An Integrated Cavity Output Spectrometer for In-situ Water Isotopologue Measurements of HDO and H2O in the Asian Summer Monsoon

Abstract:

The Asian monsoon is one of the main pathways by which water vapor enters the UT/LS. However, its contributions to the total stratospheric water budget are not well constrained. The isotopic composition of water vapor is a useful tracer for the convective and microphysical history of air parcels. In-situ, isotopic measurements of air in the UT/LS during the monsoon could be used to constrain its contribution to stratospheric water, to provide a check on satellite measurements, and to help distinguish between in-situ and convective tropical cirrus, which are important to Earth’s radiation budget. We show how isotopologue measurements can act as a tracer for convective detrainment of water vapor, and discuss the design of a cavity-enhanced water isotopologue spectrometer that will fly aboard the M55 Geophysica as part of the 2016 Asian Summer Monsoon StratoClim campaign. The spectrometer will sample air in the 14-21 km range, and must make 2 Hz measurements of precision 20 per mil in δD to distinguish air parcels of different origin. These measurements will be analyzed in concert with those taken by other StratoClim instruments to better understand the origins of moisture in the UT/LS and the formation of tropical cold cirrus.