Orographic elongated clouds in mid-temperate and subpolar latitudes of Mars. I-Observations

We report new cases of extremely long and narrow clouds, visually similar in their morphology to the Arsia Mons elongated cloud (AMEC) (Hernández-Bernal et al., 2021a, 2022), that form at mid-temperate and subpolar latitudes in both hemispheres of the planet. We focus on four regions with different topography: the rugged mountain range of Thaumasia Highlands (267°E, 40°S), the volcanic region of Alba Patera (250°E, 40°N), the fretted and cratered highland terrain Tempe Terra (285°E, 48°N), and Lyot crater (29.3°E, 50.4°N). We use the images obtained by the Visual Monitoring Camera (VMC) on board the Mars Express mission, profiting from Mars Express' advantageous polar elliptical orbit, which allows us to characterize these clouds at different local times and spatial resolutions. At the elevated region of Thaumasia Highlands clouds form throughout the southern fall and winter during Ls = 0° – 170°, with lengths of up to 2700 km, widths of up to 220 km and heights 10–22 km above the surface. The elongated clouds at Alba Patera and Tempe Terra form during the northern fall and winter seasons between Ls = 180° – 330° with maximum lengths of 2600 km and 1900 km, maximum widths of 270 km and 240 km and heights between 10 and 27 km and 8–22 km respectively. Similarly, the elongated clouds at Lyot crater form during Ls = 180° – 340° and can have lengths of up to 2600 km and widths of up to 300 km. However, their heights are lower ranging 5–16 km over the surface. • We study four cases of long and narrow orographic clouds on Mars. • They form at Thaumasia Highlands, Alba Patera, Tempe Terra and Lyot crater. • They are seasonal and develop during fall and winter in each hemisphere. • They can reach lengths of up to 2600 km with widths between 100 and 200 km. • Their heights range about 10 to 25 km over the surrounding terrain.