It has been well established that heterogeneous reactions in polar stratospheric clouds (PSCs) are implicated in dramatic losses of ozone over Antarctica in austral spring. Halogen radicals, which originate from volatile anthropogenic compounds that began to be used in the 1930's, catalytically convert ozone to biatomic oxygen in the presence of sunlight and various solid and liquid PSC particles, particularly those bearing nitrogen. What remains unclear from both a theoretical and observational standpoint is exactly how and when key PSC particles, including nitric acid trihydrate (NAT), form. The Office of Polar Programs, Antarctic Science Division, Ocean & Climate Systems Program has made this award to take advantage of super pressure balloon platforms, whose trajectories are along fixed atmospheric density, to sample the PSC particles that occur in the Antarctic polar vortex. Two types of optical particle sensors, one white light and the other laser based, are to be optimized and deployed on long duration balloons (30-90 days) to be launched from McMurdo by the French agency CNES as part of the French-US CONCORDIASI International Polar Year program. The paired sensors will provide basic size fraction and distribution information that along with temperature measurements should provide insight into the conditions under which various PSC particles form. Experience from the VORCORE super pressure balloon program in 2005 indicates that even with duty cycles restricted by power availability, the sensors are highly likely to encounter low enough temperatures to favor NAT, liquid aerosols and ice formation for many 10's of hours during each mission. Such observations from two instrumented missions are expected to lend unprecedented insight into conditions required for in situ PSC particle formation. The results will be compared to satellite and ground (LIDAR) based aerosols measurements as well as model predictions to improve understanding of PSC cloud formation. The proposed project builds on an NSF major research infrastructure grant to the PI to develop and test the cloud particle sensors.
Broader impacts: This project leverages the IPY collaboration with the French who are providing the balloon platforms including their launch, control and data communications system. The proposed project compliments the science to be addressed by the CONCORDIASI IPY program, the primary objective of which is to calibrating satellite born meteorological sensors. A graduate student is to be supported by this project. Three of the nine research group members are female (including the coPI) and so members of an underrepresented group in atmospheric sciences are to be supported.
