Diurnal Variations in Cloud Properties over the Eastern Pacific From GOES-8 During EPIC 2001

Patrick Minnis, Louis Nguyen, Atmospheric Sciences, NASA Langley Research Center, Hampton, VA 23681 USA

[p.minnis@nasa.gov]

J. Kirk Ayers, AS&M, Inc., Hampton, VA 23681 USA

Project Web Site: http://www-pm.larc.nasa.gov/pacs-epic/pacs-epic.html

Abstract

U.S. CLIVAR PanAmerican Workshop, Boulder, CO, September 15-18, 2003

Satellite measurements of cloud properties and the radiation budget are essential for understanding meso- and large-scale processes that drive the circulation over the eastern Pacific. The measurements taken by the R/V Ron Brown EPIC 2001 provide highly detailed characterizations of the state of ocean and atmosphere at the particular time and location of the ship. Because the marine boundary layer is subject to substantial variations at the diurnal scale, it is important to monitor the cloud field continuously at a given spot or in a Lagrangian sense to better model the interactions between the sea and the atmosphere. The Geostationary Operational Environmental Satellite (GOES) imager can be used to provide a less detailed, but temporally and spatially comprehensive characterization of the cloud fields over the entire domain. The data can be used to perform both static and Lagrangian studies of the interactions between the clouds, the radiation budget, the atmospheric state, and the surface, especially as related to the diurnal cycle.

This paper describes the cloud and radiation data derived from GOES-8 during the EPIC 2001 period. Hourly 4-km GOES-8 imager data were analyzed to derive cloud coverage, height, optical depth, effective droplet radius, liquid water path, and temperature, as well as the top-of-the-atmosphere radiation budget. The domain covers 15°N to 20°S and 70°W to 105°W, a subset of the larger satellite domain used for the PACS cloud climatology. It includes the path of the R/V Ron Brown  during the experiment. The pixel-level results are averaged over a fixed grid and used to determine the mean diurnal variations of the cloud fields over the tropical eastern Pacific and the adjacent portions of Central and South America to help understand the connection between the continental convection and the marine boundary layer. The spatial variations of the cloud microphysical properties are also analyzed to provide preliminary estimates of the influence of continental aerosols and drizzle on the cloud properties. The results of these analyses should provide new insight into the spatial and temporal variability of marine boundary layer clouds and their role in the circulations over the Eastern Pacific.