High-Sensitivity TDL Measurements of Water Isotopologues for UTLS studies

Water vapor isotopic composition tracks the convective and microphysical history of air parcels, and is of potential use for diagnosing the origin and evolution of UTLS cirrus. We discuss design considerations and science applications for in-situ measurements of water isotopologues both in the UTLS itself and in cloud chambers that replicate UTLS conditions. We describe a new 2.67 micrometer tunable diode laser spectrometer for measurements of water and its isotopologues down to 195 K at the AIDA Cloud and Aerosol Chamber and extensions to in situ measurements. Measurement sensitivity of the HDO:H2O ratio during cloud formation at AIDA is within 1% (10 per mil). In situ measurements of similar quality can aid in understanding UTLS cirrus formation, including identification of "secondary" cirrus related to past convective detrainment.