Characteristics of aerosol vertical profiles in Tsukuba, Japan, and their impacts on the evolution of the atmospheric boundary layer
Authors: Kudo Rei , Aoyagi Toshinori , Nishizawa Tomoaki 
Published: May 2018

Abstract. 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. The
retrieved aerosol vertical profiles of the springtime mean and five transport events were input to our developed
one-dimensional atmospheric model, and the impacts of the aerosol vertical profiles on the evolution of the atmospheric
boundary layer (ABL) were studied by numerical sensitivity experiments. The characteristics of the aerosol vertical
profiles in Tsukuba are as follows: (1) the retrieval results in the spring showed that aerosol optical thickness at
532 nm in the free atmosphere (FA) was 0.13, greater than 0.08 in the ABL owing to the frequent occurrence of
transported aerosols in the FA. In other seasons, optical thickness in the FA was almost the same as that in the
ABL. (2) The aerosol optical and physical properties in the ABL showed a dependency on the extinction coefficient. With an
increase in the extinction coefficient from 0.00 to 0.24 km−1, the Ångström exponent increased from 0.0 to
2.0, the single-scattering albedo increased from 0.87 to 0.99, and the asymmetry factor decreased from 0.75 to
0.50. (3) The large variability in the physical and optical properties of aerosols in the FA were attributed to transport
events, during which the transported aerosols consisted of varying amounts of dust and smoke particles depending on where
they originated (China, Mongolia, or Russia). The results of the numerical sensitivity experiments using the aerosol
vertical profiles of the springtime mean and five transport events in the FA are as follows: (1) numerical sensitivity
experiments based on simulations conducted with and without aerosols showed that aerosols caused the net downward
radiation 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 capping
inversion around the top of the ABL. Consequently, the ABL height was decreased by 133 to 208 m in simulations
with aerosols compared to simulations without aerosols. (2) We also conducted simulations in which all aerosols were
compressed into the ABL but in which the columnar properties were the same and compared with the simulation results for
uncompressed aerosol profiles. The results showed that the reductions in net downward radiation and in sensible and latent
heat fluxes were the same in both types of simulations. However, the capping inversion in the simulations with compression
was weakened owing to aerosol direct heating in the ABL and the lack of direct heating in the FA. This resulted in an
increase in the ABL height, compared with that in the simulations without compression. (3) The dependencies of the
2 m temperature and ABL height on the optical thickness and Ångström exponent in the FA were investigated
using the results of the numerical sensitivity tests. The 2 m temperature and ABL height was decreased with an
increase in the optical thickness, and their reduction rates increase with a decrease in the Ångström exponent because
the optical thickness in the near-infrared wavelength region was large when the Ångström exponent was small.
However, there was a case in which the Ångström exponent was large but the decrease in the ABL height was the largest
of all the simulation results. In this case, the strong capping inversion due to the large extinction coefficient around the
top of the ABL was an import factor. These results suggest that the vertical profiles of the aerosol physical and optical
properties, and the resulting direct heating has important effects on the ABL evolution.