Quasi-Lagrangian
measurements of polar stratospheric cloud particle
development from
long-duration balloon platforms
In
the past twenty years there has been a rapid decline in
Antarctic
stratospheric
ozone in austral spring. This decline is due to halogens
released into
the
atmosphere since the 1930s. In the stratosphere these halogen
molecules
are
converted to less stable molecules which can then interact
with
particles,
converting inactive to active chlorine. When this occurs it
can lead to
rapid,
chlorine induced, catalytic
conversion of
ozone to
diatomic oxygen in the presence of sunlight. This ozone loss
is
confined to the
polar regions, particularly the
austral
polar region,
because of its dependence on the presence of particles, and
thus polar
stratospheric clouds. A further investigation of the formation
processes in these
clouds is the purpose of this International Polar Year (IPY)
proposal.
We
propose to take advantage of two recent developments which
make it
possible for
the first time to make quasi-Lagrangian in situ measurements
of aerosol
particle size and number concentration from a long duration
balloon.
The intellectual
merit of this work lies in using this opportunity to
capture the
processes
of particle growth during the formation and dissolution of
polar
stratospheric clouds
(PSCs),
as the
instruments pass into and out of temperature regimes favorable
for PSC
development. The particle measurements along with temperature
measurements will
allow observations of the threshold temperatures for PSC
particle
condensation
forming liquid cloud particles, including some estimates of
their
growth rate,
and possibly observations of the nucleation rate/threshold for
the
formation of
nitric acid trihydrate (NAT) particles. The question of how
NAT
nucleates
within a PSC is one of the major unanswered question
concerning PSC particle development. Observations of non-PSC
aerosol as
PSC
temperatures are approached will add to our understanding of
the
characteristics of the seed bed for PSC growth. These
observations also
have
the chance to document the existence of large PSC particles in
the
Antarctic.
The
two developments which
make this possible are: 1) The
development
by the
French Centre National d’Etudes Spatiales (CNES) of super
pressure
balloons
which can survive polar stratospheric temperatures. In
September/October 2005
CNES demonstrated its ability to deploy these isopycnic
balloons into
the
Antarctic winter polar vortex from McMurdo Station. These
balloons,
which float
on a constant air density surface,
stayed aloft for 30-90 days. We
contributed to this campaign in 2005 and maintain scientific
collaboration with
Drs. Francois Vial and Dr. Albert Hertzog, Laboratoire
Meterologique
Dynamique,
France, and technical collaboration with Mr. Philippe
Cocquerrez, CNES.
Based
on this collaboration we have been invited by these
individuals to join
their Concordiasi campaign
(a French IPY project)
planned for
September
2008 from McMurdo Station,
The broader
impacts
of this work have several aspects. This research will explore
new
possibilities
for long-duration mid-stratospheric based platforms for in
situ aerosol
measurements. This capability may have broader implications
than the
specific
measurements planned for this project. For example tropical,
near
tropopause,
measurements of subvisible cirrus are of high interest for
improving
our
understanding of the impact of clouds on climate. In addition
new
satellite
sensors (on Calipso and Parasol) provide fruitful ground for
measurement
comparisons in the polar regions.
This
research
contributes to the careers of a staff scientist, engineer,
technician,
and
graduate students. Three of the nine members of this group are
women
(including
the co-PI here), thus increasing
the
contribution of
underrepresented groups in science.
Progress on this project:
First year
annual
progress report Acknowledgment
of
receipt of progress report
Calibrations
and
laboratory tests completed on the six instruments (J4p -
J9p) purchased
and developed for this project.