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

Wednesday, 9 January 2013
Exhibit Hall 3 (Austin Convention Center)
David Painemal, NASA Langley Research Center/SSAI, Hampton, VA; and P. Zuidema

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 ACIτ=dln(τ)/dlnNa, and the relative albedo (A) susceptibility SR-τ=dA/(3dlnτ), with τ and Na denoting cloud optical thickness and aerosol concentration respectively. Both metrics are calculated for fixed intervals of liquid water path (LWP). ACIτ is estimated by combining Na 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. ACIτ values are typically large, close to the physical upper limit (0.33). SR-τ, consistent with satellite estimates, shows values that increase with LWP and τ, reaches a maximum SR-τ (0.089) for LWP (τ) of 58 gm-2 (14), and decreases thereafter. The contribution of ACIτ and SR-τ to the 1AIE is further discussed in this presentation. .55 on 8-10-2012-->
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