Figure 1. Relationship between the fraction of water vapour lost from a precipitating cloud (derived from stable isotope ratios in snow (δ¹⁸O)) and ice nucleating particles (INPs, measured in snow).

As the cloud precipitates, the progressive loss of water vapour (from right to left) is accompanied by a loss of INPs which have been uplifted from the sea and land surfaces (yellow arrows). INPs of biological origin (green half-moons) are activated at more moderate supercooling, hence typically earlier than inorganic INPs (brown hexagons). The values 0.22 and 0.95 correspond to the minimum and maximum fractions of water vapour lost that we observed at Jungfraujoch (drawn by E. Stopelli).