A global climatology of ice nucleating particles under cirrus conditions derived from model simulations with MADE3 in EMAC

Kurzfassung

Atmospheric aerosols can act as ice-nucleating particles (INPs) and thereby exert important influences on the formation and the microphysical properties of cirrus clouds and in turn induce distinct climate effects. In laboratory experiments several types of aerosol particles have been identified as efficient INPs under cirrus conditions. However, the knowledge about the global atmospheric distribution of INPs is still limited and consequently the understanding of their climate impacts is highly uncertain. We perform model simulations with a global aerosol-climate model coupled to a two-moment cloud microphysical scheme and a parametrization for aerosol-induced ice formation in cirrus clouds and present a global climatology of INPs in the cirrus regime. This novel INP climatology comprises, in addition to the broadly considered mineral dust and soot INPs, also crystalline ammonium sulfate and glassy organic particles. By coupling the different INP types to the microphysical cirrus cloud scheme, their ice nucleation potential under cirrus conditions is analyzed, considering possible competition mechanisms between different INPs. The simulated INP number concentrations range from about 1 to 100 L-1 and agree well with in-situ observations and other global model studies. Our model results show that glassy organic INP concentrations are mostly low in the cirrus regime, suggesting a small climate impact. On the other hand, crystalline ammonium sulfate often shows large INP concentrations, resulting in a strong potential to influence ice nucleation in cirrus clouds, and should be taken into account, in addition to the effects of mineral dust and soot, in future model applications.