First estimates of Tropical Tropopause Cirrus lifetimes using balloon-borne lidar observations

Tropical tropopause layer (TTL) cirrus clouds play a key role in the Earth climate system, yet the relative role of the various processes shaping them remains poorly known. Characterizing the temporal evolution of cloudy structures from observations is essential to address this issue, but represents a challenge. Indeed, space- and air-borne platform are not well-suited for this task: moving much faster than the air, they only provide instantaneous snapshots. In boreal winter 2021-2022, two balloon-borne lidars flew over the Equatorial Pacific Ocean, slowly drifting above the clouds. We use those unique observations of truncated (nighttime only) lifetime distribution to quantify the underlying continuous distribution of cloud lifetime above this homogeneous region. While most clouds are short-lived (mean lifetime estimated at about 6 h, a median value of 1 h), the temporal cloud cover is still dominated by the few long-lived ones (24 h or more). These results are compared to cirrus lifetimes in ERA5 reanalysis, showing a fair agreement between the reanalysis and the observations, and demonstrating the value of our approach to evaluate cirrus representation in global models.