Ackerman et al. 2008, in press

Ackerman, A.S., M.C. van Zanten, B. Stevens, V. Savic-Jovcic, C.S. Bretherton, A. Chlond, J.-G. Gloaz, H. Jiang, M. Khairoutdinov, S.K. Krueger, D.C. Lewellen, A. Lock, C.-H. Moeng, K. Nakamura, M.D. Petters, J.R. Snider, S. Weinbrecht, and M. Zulauf, 2008: Large-eddy simulations of a drizzling, stratocumulus-topped marine boundary layer. M. Weather Rev., in press, doi:10.1175/2008MWR2582.1.

Cloud-water sedimentation and drizzle in a stratocumulus-topped boundary layer are the focus of an intercomparison of large-eddy simulations. The context is an idealized case study of nocturnal stratocumulus under a dry inversion, with embedded pockets of heavily drizzling open cellular convection. Results from eleven groups are used. Two models resolve the size distributions of cloud particles, and the others parameterize cloud-water sedimentation and drizzle. For the ensemble of simulations with drizzle and cloud-water sedimentation, the mean liquid water path (LWP) is remarkably steady and consistent with the measurements, the mean entrainment rate is at the low end of the measured range, and the ensemble-average maximum vertical wind variance is roughly half that measured. On average, precipitation at the surface and at cloud base is smaller, and the rate of precipitation evaporation greater, than measured. The vertical gradient of moisture correlates well with LWP but not with precipitation. LWP is well-correlated with the ratio of radiative cooling to the sum of entrainment warming plus latent heating associated with precipitation, a correlation largely determined by model dynamics. LWP is also influenced by microphysics, decreasing as the propensity for drizzle is increased. Including cloud-water sedimentation in the simulations always decreases entrainment substantially and increases LWP. In contrast, LWP nearly always decreases in response to including drizzle. In all but a few cases cloud-water sedimentation dominates the LWP response to drizzle. The omission of cloud-water sedimentation in simulations is strongly discouraged, even for clouds not precipitating below cloud base.

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Ackerman, A.S., van Zanten, M.C., Stevens, B., Savic-Jovcic, V., Bretherton, C.S., Chlond, A., Gloaz, J.-G., Jiang, H., Khairoutdinov, M., Krueger, S.K., Lewellen, D.C., Lock, A., Moeng, C.-H., Nakamura, K., Petters, M.D., Snider, J.R., Weinbrecht, S., and Zulauf, M.: Large-eddy simulations of a drizzling, stratocumulus-topped marine boundary layer, M. Weather Rev., in press, doi:10.1175/2008MWR2582.1, 2008.

Ackerman, A.S., M.C. van Zanten, B. Stevens, V. Savic-Jovcic, C.S. Bretherton, A. Chlond, J.-G. Gloaz, H. Jiang, M. Khairoutdinov, S.K. Krueger, D.C. Lewellen, A. Lock, C.-H. Moeng, K. Nakamura, M.D. Petters, J.R. Snider, S. Weinbrecht, and M. Zulauf (2008), Large-eddy simulations of a drizzling, stratocumulus-topped marine boundary layer, M. Weather Rev., in press, doi:10.1175/2008MWR2582.1.

Ackerman, A.S., M.C. van Zanten, B. Stevens, V. Savic-Jovcic, C.S. Bretherton, A. Chlond, J.-G. Gloaz, H. Jiang, M. Khairoutdinov, S.K. Krueger, D.C. Lewellen, A. Lock, C.-H. Moeng, K. Nakamura, M.D. Petters, J.R. Snider, S. Weinbrecht, and M. Zulauf, 2008: Large-eddy simulations of a drizzling, stratocumulus-topped marine boundary layer. M. Weather Rev., in press, doi:10.1175/2008MWR2582.1.

Ackerman, A.S., et al. 2008, M. Weather Rev., in press, doi:10.1175/2008MWR2582.1.

Ackerman AS, van Zanten MC, Stevens B, Savic-Jovcic V, Bretherton CS, Chlond A, Gloaz J-G, Jiang H, Khairoutdinov M, Krueger SK, Lewellen DC, Lock A, Moeng C-H, Nakamura K, Petters MD, Snider JR, Weinbrecht S, Zulauf M. Large-eddy simulations of a drizzling, stratocumulus-topped marine boundary layer, M Weather Rev 2008, in press. doi:10.1175/2008MWR2582.1.

A.S. Ackerman, M.C. van Zanten, B. Stevens, V. Savic-Jovcic, C.S. Bretherton, A. Chlond, J.-G. Gloaz, H. Jiang, M. Khairoutdinov, S.K. Krueger, D.C. Lewellen, A. Lock, C.-H. Moeng, K. Nakamura, M.D. Petters, J.R. Snider, S. Weinbrecht, M. Zulauf, M. Weather Rev., doi:10.1175/2008MWR2582.1, in press.