Impacts of an aerosol layer on a mid-latitude continental system of cumulus clouds: how do these impacts depend on the vertical location of the aerosol layer?

Abstract. Using the large-eddy simulation framework, effects of an aerosol layer on warm cumulus clouds in the Korean Peninsula when the layer is above or around the cloud tops in the upper atmosphere are examined. Also, these effects are compared to effects of an aerosol layer when it is around or below the cloud bases in the low atmosphere. Simulations show that when the aerosol layer is in the low atmosphere, aerosols absorb solar radiation and radiatively heat up air enough to induce greater instability, stronger updrafts and more cloud mass than when the layer is in the upper atmosphere. As aerosol concentrations in the layer decrease, the aerosol radiative heating gets weaker to lead to less instability, weaker updrafts and less cloud mass when the layer is in the low atmosphere. This in turn makes differences in cloud mass, which are between a situation when the layer is in the low atmosphere and that when the layer is in the upper atmosphere, smaller. It is found that the transportation of aerosols by updrafts reduces aerosol concentrations in the aerosol layer, which is in the low atmosphere, and in turn reduces the aerosol radiative heating, updraft intensity and cloud mass. It is also found that the presence of aerosol impacts on radiation suppresses updrafts and reduces clouds. Aerosols affect not only radiation but also aerosol activation. In the absence of aerosol impacts on radiation, aerosol impacts on the droplet nucleation increases cloud mass when the layer is in the low atmosphere as compared to a situation when the layer is in the upper atmosphere. As aerosol impacts on radiation team up with those on the droplet nucleation, differences in cloud mass, which are between a situation when the layer in the low atmosphere and that when the layer is in the upper atmosphere, get larger. This is as compared to a situation when there is no aerosol impacts on radiation and only aerosol impacts on the droplet nucleation.