Abstract
Abstract. The California Research at the Nexus of Air Quality and Climate Change (CalNex) and Carbonaceous Aerosol and Radiative Effects Study (CARES) field campaigns during May and June 2010 provided a data set appropriate for studying the structure of the atmospheric boundary layer (BL). The NASA Langley Research Center (LaRC) airborne high spectral resolution lidar (HSRL) was deployed to California onboard the NASA LaRC B-200 aircraft to aid in characterizing aerosol properties during these two field campaigns. Measurements of aerosol extinction (532 nm), backscatter (532 and 1064 nm), and depolarization (532 and 1064 nm) profiles during 31 flights, many in coordination with other research aircraft and ground sites, constitute a diverse data set for use in characterizing the spatial and temporal distribution of aerosols, as well as the depth and variability of the daytime mixed layer (ML) height. The paper describes the modified Haar wavelet covariance transform method used to derive the ML heights from HSRL backscatter profiles. HSRL ML heights are validated using ML heights derived from two radiosonde profile sites during CARES. Comparisons between ML heights from HSRL and a Vaisala ceilometer operated during CalNex were used to evaluate the representativeness of a fixed measurement over a larger region. In the Los Angeles basin, comparisons of ML heights derived from HSRL measurements and ML heights derived from the ceilometer result in a very good agreement (mean bias difference of 10 m and correlation coefficient of 0.89) up to 30 km away from the ceilometer site, but are essentially uncorrelated for larger distances, indicating that the spatial variability of the ML height is significant over these distances and not necessarily well captured by limited ground stations. The HSRL ML heights are also used to evaluate the performance in simulating the temporal and spatial variability of ML heights from the Weather Research and Forecasting Chemistry (WRF-Chem) community model. When compared to aerosol ML heights from HSRL, thermodynamic ML heights from WRF-Chem were underpredicted in the CalNex and CARES regions, shown by a bias difference value of −157 m and −29 m, respectively. Better agreement over the Central Valley than in mountainous regions suggests that some variability in the ML height is not well captured at the 4 km grid resolution of the model. A small but significant number of cases have poor agreement when WRF-Chem consistently overestimates the ML height in the late afternoon. Additional comparisons with WRF-Chem aerosol mixed layer heights show no significant improvement over thermodynamic ML heights, confirming that any differences between measurement and model are not due to the methodology of ML height determination.
Highlights
Measurements of atmospheric boundary layer (BL) height are of key importance as a prognostic variable in regional and global weather forecasting and climate models (Atlas and Korb, 1981) and for assessing these models
ML heights derived from high spectral resolution lidar (HSRL) will be extremely useful since it provides spatial and temporal evolution of the mixed layer that cannot be obtained from any other type of information and can more rigorously evaluate meteorological models, such as WRF-Chem
The Carbonaceous Aerosol and Radiative Effects Study (CARES) campaign in the Sacramento region provides the opportunity for verifying the applicability of HSRL derived aerosol ML heights by validating them with thermodynamic ML heights derived from radiosondes
Summary
Measurements of atmospheric boundary layer (BL) height are of key importance as a prognostic variable in regional and global weather forecasting and climate models (Atlas and Korb, 1981) and for assessing these models. The National Research Council (2009) points to inadequacies in current national mesoscale observational capabilities necessary for addressing priorities like forest wildfire smoke dispersion, air quality forecasting, short-range forecasting of high-impact weather, and regional climate modeling. There is interest in BL height research for incorporation into weather and air quality forecasting models and for climate studies. The convective boundary layer (CBL) is characterized by roughly uniform vertical profiles of moisture and potential temperature within that layer (Stull, 1988), and so many researchers use potential temperature to indicate BL height, measured, for example, by radiosonde. The convective boundary layer (CBL) is characterized by roughly uniform vertical profiles of moisture and potential temperature within that layer (Stull, 1988), and so many researchers use potential temperature to indicate BL height, measured, for example, by radiosonde. Atlas and Korb (1981) present the use of aerosol profile measurements made by lidar for determining BL heights, since aerosol gradients can indicate BL heights, where aerosol concentration is sufficient
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
