images from Mars Express and Mars Reconnaissance Orbiter obtained between 6 June and 9 July. A double cyclone was also observed in 2006 and 2008. In other Martian years the primary cyclone showed an annular cloud morphology with a large water ice cloud observed eastward of it. The cyclones have a size of~600-800 km with a cloud-free core of a radius~100-300 km. Tangential velocities measured from cloud tracking in 2012 images are~5-20 m/s À1 at 10-km altitude and double cyclone moved eastward with a velocity of 4 m/s À1 during its lifetime of one month. The vortices grow in the morning hours, but with the increasing insolation as the sol progresses, a part of the clouds evaporate, the winds weaken, and the vortices lose coherence. This phenomenon forms under high-temperature gradients in a region with a large north-south topographic slope and has been recurrent each Martian year between 1995 and 2018. We argue the interest of studying its changing properties each Martian year in order to explore their possible relationship to the state of the Martian atmosphere at L s~1 20°. Plain Language SummaryWe study a remarkable annular vortex observed some years to be formed by two coupled cyclones that grow every Martian northern summer at the same longitude and latitude of the planet. Each vortex has a size of 700 km and its center is a cloud-free area with a radius of about 200 km. The vortex is formed by water ice clouds at about 10-km altitude where the winds blow with speeds of 5 to 20 m/s. The clouds grow in the morning hours and sublimate as the vortex weakens with increasing insolation. Dynamical models show that the vortex forms in a region with a large north-south terrain slope that combines with north-south temperature gradient. The study mainly uses images taken in 2012, but a survey shows that the vortex recurrently forms every Martian year between 1995 and 2018. This vortex system can be used as a proxy, studying its variability, to characterize the state of the atmosphere at the time of its formation.

Dynamics of the extremely elongated cloud on Mars Arsia Mons volcano

“…We study the phenomenon across several years, in search for variations in its Ls range, or any other measurable parameters. This phenomenon might hold the added value of being useful as a proxy for interannual variations in the atmosphere, similar to an already studied cyclone also observed by VMC and other instruments [3].…”

“…The season before the Martian southern solstice is known for the general lack of water ice clouds on the planet, however, 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 2018 Martian Global Dust Storm Over the South Polar Region Studied With MEx/VMC

“…Here we use VMC images to track motions of the dust during the 2018 dust storm (Figure ). Previous wind measurements associated to cloud features using VMC images can be found in Sánchez‐Lavega, Garro, et al (). We have measured 10 pairs of VMC images taken between 1 July and 3 August separated by 20–40 min at a spatial resolution of ~11 km/pixel that allows us to retrieve velocities with an estimated error of 10 m/s.…”

Mars Reconnaissance Orbiter's Mars Color Imager (MARCI): A New Workflow for Processing Its Image Data

“…Those swaths built a nearly global view, every Mars day, at an approximately consistent time (early afternoon) and consistent pixel scales of ∼6.5 km/pix. Four years after MGS 's science mission began, ESA's Mars Express ( MEx ) arrived, providing images with its engineering VIsual monitoring Camera (VIC; Ormston et al., 2011; Sánchez‐Lavega et al., 2018) and science High‐Resolution Stereo Camera (HRSC; Jaumann et al., 2007). VIC is a low‐resolution RGB (red‐green‐blue) camera and takes images at apoapsis, and HRSC is a blue, green, far‐red, and near‐IR (∼1 μm) camera.…”