An Analysis and Model Evaluation of the Marine Boundary Layer Height in the Eastern Pacific

The atmospheric boundary layer (ABL) couples ocean surface processes with clouds and convection over the eastern Pacific. The determination of the boundary layer height is therefore crucial in the parameterization of the ABL in numerical weather prediction and climate models. Here, a method to determine the boundary layer height h objectively for clear and cloudy conditions and for stable and unstable cases from sounding data is developed. Using this technique, h is thus determined from about 1000 radiosondes taken between 1995 and 2001 during 11 cruises in the eastern Pacific Ocean. An analysis of this data reveals seasonal, interannual, meridional, and zonal variations in h in the cold tongue region, the intertropical convergence zone, and the subtropical stratocumulus region off of the coasts of California and Mexico. Furthermore, it will be shown that this method can also be used in other regions such as the central and western Pacific and over land. Additionally, the marine boundary layer height in the eastern Pacific determined by the Community Climate System Model version 2 (CCSM2) is compared to the objective h determined from radiosondes. Both model results and output from an offline version of the model's parameterization are overall underestimated. It is thus found that a doubling of the model's resolution in approximately the lowest 2 km (from 5 to 10 layers) as well as the adjustment of h within clouds to cloud base or top would significantly improve the determination of h by the model.