Comparison of Mixing Heights using Radiosondes and the Vaisala CL31 Mixing Height Algorithm

A main focus of the 2009 SHARP (Study of Houston Atmospheric Radical Precursors) campaign is to investigate the conditions favorable for springtime ozone formation in the Houston-Galveston area (HGA). A continuously measuring Vaisala Celiometer CL31 was installed at the University of Houston Main Campus because of its ability to monitor the diurnal evolution of the planetary boundary layer (PBL), which plays an important role in ozone formation. The beta version of the CL31 mixing height algorithm is utilized in this study because it is capable of describing the overall boundary layer structure in great detail. This feature selects the maximum negative gradient of the backscatter as the top of the mixed layer (which corresponds to the concentration of particulate matter) and assumes that the particulate matter concentrations are relatively constant in the PBL and then fall off at the top of the PBL. The algorithm also has the ability to identify multiple maximum negative gradients simultaneously, which in addition to the mixing height, may also include the residual layer, aerosol layer, and low level jet among others. To assess the overall effectiveness of the algorithm, mixing heights derived from radiosonde profiles are compared to CL31 derived mixing heights. Three Intensive Observing Periods (IOPs) corresponding to high ozone periods during the SHARP campaign are used for the comparison.