National Science Foundation, Division of Atmospheric and Geospace Sciences, Earth System Models
Multiscale Modeling of Aerosol Indirect Effects on Decadal Timescales
Lynn Russell, Guang Zhang, Richard Somerville, Arthur J. Miller and Dan Cayan
Award: $1,350,000
Duration: 2011-2015
Collaborators: Steven Ghan (Pacific Northwest National Laboratory), Sungsu Park (NCAR)
Project Summary.
Aerosol effects on clouds operate at spatial scales of short-lived cloud updrafts (typically 100 m- 100 km), yet exert a global effect on climate over multiple decades. The multiscale nature of these indirect effects on the planetary energy balance presents particular challenges to climate modeling, which has led to large uncertainties in estimates of indirect effects. The most difficult types of aerosol indirect effects to quantify are those for which the aerosol sources are controlled by complex interactions of ecosystems with climate, such as the aerosol emissions from ocean phytoplankton and from wildfires in forests. The decadal feedbacks of climate onto biological productivity contribute to this uncertainty because of the difficulties in making accurate multidecadal predictions and in collecting detailed observations on comparable time scales.
This proposed project addresses these challenges through a combination of advanced parameterizations, explicit modeling, and observations with a multi-institutional, multidisciplinary team of experts. Advanced parameterizations of aerosol effects on stratocumulus, shallow cumulus and deep cumulus clouds that have been or are being developed under separate funding will be brought together into a common framework for multidecadal simulations with and without coupling with the ocean. These simulations will be compared with available observations and with simulations for selected periods by a multiscale modeling framework (a cloud-resolving model operating as a superparameterization within each grid cell of a global model) that has recently been extended to treat cloud-aerosol interactions. Offline single column simulations with the parameterized and superparameterized cloud-aerosol interactions will be compared with observations for selected field experiments characterizing warm clouds, mixedphase clouds, and cirrus. The coupled and uncoupled simulations with and without interactive aerosols will be examined to determine the influence of aerosol indirect effects on decadal climate variability. This evaluation will be accomplished by relating climate-scale changes in oceanic and atmospheric conditions over the Pacific, including tropical teleconnections and midlatitude downstream effects, to the sensitivities of regional ocean-atmosphere interactions to aerosols along the west coast of North America and consequent atmospheric flows and hydrological conditions over the entire U.S. The evaluation will consider the decadal and interannual variability of clouds, temperature, precipitation, and hydrologic conditions, and the processes affected by aerosols.