Biological and Environmental Research - Earth and Environmental System Sciences
Earth and Environmental System Modeling

Global simulation of ice-nucleating particles and implications for cloud radiative effects (Invited)

Monday, December 11, 2017 - 08:45
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Ice-nucleating particles (INPs) are known to affect the amount of ice in mixed-phase clouds, thereby influencing many of their properties. We show results of a global model of INP concentrations relevant for mixed-phase clouds based on laboratory and field measurements of ice nucleation by K-feldspar (an ice-active component of desert dust) and marine organic aerosols (from sea spray). The simulated global distribution of INP concentrations based on these two species agrees much better with currently available ambient measurements than when INP concentrations are assumed to depend only on temperature or particle size. Our model indicates that, on a monthly average basis, desert dusts dominate the contribution to the INP population over much of the world, but marine organics become increasingly important over remote oceans and they dominate over the Southern Ocean. We used the model-predicted INP concentrations to simulate ice formation in cyclonic systems over the Southern Ocean using a high-resolution cloud-resolving model. We find that the updated INP model results in mixed-phase clouds with much lower amounts of ice than in the global model, which predicts cloud ice based on a simple temperature threshold. The SW reflectance from the clouds is consequently much greater. These changes suggest that realistic simulations of INP in climate models, coupled with more realistic treatments of mixed-phase cloud microphysics, could improve well-documented radiative biases.

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