This image shows two atmospheric phenomena: the white curved lines represent gravity wave clouds, while the brown areas represent dust lifted from the ground by the wind. The visible colour change in the dust-lifting event could indicate very fast winds, a phenomenon currently being studied by other members of the team. Credit: ESA/DLR/FU Berlin.
Cloud enthusiasts have a new tool to study the impressive formations in the Red Planet’s sky. A searchable database of 20 years of cloud and storm images, created by the German Aerospace Center (DLR) in Berlin, is helping scientists better understand how and where the features appear in the Martian atmosphere and what they can tell us about the climate on Mars and other planets.
The publicly available “Cloud Atlas” of Mars was presented this week at the Europlanet Science Congress (EPSC) 2024 in Berlin by Daniela Tirsch from DLR.
The Cloud Atlas images were captured by the High Resolution Stereo Camera (HRSC) instrument, which has been in orbit aboard the European Space Agency’s (ESA) Mars Express spacecraft since 2005. Although Mars has a very thin atmosphere, many cloud formations and dust storm phenomena can develop from water ice crystals and carbon dioxide as well as dust particles.
“Clouds on Mars are just as diverse and fascinating as those we see in our skies on Earth, with some features unique to the Red Planet. One of my favorite phenomena is the magnificent ‘cloud street’, the linear rows of fluffy clouds that develop around the enormous Tharsis volcanic rise and northern lowlands in spring and summer. Although they look like cumulus clouds on Earth, they form under different atmospheric conditions,” said Dr. Tirsch. “We also see impressive dust clouds that can extend hundreds of kilometers, a phenomenon we fortunately do not experience on Earth.”
This elongated cloud formed as a result of the wind meeting the Arsia Mons mountains. It forms almost every day during a given season, from early morning until midday. Credit: ESA/DLR/FU Berlin/A. Cowart.
Dust plays a major role in the atmosphere and climate of Mars. Rare upwelling events can leave beige, dust-laden clumps suspended in the atmosphere. Large differences in temperature and atmospheric pressure during certain seasons can cause stronger-than-usual winds to lift large amounts of dust from the Martian surface. Dust clouds that spread from the tops of giant volcanoes take on the appearance of eruption clouds, although they are no longer active.
Every year, large spiral dust storms and cyclonic systems can also be observed near the Martian north pole. Studying these phenomena is essential for scientists to understand the atmosphere and circulation of air masses on Mars.
Undulating “gravity clouds” are one of the most common formations on Mars and Earth. They are observed at mid-latitudes in winter in both hemispheres, as well as over the Tharsis volcanic plateau in the southern winter. Lee waves, a special type of gravity cloud, can form on the leeward side of ridges, mountains, and other obstacles to create repeating ridge formations.
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An example of cloud streets over Vastitas Borealis, a vast area near the North Pole that is virtually devoid of craters. Credit: ESA/DLR/FU Berlin/A. Cowart
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Lee waves are a special type of cloud created by wind hitting obstacles and forming on the “leeward” or “downwind” side. The geometry of lee waves depends on the shape of the obstacles. Credit: ESA/DLR/FU Berlin.
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Lee waves are a special type of cloud created by wind hitting obstacles and forming on the “leeward” or “downwind” side. The geometry of lee waves depends on the shape of the obstacles. Credit: ESA/DLR/FU Berlin.
Some types of clouds studied are specific to locations and seasons; others, such as “twilight clouds,” can appear early in the morning at any location or at any time of year.
The HRSC Cloud Atlas will provide valuable information about the physical nature and appearance of clouds and storms, when they occur, and where they occur. This knowledge will help us understand atmospheric dynamics and climate cycles on Mars, as well as inform climate studies on other planets such as Earth and Venus. The DLR team has already used the database to create global maps showing the presence of various cloud types by season and location.
“ESA has extended the Mars Express mission until at least 2026, which will allow us to continue to fill this database and further refine our understanding of the Martian atmosphere,” said Dr Tirsch. Papers on the database and scientific applications are currently in preparation.
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