The atmospheric boundary layer (ABL) height (h) is a crucial parameter for the treatment of the ABL in weather and climate models. About 1000 soundings from eleven cruises between 1995 and 2001 over the eastern Pacific (including those from the EPIC experiment) have been analyzed to document the large meridional, zonal, seasonal, and interannual variations of h. In particular, its latitudinal distribution in August has three minima: near the equator, in the intertropical convergence zone (ITCZ), and over the subtropical stratus/stratocumulus region near the west coast of California and Mexico. The peak of h in the ITCZ zone (between 5.6N and 11.2N) occurs in the spring (February or April), while it occurs in August between the equator and 5.6N.
Comparison of these data with the 10-year monthly output of the Community Climate System Model (CCSM2) reveals that overall the model underestimates h, particularly from 8.4S to 5.6N in February and north of 20N in August and September. Directly applying the radiosonde data to the CCSM2 formulation for computing h shows that, at the original vertical resolution (with the lowest 5 layers below 2100 m), the CCSM2 formulation would significantly underestimate h. In particular, the correlation coefficient is only 0.06 for cloudy cases. If the model resolution were doubled below 2100 m, however, model results would be significantly improved with a correlation coefficient of 0.78 for cloudy cases.