VOCALS: Comprehensive Studies of Marine Stratocumulus during VOCALS-REx Using Airborne Radar, Lidar, and In Situ Measurements

University Of Wyoming, Laramie WY

Investigators

Abstract

It is now recognized that drizzle is a common feature of marine stratocumulus clouds and that it has an important impact on the heat, water, and aerosol budgets of cloud decks. Additionally, analyses of mesoscale organization in marine stratocumulus clouds (typically on a scale of 5 - 100 km) show that drizzle is the key process linking mesoscale organization and cloud microphysical processes. The formation of pockets of open cells (POCs), which is believed to result from drizzle-aerosol-cloud interactions, results in large changes in cloud-fraction and albedo - properties of cloud decks that are significant for the climate. While the formation of POCs is the most dramatic example of these linkages, it is only one of many manifestations of drizzle-aerosol-cloud interactions that determine the characteristics of the stratocumulus layer. As such, there is a pressing need for observational studies that provide quantitative estimates of drizzle rates and of processes directly linked to drizzle (such as the removal of aerosol particles) and for a comprehensive depiction of the kinematic, thermodynamic, and cloud-microphysical structure within different types of mesoscale organization; these can be used to investigate drizzle-cloud structure linkages and for comparison with structures obtained from numerical simulations. This project will contribute to the quantitative and qualitative needs by deploying a suite of instruments on the NSF C-130 aircraft during VOCALS-REx (VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment). Measurements that will include: vertical cross-sections of radar reflectivity and Doppler velocity, measurements of cloud-base height, cloud condensation nuclei (CCN), aerosol, and hydrometeor size spectra. Reflectivity cross-sections and vertical-plane velocity fields from the radar will be used to identify and characterize mesoscale structures within the stratocumulus-topped boundary layer and, through the use of a conditional sampling approach, to develop a composite depiction of mesoscale structures. Radar cross-sections will also provide a context for other measurements made onboard the NSF C-130. Expected outcomes include: quantitative estimates, which will be incorporated into integrated VOCLALS-REx datasets, of: precipitation rate (cloud-base and sea surface), cloud-base and cloud-top heights, sub-cloud aerosol and CCN spectra, and the rate of CCN removal due to drizzle; an assessment of probable mechanisms underlying the transition from unbroken to broken marine stratocumulus will be made using the composite depictions of the mesoscale structures. Two broader impacts are expected: First, in collaboration with other VOCALS investigators, integrated datasets from VOCALS-REx will be compiled and made available to the atmospheric science community. In conjunction with other VOCALS-REx investigators, parameterizations of cloud microphysical processes in terms of cloud macrophysical characteristics will be developed. Second, expertise in the synergistic use of radar, lidar and in situ observations will be developed through graduate student training.