Both climate forcing and climate sensitivity persist as stubborn uncertainties limiting the extent to which climate models can provide actionable scientific scenarios for climate change. A key, explicit control on cloud-aerosol interactions, the largest uncertainty in climate forcing, is the vertical velocity of cloud-scale updrafts. Model-based studies of climate sensitivity indicate that convective entrainment, which is closely related to updraft speeds, is an important control on climate sensitivity. Updraft vertical velocities also control many physical processes essential to numerical weather prediction.

    Vertical velocities and their role in atmospheric physical processes have been given very limited attention in models for climate and numerical weather prediction. The relevant physical scales range down to tens of meters and are thus frequently sub-grid and require parameterization. Many state-of-science convection parameterizations provide mass fluxes without specifying vertical velocities, and parameterizations which do provide vertical velocities have been subject to limited evaluation against what have until recently been scant observations. Observed velocity structure functions suggest that accurate explicitly simulated vertical velocities are functions of model resolution, a dependence not accounted for when physically based representations of cloud processes are included in current models.

    The emergence of new observations of convective vertical velocities offers a potentially promising path toward developing process-level cloud models and parameterizations for climate and numerical weather prediction. Taking account of scale-dependence of resolved vertical velocities offers a path to matching cloud-scale physical processes and their driving dynamics more realistically, with a prospect of reduced uncertainty in both climate forcing and sensitivity.

主讲人简介：

    Dr. Donner is a senior scientist at GFDL and joint professor at Princeton University. He got his Ph.D from University of Chicago with professor Kuo Hsiao-lan (郭晓岚) in 1983. He was an assitant professor at University of Chicago after worked as a postdoc and scientist at NCAR. He has been at GFDL since 1991 and the chair for GFDL AM3 model development. He is now the chair of Community Earth System Model Advisory Board and has been the editor for J. of Climate and advisory board for many organizations and journals. Dr. Donner developed a cumulus parameterization scheme, which has been used in GFDL AM3 model. His research area is cloud and convective processes in the atmospheric general circulation.