11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Thursday, 6 June 2002
Sensitivity of tropical cirrus anvils to convection intensity: Large-eddy simulations with size-resolved, mixed-phase microphysics (Formerly Paper Number 6.5)
Andrew S. Ackerman, NASA/Ames Research Center, Moffett Field, CA; and E. J. Jensen
Recent studies have shown that the response of surface temperature to increasing greenhouse concentrations depends sensitively on the processes controlling tropical cirrus anvil production. As greenhouse gases drive up the sea surface temperature, convection will become more intense. However, it is not clear that increased convective intensity implies larger, longer-lived cirrus anvils. Analysis of satellite observations from the Pacific Warm Pool suggests that precipitation efficiency increases with warming surface temperatures, leading to smaller anvils and significantly reducing the sensitivity of global climate (Lindzen et al., 2001). However, other studies have shown that the opposite sensitivity emerges with slightly different criterion for retrieving upper tropospheric cirrus properties from the satellite measurements.

We are investigating this hypothesis and will present model results from idealized large-eddy simulations with detailed microphysics. Our model resolves the size distributions of dry aerosols, liquid droplets, ice crystals, and mixed-phase hydrometers, and treats the microphysical processes of droplet activation, freezing, melting, homogeneous freezing of sulfate aerosols, and heterogeneous ice nucleation. For our simulations we will investigate the sensitivity to convective intensity of the moisture mass flux into anvils, as well as the variations in anvil size and lifetime with convective intensity.

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