This is a past event.

Please join ATM graduate students, Kadja Flore GALI and Swafuva Varappillikudy Sulaiman for their presentations on Monday,  April 6 at 4 PM - Fisher Hall 101.

Kadja Flore GALI (Advisor: Will Cantrell and Laura Fierce)

THE EFFECT OF AEROSOL PROPERTIES ON CLOUD DROPLET ACTIVATION AND OPTICAL PROPERTIES IN A CONVECTIVE CLOUD CHAMBER.

The response of cloud microphysical properties to aerosol perturbations remains a challenge in predicting the cooling effect of cloud reflectivity. Increasing aerosol number concentrations is known to modify cloud properties; however, the role of underlying aerosol size distributions and compositions in controlling these properties remains unclear. Here, we combine high-resolution large-eddy simulations (LES) with cloud chamber experiments to investigate how aerosol properties (number, size, and composition) and environmental conditions modulate the
cloud microphysics. The results show that cloud droplet activation and deactivation rates depend on both aerosol properties and the environmental supersaturation. However, cloud droplet size distributions and optical properties are primarily controlled by aerosol number concentration across most conditions, with the influence of aerosol size and composition becoming significant only under highly polluted conditions and weak convective forcing. These results suggest that an explicit representation of aerosol size and composition is necessary to accurately resolve the cloud activation and deactivation processes, but under most cloud conditions, cloud reflectivity may be approximated from aerosol number concentration alone. Our findings offer process-level insights into aerosol–cloud interactions and their implications for representation in cloud-resolving and Earth system models.

Swafuva Varappillikudy Sulaiman (Advisor: Will Cantrell)

OPTIMIZING THE EFFICIENCY OF HYGROSCOPIC BURN-IN-PLACE (H- BIP) FLARES THROUGH A SIZE-RESOLVED ANALYSIS

Hygroscopic seeding has evolved into a sophisticated method for precipitation enhancement, with flare-based delivery remaining one of the most widely accepted techniques in the field. Numerous studies have validated the role of hygroscopic flares in inducing precipitation; however, the effectiveness of these flares is closely tied to their microphysical effects after seeding occurs. Here, we investigate the method through a specialized chemical characterization approach, focusing on the size-dependent variations that occur during cloud interaction. The seeding material in flares is typically CaCl2 with KClO4 as an oxidizer to facilitate burning. We conducted Scanning Electron Microscopy analysis of the flare particles immediately post-combustion and — most crucially — of the residual particles extracted from the Michigan Tech Pi Chamber after interaction with a baseline cloud. By isolating residual cloud particles from the cloud chamber, our findings reveal that hygroscopic materials are present in smaller particle sizes. These smaller particles act as additional cloud condensation nuclei, which can diminish flare potency by competing with the larger CaCl2 particles for available water vapor, effectively limiting the growth of individual droplets, which can inhibit the onset of collision-coalescence.