[meteorite-list] Mars Water-Ice Clouds Are Key to Odd Thermal Rhythm (MRO)

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Wed, 12 Jun 2013 13:13:53 -0700 (PDT)
Message-ID: <201306122013.r5CKDrvo008992_at_zagami.jpl.nasa.gov>

http://www.jpl.nasa.gov/news/news.php?release=2013-201

Mars Water-Ice Clouds Are Key to Odd Thermal Rhythm
Jet Propulsion Laboratory
June 12, 2013

PASADENA, Calif. -- Researchers using NASA's Mars Reconnaissance Orbiter
have found that temperatures in the Martian atmosphere regularly rise
and fall not just once each day, but twice.

"We see a temperature maximum in the middle of the day, but we also see
a temperature maximum a little after midnight," said Armin Kleinboehl of
NASA's Jet Propulsion Laboratory in Pasadena, Calif., who is the lead
author of a new report on these findings.

Temperatures swing by as much as 58 degrees Fahrenheit (32 kelvins) in
this odd, twice-a-day pattern, as detected by the orbiter's Mars Climate
Sounder instrument.

The new set of Mars Climate Sounder observations sampled a range of
times of day and night all over Mars. The observations found that the
pattern is dominant globally and year-round. The report is being
published in the journal Geophysical Research Letters.

Global oscillations of wind, temperature and pressure repeating each day
or fraction of a day are called atmospheric tides. In contrast to ocean
tides, they are driven by variation in heating between day and night.
Earth has atmospheric tides, too, but the ones on Earth produce little
temperature difference in the lower atmosphere away from the ground. On
Mars, which has only about one percent as much atmosphere as Earth, they
dominate short-term temperature variations throughout the atmosphere.

Tides that go up and down once per day are called "diurnal." The
twice-a-day ones are called "semi-diurnal." The semi-diurnal pattern on
Mars was first seen in the 1970s, but until now it had been thought to
appear just in dusty seasons, related to sunlight warming dust in the
atmosphere.

"We were surprised to find this strong twice-a-day structure in the
temperatures of the non-dusty Mars atmosphere," Kleinboehl said. "While
the diurnal tide as a dominant temperature response to the day-night
cycle of solar heating on Mars has been known for decades, the discovery
of a persistent semi-diurnal response even outside of major dust storms
was quite unexpected, and caused us to wonder what drove this response."

He and his four co-authors found the answer in the water-ice clouds of
Mars. The Martian atmosphere has water-ice clouds for most of the year.
Clouds in the equatorial region between about 6 to 19 miles (10 to 30
kilometers) above the surface of Mars absorb infrared light emitted from
the surface during daytime. These are relatively transparent clouds,
like thin cirrus clouds on Earth. Still, the absorption by these clouds
is enough to heat the middle atmosphere each day. The observed
semi-diurnal temperature pattern, with its maximum temperature swings
occurring away from the tropics, was also unexpected, but has been
replicated in Mars climate models when the radiative effects of
water-ice clouds are included.

"We think of Mars as a cold and dry world with little water, but there
is actually more water vapor in the Martian atmosphere than in the upper
layers of Earth's atmosphere," Kleinboehl said. "Water-ice clouds have
been known to form in regions of cold temperatures, but the feedback of
these clouds on the Mars temperature structure had not been appreciated.
We know now that we will have to consider the cloud structure if we want
to understand the Martian atmosphere. This is comparable to scientific
studies concerning Earth's atmosphere, where we have to better
understand clouds to estimate their influence on climate."

JPL, a division of the California Institute of Technology in Pasadena,
provided the Mars Climate Sounder instrument and manages the Mars
Reconnaissance Orbiter project for NASA's Science Mission Directorate,
Washington.

For more about the Mars Reconnaissance Orbiter, visit:
http://www.nasa.gov/mro .

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

Dwayne Brown 202-358-1726
NASA Headquarters, Washington
dwayne.c.brown at nasa.gov

2013-201
Received on Wed 12 Jun 2013 04:13:53 PM PDT