May 9, 2013
Martian Snowstorms Can Be Forecast Weeks Before They Occur
April Flowers for redOrbit.com - Your Universe Online
A new study from an international group of researchers led by the Max Planck Institute for Solar System Research (MPS) reveals that snowstorms that lash the northern hemisphere of Mars during the harsh winters may be predicted several weeks in advance.
Similar to those on Earth, the Martian polar regions are an icy, cold world covered by cohesive ice caps. When temperatures in winter drop below -198.4 degrees Fahrenheit — the point at which carbon dioxide freezes — this ice layer is supplied by frozen co2 from the atmosphere. The ice caps cover a region reaching south to about 70 degrees northern latitude during the winter. During the Martian summer, which is comparatively warmer, the carbon dioxide sublimates to reveal the planet´s eternal ice. This cap is considerably smaller than the winter ice caps.
“Mars' seasonal ice has two different origins“, says Dr. Paul Hartogh from the MPS. “A part of the carbon dioxide from the atmosphere condensates directly on the surface — similar to the way a layer of frost forms on Earth in cold, clear weather. Another part freezes in the atmosphere.”
The co2 that freezes in the atmosphere forms tiny ice crystals that accumulate into clouds and then fall to the ground as snow. The new study, published in a recent issue of Geophysical Research Letters, establishes a connection between the occurrence of such ice clouds and a wave-like weather phenomenon characterized by a periodic change of pressure, temperature, wind speed, and direction for the first time.
"This weather phenomenon on Mars is unique", says Dr. Alexander Medvedev from the MPS. These so-called planetary waves can be found in Earth´s meteorology; however, the oscillations in pressure and temperature in the lower atmosphere are much weaker on Earth. The waves also occur much less regularly, and their wave characteristics are less pronounced.
"In the Martian northern hemisphere between fall and spring these waves can be found with astonishing reliability", Medvedev adds. The waves on Mars propagate eastward with a uniform period of five to six days. Waves with higher frequencies can also be observed close to the surface.
Because of planetary waves, the Martian atmosphere regularly drops below -198.4 F, allowing the co2 to crystallize and form clouds.
“These clouds can be found north of 70 degrees northern latitude in all layers of the atmosphere up to a height of [25 miles]," says Hartogh. The snowfall is a result of ice crystals that form below 12.4 miles.
"In order for such snowfalls to occur, the periodic temperature changes must be similar in all layers of the atmosphere", explains Medvedev. Below the 12.4-mile mark, this is a given. In all other cases, however, the snow crystals encounter warmer air layers and sublimate. These requirements are well fulfilled in a region of the northern hemisphere between 30 degrees western longitude and 60 degrees eastern longitude. Space telescope and space probe images show that the resulting ice cap in this region reaches especially far to the south.
The team, which includes scientists from Tohoku University in Japan, estimates that approximately half of the seasonal ice falls to the ground as snow.
The team used an established climate model for their simulations, which they adapted to the special conditions on Mars. “The calculations need to take into account the large amounts of dust in the Martian atmosphere“, says Dr. Takeshi Kuroda from Tohoku University, who worked at the MPS until 2009 where he also received his PhD.
The Martian atmosphere consists of more than 95 percent carbon dioxide, in addition to all the dust. The calculated temperatures and ice crystal densities from this study are in agreement with measured data obtained from NASA´s Mars Reconnaissance Orbiter (MRO).
The new results could help to reliably predict snowstorms on Mars, the team claims. "Everyone knows from experience that on Earth reliable weather forecasts are only possible for a time span of five to seven days at most", says Medvedev. "It is simply impossible to calculate whether or not it will snow somewhere on Earth 20 or 40 days in advance."
On Mars, according to the new study, this is different. The simulations reveal that snow fall in certain regions of Mars can be predicted far in advance. "For missions to Mars aiming to explore these regions with rovers this is valuable information", says Hartogh.