AIM is the first satellite mission dedicated to the study
of noctilucent or “night-shining” clouds (NLCs)
also called Polar Mesospheric clouds (PMCs). It has provided
the first global-scale view of the clouds over the entire
2007 Northern Hemisphere season with an unprecedented resolution
of 5 km by 5 km and is nearing completion of observations
in the Southern Hemisphere season. Despite a significant
increase in PMC research in recent years, relatively little
is known about the basic physics of these clouds at ”the
edge of space” and why they are changing. They have
increased in brightness over time, are being seen more often
and appear to be occurring at lower latitudes than ever
before. The overall goal of the baseline mission is to determine
why PMCs form and vary. Since the launch of AIM on April
25, 2007, significant progress has been made in achieving
this goal and that progress continues at a rapid rate. The
AIM data is of very high quality and has changed our view
of PMCs and their environment after only one northern hemisphere
(NH) season of observations. The startling similarity between
the PMC structure observed by CIPS and that seen in tropospheric
clouds suggests that the mesosphere may share some of the
same dynamical processes responsible for weather near Earth’s
surface. If this similarity holds up in further analysis,
it introduces an entirely different view of potential mechanisms
responsible for PMC formation and variability.
The AIM spacecraft, instruments, and all subsystems are
healthy and fully functional. An intermittent issue with
the uplink has been mitigated by adding full autonomy to
the spacecraft and instruments and enabling 24 days worth
of command loads. AIM is fully prepared to deliver the exciting
new science enabled by an extended mission.
We propose here to extend the mission through 2012. This
3-year extension will allow AIM to address new science that
requires a longer period of observations and opens the way
for deeper probing of the mysteries surrounding the causes
of why these clouds form and vary.
The extended mission will provide data during the rising
phase of the solar cycle to address solar effects on PMC
formation under varying solar conditions. The longer data
record will allow interannual variations in atmospheric
properties to be characterized and correlated with PMC changes.
The question of teleconnection focuses on the provocative
new suggestion that the summertime phenomenon of PMCs is
strongly driven by the winter hemisphere. These objectives
directly address two of four Heliophysics focus areas for
the objective “Understand the Nature of Our Home in
Space” including: 1) Determine changes in the Earth’s
magnetosphere, ionosphere, and upper atmosphere to enable
specification, prediction, and mitigation of their effects
and 2) Understand the role of the Sun as an energy source
to Earth’s atmosphere and in particular, the role
of solar variability in driving change. The mission also
directly addresses two Earth Science focus areas including
atmospheric composition and climate variability and change.
Major Findings
from the First NH Season
AIM has provided the most detailed
picture of NH clouds ever collected:
• The clouds appear every day, are widespread
and are highly variable on hourly to daily time scales.
• PMC brightness varies over horizontal scales
of a few kilometers, and because of the AIM high horizontal
resolution, we now know that over small regions the
clouds are ten times brighter than measured by previous
space-based instruments.
• A previously suspected, but never before seen,
population of very small ice particles was measured
that is believed to be responsible for strong radar
echoes from the summertime mesosphere.
• Mesospheric ice occurs in one continuous layer
extending from below the main peak at 83 km up to around
90 km.
• Mesospheric cloud structures, resolved for the
first time by the CIPS imager, exhibit complex features
present in normal tropospheric clouds.
Extended Mission
Science Objectives
• Are there temporal variations
in PMCs that can be explained by changes in solar irradiance
and particle input?
• What changes in mesospheric properties are responsible
for north/south differences in PMC features?
• What atmospheric properties are responsible
for interannual variability in PMCs?
• What is the mechanism of teleconnection between
winter temperatures and summer hemisphere PMC’s?
• An optimal funding study of gravity waves is
proposed: What is the global occurrence rate of gravity
waves outside the PMC domain?
