Cloud particle size distributions (PSDs) are crucial in determining the clouds physical and optical properties and hence their radiative feedback to the climate. Here we present unprecedented occurrence patterns of ice crystals in cirrus clouds derived from 270 h of cloud measurements (≈ 975 000 PSDs).

In particular, cirrus PSDs for cold to warm cirrus temperatures and microphysically thin to thick cirrus clouds are provided in a novel presentation as heat maps. The observations are accompanied by simulations of ice crystal growth in in-situ-origin cirrus.

Larger crystals most likely originate from clouds that formed at lower altitudes and rose into the cold cirrus layers, where the cloud particles glaciate. The combined evaluation of observations and simulations allows the attribution of processes shaping the PSDs.

Important results are that, as temperature and cirrus thickness decrease, the prevailing ice particle population evolves from larger and more abundant crystals characteristic of liquid-origin cirrus to few, small crystals typical of in situ-origin cirrus. This shift in cirrus origin is associated with substantially different climate feedbacks.

Lieu
École normale supérieure – PSL
24 rue Lhomond – aile Erasme
salle Claude Froidevaux – E314