Ice water content‐extinction relationships and effective diameter for TTL cirrus derived from in situ measurements during ATTREX 2014

The NASA Airborne Tropical Tropopause Experiment (ATTREX) deployment in January–March 2014 yielded more than 34 hours of cirrus cloud sampling in the tropical tropopause layer (TTL) over the western Pacific. Cirrus were encountered throughout the TTL, at temperatures between 185 and 207 K, with ice water content (IWC) ranging from > 10 mg m-3 to below the instrumental detection limit of 1 µg m-3. Geometric optical extinction (σ) values determined from cloud particle probe measurements ranged from 10-3 m-1 to   192 K was 40 – 50 µm and exhibited a weak temperature dependence, while colder than 192 K, Deff decreased more strongly with decreasing T. From the ATTREX data, a new parameterization of the IWC-σ relationship for TTL cirrus is derived that will improve the estimation of IWC from lidar and optical probe observations of these clouds.