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Variability in Contrail Ice Nucleation and Its Dependence on Soot Number Emissions
Author(s) -
Bier A.,
Burkhardt U.
Publication year - 2019
Publication title -
journal of geophysical research: atmospheres
Language(s) - English
Resource type - Journals
eISSN - 2169-8996
pISSN - 2169-897X
DOI - 10.1029/2018jd029155
Subject(s) - ice nucleus , soot , atmospheric sciences , ice crystals , nucleation , cirrus , environmental science , climatology , meteorology , physics , chemistry , geology , organic chemistry , thermodynamics , combustion
Abstract Contrail ice nucleation is mainly controlled by aircraft emissions and the atmospheric state. The nucleation rate can have a strong impact on microphysical processes, optical properties, lifetime, and, therefore, on the climate impact of contrail cirrus. We study contrail ice crystal formation offline for specified atmospheric conditions and its spatial variability in a global climate model. Assuming the standard atmosphere, above around 270 hPa (10 km) contrail ice nucleation is mainly controlled by aircraft soot number emissions and below additionally by atmospheric temperature. Parameterizing contrail ice nucleation in a global climate model, we find that in the northern extratropics contrails form frequently far away from their formation threshold. For current soot number emissions and in case of contrail formation, 90% of emitted soot particles form on average ice crystals around the cruise level and more than 70% between cruise altitudes and 300 hPa. The number of nucleated ice crystals in the extratropics decreases nearly at the same rate as soot number emissions. In contrast, in the tropics around cruise altitudes approximately 60% of contrails develop close to their formation threshold so that on average only about 50% of emitted soot particles can form ice crystals. Below, contrail formation occurs rarely and ice nucleation is reduced more strongly. Of the main air traffic areas, contrail ice nucleation is significantly limited by the atmospheric state over eastern Asia and over the southeastern United States. This limitation is enhanced during the summer months.