How Sensitive are Deep Convective Clouds to Aerosol Perturbations?

Speaker: Zachary Lebo, NCAR/ASP

When: Wednesday, May 15, 2013, 3:30 p.m. Mountain Time
Location: Room 2A305, DSRC (NOAA Building), 325 Broadway, Boulder
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Much attention has been given in recent years to the "invigoration" of deep convection due to increased aerosol number concentration. Fundamentally, aerosol number concentration and cloud droplet number concentration are directly linked but post cloud droplet activation, a multitude of complex microphysical processes presents a particularly challenging problem to address, especially in deep convective clouds. A physical basis for the interactions between the aerosol-induced changes in cloud microphysical process rates is prudent to understanding how these systems may be intensified in regard to strength and precipitation. Particular attention will be given to simulations of squall lines over a wide range of both aerosol number concentration and low-level environmental shear. The dynamical effects of aerosol perturbations on these systems will be discussed in the context of RKW theory to both demonstrate and quantify these effects. RKW theory describes how the strength and structure of squall lines is directly tied to the balance between cold pool-induced and wind shear-induced circulations. Moreover, the applicability of the results to other forms of deep convection will be presented. Lastly, previous works have speculated that the "invigoration" of deep convection is a direct result of low-level aerosols acting to mitigate warm-rain processes and thus loft more droplets into the mixed-phase region of the cloud. Sensitivity simulations demonstrate that an increase in low-level aerosol number concentration alone has little effect on the storm dynamics, especially in comparison to increased aerosol loading in the free troposphere.