New Method to Determine Planetary Boundary Layer (PBL) Depth
The depth of the planetary boundary layer (PBL; the lowest part of the atmosphere) is a key factor in many atmospheric processes including cloud formation and aerosol mixing and transport. PBL depth evolves throughout the day due to a number of factors including large-scale air motions, cloudiness, and the daily cycle of solar radiation. Measurements of temperature and moisture from radiosonde profiles are the most reliable method for determining PBL depth, but radiosondes are generally launched only 2-4 times per day. To understand the temporal evolution of atmospheric thermodynamics and evaluate model representations, continuous monitoring of PBL height evolution from remote-sensing measurements is highly desired. U.S. Department of Energy investigators have developed a new method to determine PBL depth that combines the strengths of two existing gradient methods and that can be applied to data from radiosondes, micro-pulse lidar (MPL), and atmospheric emitted radiance interferometer (AERI). The method was applied to measurements from all three instruments acquired at the Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site during the period 1996-2004 to produce a time series of PBL depth. The seasonal and diurnal cycles were compared among the three instruments, revealing that the results are more reliable in winter than in summer. There is better agreement between instruments during daylight hours than at night, and also at times of day when the PBL is mature rather than collapsing or developing. While the PBL depth cannot be detected from AERI data if clouds are present, or from MPL data if the boundary layer is shallower than 600 m, both instruments have much higher temporal resolution than radiosondes. The more detailed view of PBL variation over time from the AERI and MPL can capture details of the diurnal cycle, which will be useful for evaluating PBL simulation in climate models.
Sawyer, V., and Z. Li. 2013. “Detection, Variations and Intercomparison of the Planetary Boundary Layer Depth from Radiosonde, Lidar, and Infrared Spectrometer,” Atmospheric Environment 79, 518-28.