Environmental & Climate Sciences Department Seminar

"Aerosol-cloud interactions in marine warm clouds and implications for Marine Cloud Brightening: On the importance of covarying meteorology and spatiotemporal scales"

Presented by Jianhao Zhang, NOAA CSL/CIRES, China

Thursday, October 12, 2023, 11:00 am — Large Conference Room, Bldg. 490

The devastating socioeconomic impacts of extreme weather events, fueled by climate change, stress the pressing need for effective mitigation strategies. One of the proposed climate intervention (geoengineering) approaches involves enhancing the reflectivity of marine warm clouds through deliberate aerosol injections, known as Marine Cloud Brightening (MCB). The viability of such a geoengineering approach depends crucially on our understanding of aerosol-cloud interactions (ACI) in a changing climate. The long-standing impression that aerosols brighten the clouds stems from the fact that more, smaller cloud droplets are more reflective than fewer, bigger drops, known as the Twomey effect. On the other hand, there is a growing body of literature that suggests cloud water decreases as aerosol loading increases, owing to enhanced evaporation and entrainment. This negative cloud water adjustment partially or even entirely offsets the Twomey brightening effect, depending on environmental conditions. Moreover, scale interactions, both spatially and temporally, involved in these micro- and macro-physical responses make it challenging to constrain the overall cloud brightness responses to aerosol perturbations. In this presentation, I will first introduce a cloud albedo susceptibility assessment framework based on satellite observations. This will be followed by the finding that the potential for cloud darkening, attributed to negative cloud water adjustments, is quite often observed in non-precipitating clouds, especially under deep boundary layers. Next, I will present results from an ensemble of large-eddy simulations that supports the view of a buffered evolution of cloud water adjustments driven by solar heating. Lastly, I will address the detectability cloud brightening in a hypothetical MCB scenario where targeted aerosol injection is implemented, relying on predictions from neural networks trained on climatological fields of meteorology, aerosol, and cloud properties. These findings underscore the benefits of a bespoke MCB strategy compared to perturbing the targeted region uniformly.

Hosted by: Die Wang

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