Collaborative Research: IPY: GLIMPSE-Airborne Studies of polar stratospheric cloud particle formation mechanisms near the Antarctic Peninsula.

National Science Foundation, $289,310, January 2008 – January 2011, PI: T. Deshler Location: Punta Arenas, Chile Submitted: 9 March 2007.

The Global Climate Change and Antarctic Peninsula Atmospheric Forcing (GLIMPSE) program is a component of the Antarctic Climate and Atmospheric Circulation study that has been endorsed by the International Project Office for the International Polar Year (IPY; see full proposal #180 at http://www.ipy.org). This proposal is submitted in response to the IPY 2007 Program Solicitation NSF 07-536 and the research will address issues in the emphasis area of “Understanding Environmental Change in Polar Regions”. The goal of GLIMPSE is to examine in detail the tropospheric and stratospheric response to external forcing in the Weddell Sea sector. The central geographical feature of interest is the Antarctic Peninsula, a narrow mountainous band no wider than 30 km in certain places with mountainous peaks reaching in excess of 2000 m. The Antarctic Peninsula serves as a formidable barrier to stable air flow from both the east and west and is an effective climatic divide between the Weddell Sea to the east and the Bellingshausen Sea to the west. The lower atmosphere adjacent to the Antarctic Peninsula is one of the most rapidly warming places on Earth and is thought by many to provide early regional evidence of “global warming”. Surface temperatures along the west side of the Antarctic Peninsula have increased by nearly 3°C over the past 50 years, nearly 10 times the global average. The stratosphere downwind of the Antarctic Peninsula is known as a source region for stratospheric clouds. In these clouds solid and liquid particles form which then provide surfaces for the conversion of inactive to active chlorine and eventually polar ozone loss.

It is proposed within the IPY-GLIMPSE collaboration to deploy the High Performance Instrumented Airborne Platform for Environmental Research (HIAPER) from Punta Arenas, Chile, during August 2009 to conduct airborne investigations of the interaction of mean tropospheric circulations with the Antarctic Peninsula under conditions representative of the positive and negative polarity of the Southern Hemisphere Annular Mode (SAM), and to couple these investigations with polar stratospheric cloud measurements. Coincident with the regional warming has been a trend toward a positive polarity in the SAM, which in turn has been related to recent trends in stratospheric circulations resulting from photochemistry of ozone depletion. The goal and intellectual merit of this proposal within the IPY-GLIMPSE collaboration is to make measurements of the formation of solid polar stratospheric cloud particles in a region of the Antarctic known for such clouds, yet without previous detailed measurements. While the formation of liquid stratospheric cloud particles is well understood, there are still significant questions concerning the formation of solid nitric acid hydrates in these clouds. This is important because these particles are stable at the warmest temperatures which will sustain these clouds, and can thus provide surfaces for heterogeneous chemistry when no other surfaces are available, and can grow large enough to denitrify the stratosphere, further prolonging chemical ozone loss. While the coldest stratospheric air is often displaced over the Weddell Sea and there are satellite observations of stratospheric clouds there, detailed measurements of the clouds in this area have not been completed. Measurements of the formation region of the solid hydrates along with temperature and estimates of gas phase mixing ratios will go a long way to constraining the conditions necessary to nucleate these hydrates.

GLIMPSE will take place during the International Polar Year (IPY) and is responsive to IPY science goals of understanding change and demonstrating the global significance of the polar regions. HIAPER will bring state-of-the-art airborne research tools to bear on one of the most remote, and important, yet poorly studied regions of our planet, thus promoting NSF’s active participation in IPY. These broader impacts are supplemented with new possibilities for tropospheric/stratospheric measurements over the Weddell Sea, with the potential to improve our understanding of the atmospheric conditions under which solid stratospheric cloud particles form, thus improving our understanding of polar ozone loss, a problem with global implications. In addition new satellite sensors (on CALIPSO and PARASOL) provide fruitful ground for measurement comparisons in the polar regions. A vigorous education program to graduate students, early career researchers, and the general public, a characteristic of IPY as a whole and the GLIMPSE proposals in particular, will be supported here. This research contributes to the careers of a staff scientist and graduate students, some of whom are from underrepresented groups within science.