Improving convective transport, wet removal, and vertical distribution of aerosols in CAM5
Authors
Hailong Wang — Pacific Northwest National Laboratory
Dick C Easter — Pacific Northwest National Laboratory
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Qing Yang — Pacific Northwest National Laboratory
Balwinder Singh — Pacific Northwest National Laboratory
Jerome D Fast — Pacific Northwest National Laboratory
Phil Rasch — National Center for Atmospheric Research (NCAR)
Category
Modeling
Description
It is important to simulate the correct vertical distribution of aerosols in climate models. Some aerosol species in the mid- troposphere and upper troposphere may affect ice cloud formation, and the vertical distribution of light-absorbing aerosols like black carbon (BC) influences local radiative heating and, consequently, the thermodynamic structure and circulation. Aerosol lifetime increases with altitudes because dry and wet deposition processes operate more strongly at the surface, affecting aerosol transport and removal.The vertical distribution of aerosols in the free troposphere depends strongly on vertical transport and wet removal by convective clouds. Many global aerosol and climate models, including the widely used Community Atmosphere Model version 5 (CAM5), have large biases in predicting aerosols in the upper troposphere. In the standard CAM5, convective transport and wet removal of aerosols are treated separately, and secondary activation of aerosols entrained into updrafts is ignored. We recently introduced into CAM5 a new unified scheme for convective transport and wet removal of aerosols, with explicit aerosol activation above convective cloud base. This new implementation reduces the excessive aerosol aloft and better simulates observed BC profiles, which show decreasing mixing ratios in the mid-troposphere to upper troposphere, especially in the tropics and midlatitudes. The improved aerosol distributions have other impacts on CAM5, improving the global mean liquid water path and cloud forcing.
We will use the Weather Research and Forecasting (WRF) modeling framework with CAM5 physics to study transport and scavenging of aerosols by deep convective clouds, with fine-resolution cloud-resolving simulations and coarser-resolution simulations employing convective cloud parameterizations. Measurements from recent field campaigns will be utilized for process-level evaluation of model simulations.