WASHINGTON -- A NASA
satellite has captured the first occurrence this summer of mysterious
iridescent polar clouds that form 50 miles above Earth's surface.
The first observations of these clouds by the Aeronomy of Ice in the
Mesosphere (AIM) satellite occurred above 70 degrees north on May 25.
Observers on the ground began seeing the clouds on June 6 over northern
Europe. AIM is the first satellite mission dedicated to the study of these
These mystifying clouds are called Polar Mesospheric Clouds, or PMCs, when
they are viewed from space and referred to as "night-shining" clouds, or
noctilucent clouds, when viewed by observers on Earth. The clouds form
during the Northern Hemisphere's summer season that begins in mid-May and
extends through the end of August. They are being seen by AIM's
instruments more frequently as the season progresses. The clouds also are
seen in the high latitudes of the Southern Hemisphere during the summer
Very little is known about how these clouds form over the poles, why they
are being seen more frequently and at lower latitudes than ever before, or
why they have been growing brighter. AIM will observe two complete polar
mesospheric cloud seasons over both poles, documenting for the first time
the entire, complex life cycle of PMCs.
"It is clear that PMCs are changing, a sign that a distant and rarified
part of our atmosphere is being altered, and we do not understand how, why
or what it means," stated AIM principal investigator James Russell III,
Hampton University, Hampton, Va. "These observations suggest a connection
with global change in the lower atmosphere and could represent an early
warning that our Earth's environment is being altered."
The AIM instruments are returning valuable information on the global
extent and variability of these clouds and preliminary information on
their particle sizes and shapes. Early indications are that the clouds
occur at high latitudes early in the season then move to lower latitudes
as time progresses. The AIM science team is studying these new data to
understand whether the changes in the clouds may be related to global
When the Northern Hemisphere summer season ends in mid- to late August,
the AIM science team will not have to wait long before the Southern
Hemisphere's season starts. This occurs about three months later in mid-
to late November. The Southern season lasts until approximately mid-March
of 2008. Early results from the AIM mission will be reported at a major
international conference focused on PMCs and other high altitude layered
phenomena to be held at the end of August 2007 in Fairbanks, Alaska.
The satellite was launched on April 25, only four weeks before the first
science observations began. During the satellite-commissioning phase and
now in routine observations, all three state-of-the-art instruments have
been working exceptionally well and returning high quality data.
The Cloud Imaging and Particle Size instrument offers a 2-D look at the
clouds, collecting multiple views from different angles. The cameras are
providing panoramic PMC images of the Arctic polar cap daily. The Solar
Occultation For Ice Experiment is measuring new information on cloud
particles: their variability with altitude, the chemicals within the
clouds and the environment in which the clouds form. The Cosmic Dust
Experiment is recording the amount of space dust that enters Earth's
atmosphere to help scientists assess the role this dust plays in PMC
The AIM mission coincides with the two-year, worldwide scientific
community's International Polar Year, and the mission is expected to make
unique contributions to the International Polar Year's objective of
advancing polar research.
AIM is the ninth Small Explorers mission under NASA's Explorer Program and
is managed by the Explorers Program Office at the Goddard Space Flight
Center, Greenbelt, Md. The AIM Project Data Center is located at Hampton