NASA scientists have been trying for decades to uncover seasonal patterns in the dust storms on Mars, their efforts have at last proven fruitful, but the new data that helped pave the way for their success came from a somewhat unexpected source: atmospheric temperature readings.
As the US space agency announced late last week, the researchers recently abandoned efforts to find the patterns from images showing dust grains, and instead reviewed six recent Martian years of temperature records collected by the Mars Reconnaissance Orbiter and other probes.
They discovered that there was a pattern of three types of large, regional dust storms occurring at approximately the same time during spring and summer in the planet’s southern hemisphere each year. Their findings have been published online by the journal Geophysical Research Letters.
“When we look at the temperature structure instead of the visible dust, we finally see some regularity in the large dust storms,” said David Kass from the NASA Jet Propulsion Laboratory (JPL) in Pasadena, California, instrument scientist for the MRO’s Mars Climate Sounder and the lead author of the new study.
“Recognizing a pattern in the occurrence of regional dust storms is a step toward understanding the fundamental atmospheric properties controlling them,” he continued. “We still have much to learn, but this gives us a valuable opening.”
The three types of storms (and how they were discovered)
As Kass and his colleagues explained, there is a direct link between atmospheric temperature and the dust content of Martian winds. Since dust absorbs sunlight, air filled with dust grains tends to be hotter than clear air. In some instances, the differences are extremely pronounced, with a more than 63-degree Fahrenheit (35-degree Celsius) difference in air temperature.
Additionally, this heating was found to have an impact on the global wind distribution, which is capable of producing a downward motion that warms the air beyond the dust-heated regions, the researchers noted. This enables NASA to use temperature observations to monitor both the direct and indirect effects of the dust storms on the atmosphere, which can improve the safety of future Mars missions and help predict how localized events impact global weather on the planet.
The MRO has been observing the climate on Mars since 2006, and before that, the data had been collected by the Thermal Emission Spectrometer on the Mars Global Surveyor, which studied the atmospheric temperature from 1997 through 2006. By analyzing temperature data representative of a broad layer located 16 miles (25 km) above the planet’s surface – high enough to be affected by regional storms more than by local storms – Kass and his colleagues were able to detect three different types of large regional storms, which they dubbed types A, B and C.
Type A storms, they explained, move from the north into the southern hemisphere during that part of the planet’s spring. When that happens, the sunlight on the dust warms the atmosphere, causing the winds to become stronger, lifting up more dust and further expanding the area and the vertical reach of the storm.
Conversely, Type B storms begin near the south pole shortly before the start of summer in the southern part of the planet. These storms often originate from winds generated at the edge of the retreating south-polar carbon dioxide ice cap, and may contribute to a regional haze, the authors said. Finally, Type C storms begin after Type B storms end, originating in the north during the winter season there and moving into the south similar to Type A storms. These storms are more varied in strength, peak temperature and duration than the other two, according to NASA.
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Image credit: NASA/JPL-Caltech/MSSS
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