A065-0007
Impacts of Aerosol Vertical Distribution and Single Scattering Albedo on Planetary Boundary Layer Structure: WRF SCM simulations

Wednesday, 9 December 2020
Poster
Xiaoyan Zhang1,2, Changjie Cai2, Xiao-Ming Hu3,4, Lan Gao5 and Jun Hu6,7, (1)Nanjing University of Information Science and Technology, School of Atmospheric Science, Nanjing, China, (2)University of Oklahoma Health Sciences Center, University of Oklahoma, Occupational and Environmental Health, Oklahoma City, United States, (3)University of Oklahoma Norman Campus, Center for Analysis and Prediction of Storms, Norman, OK, United States, (4)University of Oklahoma Norman Campus, School of Meteorology, Norman, OK, United States, (5)University of Oklahoma Norman Campus, School of Meteorology, Norman, United States, (6)University of Oklahoma Norman Campus, Center for Analysis and Prediction of Storms, Norman, United States, (7)Nanjing University of Information Science and Technology, School of Atmospheric Physics, Nanjing, China
Abstract:
Aerosol vertical distribution, scattering and absorption play critical roles in affecting atmospheric radiative budget, thereby influence the planetary boundary layer (PBL) structure. In this study, we investigated the impacts of aerosol layer heights with various aerosol single-scattering albedo (SSA) values on the meteorological variables, then the PBL development during daytime. We designed three aerosol-layer height scenarios using a Gaussian vertical distribution in the WRF Single Column Model (SCM) simulations, with the peak aerosol concentration (1) near the surface, (2) right below the PBL height, and (3) right above the PBL height. For each scenario, we analyzed the impacts of aerosols with three observable SSA values (0.85, 0.90 and 0.95) on the meteorological variables, and then the PBL structure. The results showed that, in all scenarios, aerosols reduced the surface heat flux and induced negative net heating rate profiles that inhibited the PBL development. Aerosols concentrated right below the PBL height had the strongest inhibition effect on PBL development due to a thickest entrainment zone, resulting in the lowest PBL height, especially in the most absorbing aerosol case (SSA = 0.85). When these aerosols concentrated near the surface, although the neutral point of potential temperature profile increased suggesting more unstable lower atmosphere, PBL height is still suppressed. Strong absorptive aerosols concentrated near the surface could enhance vertical mixing by absorbing heat resulting in the PBL height increase (stove effect) according to previous modeling studies. Similar stove effect was observed by setting SSA values less than 0.6 in this study; however, such small SSA values have never been observed from any observational and satellite retrieval data worldwide. Our study also found that aerosols delayed the PBL development in the morning, and promoted its collapse in the afternoon, which are consistent with previous studies.

In sum, the results from this study proposed that (1) the aerosols inhibit the PBL development under all conditions (aerosol layer at different heights with various reasonable SSA values) regardless of a more stable or unstable lower atmosphere, and (2) enriched our knowledge of the relationship between lower atmospheric stability and PBL height.

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