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

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Sat, 18 Jun 2016 21:04:21 -0700 (PDT)
Message-ID: <201606190404.u5J44Lkx014258_at_zagami.jpl.nasa.gov>

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
Received on Sun 19 Jun 2016 12:04:21 AM PDT