Sunday, 22 January 2012
Understanding Wind Profiler Observations of Stratocumulus-Topped Marine Boundary Layer
Hall E (New Orleans Convention Center )
Clouds directly affect Earth's energy budget by changing the planet's albedo and the balance of incoming and outgoing radiation. Of particular interest are marine stratocumulus (Sc), which typically play the important role of cooling the planet. To fully understand Sc and their effects, and to improve modeling, their thickness needs to be more precisely determined. While cloud bottoms can be measured effectively by ceilometers, the tops are more difficult. Wind profiler data are often suggested as an aid in identifying the top of the marine boundary layer (MBL), which coincides with the top of Sc, but the interpretation of the data is often difficult. This project focuses on analyzing and understanding profiler data acquired over the eastern Pacific Ocean, with the assistance of both ceilometer and radiosonde data. Data were acquired during a Pan American Climate Study (PACS) research cruise in fall 2004. The ship sailed through the eastern Pacific Ocean just off the west coast of South America. Monthly averages from the International Satellite Cloud Climatology Project (ISCCP) were used to identify days when the ship was likely under Sc. On those days, the wind profiler data showed a high reflectivity layer. The ceilometer measured cloud base heights that never surpassed the reflectivity layer's height. The sonde measurements of relative humidity decreased sharply across the layer, indicating the presence of the inversion that caps the MBL. This project determined that the height of the MBL top was at the height of the inversion shown by the radiosonde.