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Impact of small ice crystal assumptions on ice sedimentation rates in cirrus clouds and GCM simulations
Author(s) -
Mitchell David L.,
Rasch Philip,
Ivanova Dorothea,
McFarquhar Greg,
Nousiainen Timo
Publication year - 2008
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2008gl033552
Subject(s) - cirrus , ice crystals , climatology , environmental science , troposphere , atmospheric sciences , gcm transcription factors , forcing (mathematics) , climate sensitivity , climate model , radiative forcing , ice cloud , climate change , cloud computing , meteorology , geology , general circulation model , geography , oceanography , computer science , operating system
In the prediction of climate change, the greatest uncertainty lies in the representation of clouds. Ice clouds are particularly challenging, and to date there is no accepted method for measuring the smaller ice crystals (D < 60 μ m). This study examines the sensitivity of a global climate model to different assumptions regarding the number concentrations of small ice crystals when they are allowed to affect ice sedimentation rates. When their concentrations are relatively high, the GCM predicts a 12% increase in cloud ice amount and a 5.5% increase in cirrus cloud coverage globally. This produces a net cloud forcing of −5 W m −2 in the tropics and warms the upper tropical troposphere over 3°C. Ice crystal concentration differences assumed were modest in comparison to corresponding measurement uncertainties, revealing a potentially large source of uncertainty in the prediction of global climate.

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