CPZRD

Marine ARM GPCI Investigations of Clouds (MAGIC): Cloud Properties from Zenith Radiance Data

1 October 2012 - 30 September 2013

Lead Scientist: J.-Y. Christine Chiu

Observatory: AMF, MAG

Cloud droplet size and optical depth are the most fundamental cloud properties for understanding cloud formation, dissipation and interactions with aerosol and drizzle. They are also a crucial determinant of the Earth’s radiative and water energy balance. However, these properties are poorly predicted in climate models. As a result, the response of clouds to climate change is one of the major sources of uncertainty in climate prediction. To understand the feedback processes of marine boundary layer clouds, the AMF2 MAGIC field campaign aimed to observe the transition from the stratocumulus to shallow trade-wind cumulus. These clouds pose great challenges for remote sensing techniques because of their highly inhomogeneous and fast evolving nature. We aimed to provide observations of cloud optical depth and effective droplet size at high temporal resolution using the ARM sunphotometer, which has a proper narrow field-of-view for observing broken clouds and the necessary narrow wavelength bands. The cloud properties were retrieved from a physical-based method and complemented retrievals from flux, microwave and active sensors. The proposed campaign had three goals. First, estimate liquid water path by the retrievals. By combining the retrieved liquid water path with that from microwave measurements, we can better understand the vertical distribution of liquid water content, and investigate its effect on cloud dynamics. Second, cloud droplet size retrievals are unique to this method and were used to investigate the link between cloud droplet size and precipitation efficiency. Third, sunphotometer measurements were compared to those from the new ARM shortwave spectrometer (SAS-Ze) to explore new uses of the spectrometer. Finally, sunphotometers have demonstrated robust performance in worldwide AERONET sites under all kinds of weather conditions and were easy to deploy. Therefore, the proposed sunphotometer deployment was a pathfinder not just for seagoing deployments, but also for many future deployments.