[meteorite-list] NASA Mars Orbiters Reveal Seasonal Dust Storm Pattern

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=6529

NASA Mars Orbiters Reveal Seasonal Dust Storm Pattern
Jet Propulsion Laboratory
June 9, 2016

Fast Facts:

* A pattern of three large regional dust storms occurs with similar timing 
most Martian years.

* The seasonal pattern was detected from dust storms' effects on atmospheric 
temperatures, monitored by NASA orbiters since 1997.

* Improving the ability to predict large-scale, potentially hazardous 
dust storms on Mars would have safety benefits for planning robotic and 
human missions.

After decades of research to discern seasonal patterns in Martian dust 
storms from images showing the dust, but the clearest pattern appears 
to be captured by measuring the temperature of the Red Planet's atmosphere.

For six recent Martian years, temperature records from NASA Mars orbiters 
reveal a pattern of three types of large regional dust storms occurring 
in sequence at about the same times each year during the southern hemisphere 
spring and summer. Each Martian year lasts about two Earth years.

"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 
of NASA's Jet Propulsion Laboratory, Pasadena, California. He is the instrument 
scientist for the Mars Climate Sounder on NASA's Mars Reconnaissance Orbiter 
and lead author of a report about these findings posted this week by the 
journal Geophysical Research Letters.

"Recognizing a pattern in the occurrence of regional dust storms is a 
step toward understanding the fundamental atmospheric properties controlling 
them," he said. "We still have much to learn, but this gives us a valuable 
opening."

Dust lofted by Martian winds links directly to atmospheric temperature: 
The dust absorbs sunlight, so the sun heats dusty air more than clear 
air. In some cases, this can be dramatic, with a difference of more than 
63 Fahrenheit degrees (35 Celsius degrees) between dusty air and clear 
air. This heating also affects the global wind distribution, which can 
produce downward motion that warms the air outside the dust-heated regions. 
Thus, temperature observations capture both direct and indirect effects 
of the dust storms on the atmosphere.

Improving the ability to predict large-scale, potentially hazardous dust 
storms on Mars would have safety benefits for planning robotic and human 
missions to the planet's surface. Also, by recognizing patterns and categories 
of dust storms, researchers make progress toward understanding how seasonal 
local events affect global weather in a typical Mars year.

NASA has been operating orbiters at Mars continuously since 1997. The 
Mars Climate Sounder on Mars Reconnaissance Orbiter, which reached Mars 
in 2006, and the Thermal Emission Spectrometer on Mars Global Surveyor, 
which studied Mars from 1997 to 2006, have used infrared observations 
to assess atmospheric temperature. Kass and co-authors analyzed temperature 
data representative of a broad layer centered about 16 miles (25 kilometers) 
above the Martian surface. That's high enough to be more affected by regional 
storms than by local storms.

Most Martian dust storms are localized, smaller than about 1,200 miles 
(about 2,000 kilometers) across and dissipating within a few days. Some 
become regional, affecting up to a third of the planet and persisting 
up to three weeks. A few encircle Mars, covering the southern hemisphere 
but not the whole planet. Twice since 1997, global dust storms have fully 
enshrouded Mars. The behavior of large regional dust storms in Martian 
years that include global dust storms is currently unclear, and years 
with a global storm were not included in the new analysis.

Three large regional storms, dubbed types A, B and C, all appeared in 
each of the six Martian years investigated.

Multiple small storms form sequentially near Mars' north pole in the northern 
autumn, similar to Earth's cold-season arctic storms that swing one after 
another across North America.

"On Mars, some of these break off and head farther south along favored 
tracks," Kass said. "If they cross into the southern hemisphere, where 
it is mid-spring, they get warmer and can explode into the much larger 
Type A dust storms."

Southern hemisphere spring and summer on modern-day Mars are much warmer 
than northern spring and summer, because the eccentricity of Mars' orbit 
puts the planet closest to the sun near the end of southern spring. Southern 
spring and summer have long been recognized as the dustiest part of the 
Martian year and the season of global dust storms, even though the more 
detailed pattern documented in the new report had not been previously 
described.

When a Type A storm from the north moves into southern-hemisphere spring, 
the sunlight on the dust warms the atmosphere. That energy boosts the 
speed of winds. The stronger winds lift more dust, further expanding the 
area and vertical reach of the storm.

In contrast, the Type B storm starts close to the south pole shortly before 
the beginning of southern summer. Its origin may be from winds generated 
at the edge of the retreating south-polar carbon dioxide ice cap. Multiple 
storms may contribute to a regional haze.

The Type C storm starts after the B storm ends. It originates in the north 
during northern winter (southern summer) and moves to the southern hemisphere 
like the Type A storm. From one year to another, the C storm varies more 
in strength, in terms of peak temperature and duration, than the A and 
B storms do.

The longevity of NASA's Mars Reconnaissance Orbiter has helped enable 
studies such as this of seasonal patterns on Mars. JPL provided the Mars 
Climate Sounder instrument and manages the mission for NASA's Science 
Mission Directorate. Arizona State University, Tempe, provided the Thermal 
Emission Spectrometer for Mars Global Surveyor. Lockheed Martin Space 
Systems, Denver, built both orbiters.

News Media Contact
Guy Webster
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-6278
guy.w.webster at jpl.nasa.gov

2016-146