High-resolution properties of the equatorial Pacific marine atmospheric boundary layer from lidar and radiosonde observations

A ''thermostat'' mechanism for cooling the Equatorial Pacific is being tested with data collected during the Central Equatorial Pacific Experiment. The Los Alamos National Laboratory participated by fielding two shipboard lidars that collected nearly continuous data over the Pacific from 10 to 21 March 1993 as the ship sailed from Guadalcanal to Christmas Island. A Raman lidar measured water vapor mixing ratio in the lower troposphere, especially in the marine atmospheric boundary layer (ABL), and an aerosol backscatter lidar measured height and thickness of clouds to an altitude of 20 km. The data collected from these two lidars were used to determine ocean-atmosphere phenomenology, which in turn, affects the climatology of the Central Pacific. Agreement between coincident radiosonde and the Raman water vapor lidar measurements was typically within +/-0.25 g kg(-1) of water. Divergence between the two instruments occurred at transitions between distinct layers in the lower marine atmosphere. Reasons for this divergence will be discussed. Above the ABL the lidar and radiosonde are in excellent agreement. A wealth of detail is apparent in the lidar-derived profiles. For example, there are large variations in water vapor mixing ratio-the expression of the inherent low-frequency, intermittent, atmospheric turbulence that produces spatially discrete features such as convective plumes. These features define the structure and extent of the ABL. Using the ABL structural characteristics, an analysis of the relationship between entrainment zone (EZ) height and observed sea surface temperature (SST) revealed counterintuitive behavior-that the height of the EZ decreases as SST increases in the range between 27 degrees and 30 degrees C.