Are Atmospheric Vertical Velocities a Key to Unlocking Climate Forcing and Sensitivity?

Abstract:

The roles of moist processes both as feedbacks to climate forcing and,
in the case of their interactions with aerosols, as sources of climate forcing
remain stubbornly uncertain. This presentation will argue that a possible
breakthrough in reducing this uncertainty may be found through closer at-
tention to vertical velocities in climate models. Vertical velocities are a pri-
mary driver of nucleation of cloud droplets and ice crystals in clouds and
thereby climate forcing by cloud-aerosol interactions. They may also be im-
portant, observably veriable constraints on convective processes important
for cloud feedbacks, as they correlate with convective mixing and vertical
heating proles.

Limited attention has been directed to the realism of the vertical-velocity
spectrum in climate models. To the extent vertical velocities are critical
in climate forcing and as a constraint on climate feedbacks, this opens new
opportunities to reduce uncertainties in forcing and feedbacks. Vertical ve-
locities on all scales are likely to be important. These scales are both resolved
and sub-grid in climate models. Recenteld campaigns have provided new
observations of vertical velocities at cloud scales, and parameterizations for
moist processes in models are beginning to include vertical velocities. Ex-
ploiting information on vertical velocities in climate models, and foreseeable
advances in parameterization and model resolution with attention to vertical
velocities, oer the prospect of reducing uncertainty associated with moist
processes.