Using Multiple Instruments to Better Understand Wind Profiler Observations of the Stratocumulus-Topped Marine Boundary Layer

Stratocumulus (Sc) clouds occur frequently over large portions of the cold waters of the southeastern Pacific Ocean. To better understand and model the radiative effects of these Sc, their thickness needs to be more accurately determined. While the height of Sc cloud bases can be measured effectively by ceilometers, the tops prove to be more difficult. Data from wind profiling radars are often suggested for identifying the top of the marine boundary layer (MBL), which more or less coincides with the top of the Sc deck, but unambiguous interpretation of profiler data in this setting has proved difficult. Multi-platform observations from Pan American Climate Study (PACS) research cruises off the west coast of South America offer a fine opportunity to refine this idea. Here we focus on analyzing and understanding profiler data acquired over the eastern Pacific Ocean during boreal fall 2000 and 2004, with the assistance of both ceilometer and radiosonde data. Monthly mean cloud cover from the International Satellite Cloud Climatology Project (ISCCP) was used to identify days when the ships were likely to have been under Sc. Results from several days show the relative positions of cloud base heights estimated by ceilometers, humidity gradients in radiosonde profiles, and layers of high reflectivity observed by the profilers. The combined platforms also allow us to document the evolution of an internal boundary layer, whose existence shows one more challenge to be overcome if single-platform methods are to be used to determine MBL heights in this region.