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. Vertical profiles of the aerosol physical and optical properties, with a focus on seasonal means and on transport events,were investigated in Tsukuba, Japan, by a synergistic remote sensing method that uses lidar and sky radiometer data. Theretrieved aerosol vertical profiles of the springtime mean and five transport events were input to our developedone-dimensional atmospheric model, and the impacts of the aerosol vertical profiles on the evolution of the atmosphericboundary layer (ABL) were studied by numerical sensitivity experiments. The characteristics of the aerosol verticalprofiles in Tsukuba are as follows: (1) the retrieval results in the spring showed that aerosol optical thickness at532  nm in the free atmosphere (FA) was 0.13, greater than 0.08 in the ABL owing to the frequent occurrence oftransported aerosols in the FA. In other seasons, optical thickness in the FA was almost the same as that in theABL. (2) The aerosol optical and physical properties in the ABL showed a dependency on the extinction coefficient. With anincrease in the extinction coefficient from 0.00 to 0.24  km−1 , the Angstrom exponent increased from 0.0 to2.0, the single-scattering albedo increased from 0.87 to 0.99, and the asymmetry factor decreased from 0.75 to0.50. (3) The large variability in the physical and optical properties of aerosols in the FA were attributed to transportevents, during which the transported aerosols consisted of varying amounts of dust and smoke particles depending on wherethey originated (China, Mongolia, or Russia). The results of the numerical sensitivity experiments using the aerosolvertical profiles of the springtime mean and five transport events in the FA are as follows: (1) numerical sensitivityexperiments based on simulations conducted with and without aerosols showed that aerosols caused the net downwardradiation and the sensible and latent heat fluxes at the surface to decrease. The decrease in temperature in the ABL( − 0.2 to − 0.6  K ) and the direct heating of aerosols in the FA (0.0 to 0.4  K ) strengthened the cappinginversion around the top of the ABL. Consequently, the ABL height was decreased by 133 to 208  m in simulationswith aerosols compared to simulations without aerosols. (2) We also conducted simulations in which all aerosols werecompressed into the ABL but in which the columnar properties were the same and compared with the simulation results foruncompressed aerosol profiles. The results showed that the reductions in net downward radiation and in sensible and latentheat fluxes were the same in both types of simulations. However, the capping inversion in the simulations with compressionwas weakened owing to aerosol direct heating in the ABL and the lack of direct heating in the FA. This resulted in anincrease in the ABL height, compared with that in the simulations without compression. (3) The dependencies of the2  m temperature and ABL height on the optical thickness and Angstrom exponent in the FA were investigatedusing the results of the numerical sensitivity tests. The 2  m temperature and ABL height was decreased with anincrease in the optical thickness, and their reduction rates increase with a decrease in the Angstrom exponent becausethe optical thickness in the near-infrared wavelength region was large when the Angstrom exponent was small.However, there was a case in which the Angstrom exponent was large but the decrease in the ABL height was the largestof all the simulation results. In this case, the strong capping inversion due to the large extinction coefficient around thetop of the ABL was an import factor. These results suggest that the vertical profiles of the aerosol physical and opticalproperties, and the resulting direct heating has important effects on the ABL evolution.

Characteristics of aerosol vertical profiles in Tsukuba, Japan, and their impacts on the evolution of the atmospheric boundary layer