HR: 11:30h
AN: GC52A-08 INVITED    [Abstracts]
TI: The Impact of Cloud Seeding of Marine Stratocumulus on the Ocean Atmosphere System
AU: * Rasch, P J
EM: pjr@ucar.edu
AF: National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307, United States
AU: Chen, C
EM: cchen@ucar.edu
AF: National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307, United States
AU: Latham, J
EM: latham@ucar.edu
AF: National Center for Atmospheric Research, P. O. Box 3000, Boulder, CO 80307, United States
AB: Clouds play a profound role in influencing the energy balance of the Earth system. It is also well known that relatively small variations in cloud properties (drop size, precipitation efficiency, areal extent, cloud lifetime) can produce large changes in the radiative properties of clouds. In 1990 John Latham suggested that a deliberate increase in cloud brightness and longevity (through the introduction of extra Cloud Condensation Nuclei (CCN)) over selected regions of the globe might be used to counteract global warming resulting from increases in greenhouse gases as a geo-engineering strategy. Since that time Latham and colleagues have explored this concept in a variety of studies, exploring the consequences of increases in CCN theoretically, in simple models of particular cloud types, and in an atmospheric general circulation model study employing fixed sea surface temperatures. These latter studies have explored only the change in forcing resulting from a change in cloud albedo, and did not explore the response of the climate system to such a change. They indicated that low (warm) clouds, in regions of lots of sunlight, and susceptible to the introduction of additional CCN might be optimal for this kind of geo-engineering (i.e. the subtropical marine stratocumulus regions). The studies suggested that a significant change in cloud albedo over only a few (approximately 10) percent of the planet would be sufficient to counteract the approximately 4 W/m2 forcing resulting from a doubling of CO2. However, implicit in that result is also the fact that in those relatively small regions where the geoengineering is done, the cloud forcing will be changed very substantially. (As a consequence, it may be preferable to produce smaller albedo changes over a correspondingly larger area). The marine stratocumulus regions are important to the climate system in many ways. They are areas of subsidence above the boundary layer, and play a large role in the Walker and Hadley atmospheric circulations, and they are also areas of oceanic upwelling, and participate in the many aspects of upper ocean dynamical circulations, influencing for example, the source regions of the cold tongue of SSTs that extends into the central pacific, an area important for features like ENSO. In this study we will describe our preliminary findings about the consequences of geoengineering of marine stratus and stratocumulus to the ocean atmosphere system through simulations with slab ocean and fully coupled version of the NCAR Community Climate Sytem Model.
DE: 0300 ATMOSPHERIC COMPOSITION AND STRUCTURE
DE: 0321 Cloud/radiation interaction
DE: 0429 Climate dynamics (1620)
DE: 1626 Global climate models (3337, 4928)
DE: 1807 Climate impacts
SC: Global Environmental Change [GC]
MN: 2007 Fall Meeting