Quasi-Lagrangian
measurements of polar stratospheric cloud particle development from
long-duration balloon platforms
National Science
Foundation, $350,251, Nov 2007 - Nov
2010, PI: T. Deshler, CoI: J. Mercer Location:
McMurdo Station,
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.