Session: C12 Poster: M54A A semi-empirical evaluation of cloud activation schemes in climate models Allison McComiskey ; Graham Feingold; Pavlos Kollias; Edward Luke NOAA Earth System Research Laboratory, USA Leading author: [email protected]Boundary layer clouds have a strong influence on climate sensitivity yet present a challenge for climate studies. Climate models struggle to represent the processes that drive shallow cloud development, morphology, interactions with aerosols, and their consequent radiative forcing. Marked uncertainties are associated with cloud drop activation, which influences all of these properties. We employ an empirical approach to representing droplet activation that uses probability distribution functions (PDF) of cloud and aerosol properties over a representative time/area taken from high temporal resolution, point-based measurements. The approach involves building PDFs from radar and radiometer observations that capture the variance across a larger area. Droplet activation is calculated using a cloud parcel model, with model input in the form of random sampling of a joint PDF between the cloud liquid water and vertical velocity, in conjunction with a PDF of observed aerosol properties. This results in knowing the full range of potential activation within the area of interest rather than just the mean. The cloud parcel model is used in various modes to compare the observationally-based activation to various activation schemes used in climate models. Knowing the range of potential activation in a given region or cloud regime from the observations also provides information on the desired uncertainty bounds in the model activation schemes.
Session: C12 Poster: M54A A semi-empirical evaluation of cloud
activation schemes in climate models Allison McComiskey; Graham
Feingold; Pavlos Kollias; Edward Luke NOAA Earth System Research
Laboratory, USA Leading author: [email protected]
Boundary layer clouds have a strong influence on climate
sensitivity yet present a challenge for climate studies. Climate
models struggle to represent the processes that drive shallow cloud
development, morphology, interactions with aerosols, and their
consequent radiative forcing. Marked uncertainties are associated
with cloud drop activation, which influences all of these
properties. We employ an empirical approach to representing droplet
activation that uses probability distribution functions (PDF) of
cloud and aerosol properties over a representative time/area taken
from high temporal resolution, point-based measurements. The
approach involves building PDFs from radar and radiometer
observations that capture the variance across a larger area.
Droplet activation is calculated using a cloud parcel model, with
model input in the form of random sampling of a joint PDF between
the cloud liquid water and vertical velocity, in conjunction with a
PDF of observed aerosol properties. This results in knowing the
full range of potential activation within the area of interest
rather than just the mean. The cloud parcel model is used in
various modes to compare the observationally-based activation to
various activation schemes used in climate models. Knowing the
range of potential activation in a given region or cloud regime
from the observations also provides information on the desired
uncertainty bounds in the model activation schemes.
