MASRADIOP

MArine Stratus Radiation Aerosol and Drizzle (MASRAD) IOP

14 March 2005 - 14 September 2005

Lead Scientist: Mark Miller

Observatory: AMF , PYE

The ARM Mobile Facility (AMF) was deployed to Point Reyes National Seashore on the California coast to study the microphysical and radiative characteristics of marine stratus, one of the most prevalent clouds on Earth. Marine stratus is an important yet undersampled component of the Earth’s climate system. These clouds are known to be susceptible to infusions of human-caused aerosols that likely alter the in-cloud microphysical processes and are known to have at least two stable modes: one with relatively large cloud droplets and relatively large drizzle rates, and another with relatively smaller cloud droplets and little or no drizzle. Cloud condensation nuclei (CCN) apparently play a critical role in determining which stable mode is observed. Marine stratus clouds also exhibit a strong diurnal cycle due to a pronounced cloud and radiation feedback involving changes in the net radiative flux at the cloud top. Researchers had two main scientific objectives: 1) to investigate the general relationship between cloud mesoscale structure, aerosols, cloud microphysics, drizzle, and radiation in marine stratus clouds; and 2) the specific effects of aerosols on the discrepancy between the measured and modeled amount of solar radiation absorbed by these clouds. These scientific objectives were investigated by combining detailed cloud, drizzle, and radiation measurements from the AMF 94-GHz radar and other sensors with detailed aircraft profiles, which included comprehensive aerosol measurements. The effects of aerosols on the amount of solar radiation absorbed by marine stratus were quantified using similar methods supplemented by state-of-the-art in-cloud radiation measurements made from aircraft. These combined measurements improved on previous studies addressing the discrepancy between models and observations of the solar absorption of clouds by direct and accurate observation of the ambient aerosols, surface albedo, and downwelling solar flux. In particular, highly accurate solar flux measurements were obtained from a state-of-the-art, stabilized platform for making radiometric measurements from an aircraft. The research proposal leveraged experimental activities conducted in the Point Reyes area during the summer of 2005 in conjunction with research supported by the Office of Naval Research (ONR), the Naval Research Laboratory, and the DOE Aerosol Science Program. The ONR experiments included the use of a scanning (military, phased array) X-band (3.2-centimeter wavelength), scanning Doppler radar to study the mesoscale organization of drizzle patches embedded in marine stratocumulus in the region. There were opportunities for coincident aerosol and radiation data to be collected in the vicinity of the AMF site with the CIRPAS Twin Otter and Pacific Northwest National Laboratory G-1 research aircraft.