First aerosol indirect effect estimates in marine stratocumulus clouds using airborne observations during VOCALS-REx

The first aerosol indirect effect (1AIE) is investigated over the Southeast Pacific during the VAMOS Ocean-Cloud-Atmosphere-Land Study Regional Experiment (VOCALS-REX) through a combination of in situ and remotely-sensed aircraft (NCAR C-130) observations. The albedo of this region has previously been identified as highly susceptible to aerosol. The 1AIE is broken down into the product of two independently-estimated terms: The cloud aerosol interaction metric ACI_τ=dln(τ)/dlnN_a, and the relative albedo (A) susceptibility S_R-τ=dA/(3dlnτ), with τ and N_a denoting cloud optical thickness and aerosol concentration respectively. Both metrics are calculated for fixed intervals of liquid water path (LWP). ACI_τ is estimated by combining N_a sampled within the boundary layer, with τ and LWP derived from upward-looking broadband and millimeter-wave radiometers, respectively. The 1 Hz sub-cloud observations are collected during four eight-hour daytime flights by the C-130 aircraft. ACI_τ values are typically large, close to the physical upper limit (0.33). S_R-τ, consistent with satellite estimates, shows values that increase with LWP and τ, reaches a maximum S_R-τ (0.089) for LWP (τ) of 58 gm^-2 (14), and decreases thereafter. The contribution of ACI_τ and S_R-τ to the 1AIE is further discussed in this presentation. .55 on 8-10-2012-->